Chainsaw Repair

Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Dolmar Makita => Topic started by: Mastermind on December 30, 2011, 01:11:36 am


Title: Dolmar 7900 Porting Info
Post by: Mastermind on December 30, 2011, 01:11:36 am
Hello guys. I see a lot of knowledgeable folks hanging out here. Thought I might try to get a discussion going on building the 7900. I've never done one, and am intrigued with this saw because of the many things I've heard about them.

1. The skirts are not very wide.

2. Many different piston can be used with a spacer.

3. They "like" a bunch of blowdown. 

I do plan to build one soon and would like to glean some knowledge from folks that have some experience with this model.
Title: Re: Dolmar 7900 Porting Info
Post by: rms61moparman on January 02, 2012, 07:16:47 pm
Have you tried finger ports yet Randy??
One of the most impressive 7900s I've seen is finger ported and is is a butt kicker and name taker!


Mike
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 02, 2012, 07:24:41 pm
I've not tried finger ports YET. I do need to do that though.
Title: Re: Dolmar 7900 Porting Info
Post by: rgclmc on January 02, 2012, 07:32:21 pm
What does blowdown refer to?
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on January 02, 2012, 07:45:47 pm
The one I had had finger ports put in it by Dave Neiger.  That saw was the best running 7900 I ran back in 07-09 till these new ones are coming out like ginks.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 02, 2012, 11:34:07 pm
What does blowdown refer to?

It's the time from the exhaust port opens until the transfer ports open.

I remember when Frank's saw was built. I would like to run that puppy. :)
Title: Re: Dolmar 7900 Porting Info
Post by: rms61moparman on January 05, 2012, 06:35:33 pm
Well Randy,

I've got a couple of..."candidates" around here if you start thinking you want to practice.
How about a BB 7900?


Mike
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 05, 2012, 06:55:28 pm
I have one on the way and two others in the wings. I just wonder if finger ports are the way to go on these saws?  ;D

For you though Mike........anything my friend.
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 05, 2012, 09:30:01 pm
see that is where you get into trouble , are these real worksaws or run a couple tanks a year cutting wood or cookies and are called worksaws , If the saw is going to be run 8 plus hours a day 5 or 6 days a week and is to last 2000 hours plus  then finger ports are not the way to go , One thing I have built and that is alot of 7900's , I even built 4- 7300/7900 for Dolmar themselves with 3 of those going to Africa , 7900 to me is a great saw and I like them alot , the only thing I change is the ring , I like the husky ring better and I feel it stands up better . Now on the saws for dolmar I had to use their piston and their coil setup so that limits you alot right there cause the 7900 sure is a narrow skirted piston so ports are narrow as well . These saws they are putting different pistons in that makes you build a spacer plate and lots of other stuff is not what I call a worksaw , Reason for so much blow down is the crankcase volume is very tight on them , if you raise the transfers up like on a ported 372 it will lay down in the cut once you put it under load , I'm talking like cutting 20 plus inch stuff
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 05, 2012, 09:36:38 pm
That's the stuff I'm looking for on this. I've built more than a few saws, but the 7900 is new to me.

The saw I'm thinking about will be more of a GTG saw than an everyday worksaw, so.....
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 05, 2012, 11:22:52 pm
then put a wider skirted piston in it , remember some saws have a real wide skirt piston in them at these GTG's so pretty much a real racesaw , if you use the stock piston get the compression up as high as you can as that helps the 7900 alot and the higher compression works very good with the tight crankcase volume , if you raise your transfer ports to high it will boil the gas in the crankcase real bad and have less power so watch how high you raise them
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 05, 2012, 11:30:59 pm
I really appreciate you input on this. It's plain to see that you are no stranger to the 7900.

What piston would you recommend? And could you share a little about using a Husky coil?
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 05, 2012, 11:52:28 pm
I have done alot of 7900's , 99% were worksaws but have built a couple race 7900's on alcohol , on muffler or pipe , Myself I would use the 272 piston as its a single ring , I have made my own 7900 wide skirt pistons but that takes me alot of time , now you will have to build a spacer plate which I know is nothing for you cause the 272 piston is taller than the 7900 piston but also with using the 272 piston you donot need to grind your crankcase as much as with a 7900 wide skirt  piston cause the skirts hit the crankcase at BDC,

No secret on the coil , its a 272 coil and retime the flywheel, , the easiest way for me to tell you how to time the coil to the flywheel is find someone that will let you time a stock 272 , Get a dial gauge in your sparkplug hole , find TDC and look at where the coil matches the flywheel magnets , transfer the coil over and start your motor at TDC and mount the flywheel to the same spot of the magnet or you can go advance the flywheel a touch over the stock 272 setup, I know most transfer the coil onto the 7900 metal part but I just use the 272 coil setup and make the holes line up
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 06, 2012, 11:25:34 pm
Ed I sure to enjoy you giving me the chance to learn these things from you. I'll be talking with the saw's user about how far he wants to take this build. I'll post it all here if that's ok, I'll need some help with this one.
Title: Re: Dolmar 7900 Porting Info
Post by: StumpysCustoms on January 07, 2012, 12:01:24 am
My second post & already lovein this site.  Thanks Ed for letting out some of the secrets of the 7900. ;)
I think I may be gitting a 6400 in on trade in the near future that I'll do some playin with. 
I've learned alot in just a few minutes from this thread.  Thanks fellers :-*


fixed it for you  ;)
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on January 07, 2012, 06:32:30 am
My second post & already lovein this site.  Thanks Eric for letting out some of the secrets of the 7900. ;)
I think I may be gitting a 6400 in on trade in the near future that I'll do some playin with. 
I've learned alot in just a few minutes from this thread.  Thanks fellers :-*

EHP is Ed Heard.  Not eric.  ;) 
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 07, 2012, 09:06:04 am
That's a first  ;D
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 07, 2012, 09:56:54 am
What you said about the tight crankcase of the 7900 got me to thinking.......

When we build these hybrids.....044/046 comes to mind. I just wonder if more blowdown would be better on these as well?

The funny thing about these two strokes is the more I learn, the less I know.  ???
Title: Re: Dolmar 7900 Porting Info
Post by: man of stihl on January 07, 2012, 10:17:04 am
I just bought a 7900 basket case, so I'll be watching this thread closely. :) Ed. When you say get the compression up as high as you can. Were talkin what? 175+?
Title: Re: Dolmar 7900 Porting Info
Post by: rms61moparman on January 07, 2012, 10:42:39 am
More like 175+++

Mike
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 07, 2012, 11:02:42 am
compression goes back to the same problem, how much port timing did you put in the motor , less port timing the more compression you can run unless you run race gas of some kind , same thing with your flywheel timing the more advance you run the flywheel the less compression you can run cause its going to get real hot fast . I donot like running any saw on pump gas above 175 psi on my gauge cause first in most cases it will blow up second it will not be as fast or last as long as a saw running 160 to 170 psi that has had the other stuff do to it , Most high test pump gas is 91 or so octane now and at least 10% ethanol so you have to consider what your have for fuel cause its no good building a saw that has to run on C12 or something like that if the saw is to be a worksaw not a weekend cookie cutter , another thing  the higher the compression in most cases the shorter the main bearing last , I got 7900's that are out there with tree companys that are 7 years old and work pretty much every day , I did see 2 this summer come back for main bearings from 7 years of work so that is pretty good in my mind
Title: Re: Dolmar 7900 Porting Info
Post by: Old Iron Logging on January 07, 2012, 11:19:00 am
Ed, what if the saw stock is running in the 190 lbs plus range to start with? We see more than a few saws at the shop in the 190-210 range stock.
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 07, 2012, 12:56:31 pm
I guess like I said it depends on the gauge , I have not see much of the newest strato stuff as most guys here are staying away from that , if you got 190 psi on my gauge and is running on pump gas then it has low porting and in most cases a large blow down time . I had 2-288's come in here last summer that were stock but they pulled the base gasket  and in real nice shape but were in the 180 psi, in 16 inch maple they were fine but in the bigger 40 inch plus stuff they would lay down in the cut bad, good thing the guys running them knew to stop and see what was wrong , I just lowered the compression to 170 psi and they said they worked great , Now mostly I blame this on our great gas we are getting now and if you have better gas then you most likely will not see these problems but believe me the more ethanol you get the worse this problem is going to get and another big problem coming is alot of 2 stroke oils will not mix with ethanol and the ones that do cost lots of money and hard to get in some areas . I know when guys from NY come up and play with their saws they have to richen them up to run our high test pump gas which tells me ours has more ethanol in it
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 07, 2012, 01:21:15 pm
another thing I have noticed and this is with saws like the 361 , if they were sold in this area they all are low compression with the thicker base gasket , if they came from up north where I'm from they were the higher compression with the thinner base gasket .

The higher the compression the more carefull the operator has to be on making sure he keeps the engine heat down .

Now back to dolmar , if you put a unlimited coil in it make sure to use lots of oil like 32-1 cause it going to turn alot of revs , 16,000 rpms  happens all the time with say a 20 inch bar , I have seen over 17,000 rpms on a woodported saw on a pipe and that was where it cut best at , One thing I have not seen yet on the 7900 is a crank go bad , I was playing with a 7900 on alcohol on muffler and was doing my cuts the the return spring on the 3120 carb broke so now the throttle is wide open , I got the top covers on the saw so no way to get at the carb, the off switch is not going to work in that state with the carb wide open cause the blade never came down after the run and now the plug  is glowing so in a split second I figured I wanted nothing to do with this problem so I threw the saw cause I figured the rod would be coming out to meet me  ;D, it ran about 5 seconds on the ground before the flywheel came loose and she finally quit , I checked the crank and I see nothing wrong , it did not spin on the crank pin so not as bad as I thought , I'm sure 20,000 rpms were passed cause it sure was screaming
Title: Re: Dolmar 7900 Porting Info
Post by: StumpysCustoms on January 07, 2012, 01:43:30 pm
Sorry Ed,  I feel dumb,  what else is new. 
Thanks anyways for all the info.  I'm with Randy on this,  the more I learn the dumber I feel.
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 07, 2012, 02:52:19 pm
Believe this , if any one tells you that they know everything , tell them they are full of BS as new ways to skin the cat get figured out every day and if no one ever thought outside the box nothing would change  ;D, and donot worry Stump , I'm not the smartest tool in the shed  :o but I always think outside the box cause its more fun out there
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 07, 2012, 08:48:03 pm
Another thing I should put in here put I'm sure somewhere else I have said this , the small the cc's of the saw the higher you can run your BEMP, what psi you run in a 50-60cc saw and it can live you will not run in a 120cc saw with the same porting numbers and crankcase ratio , Just something to think about , if you take the crankcase ratio of a 3120 , which is in the 1.4's and make it 1.20  the amount of horsepower you will gain is unbelievable as 1.20 is the idea ratio but the same thing , your amount of fuel needed is almost double so just like everything else , how much power do you need and what is that power going to cost you  in fuel, shorten the life of the saw if you go to wild , make the saw not very user friendly as its a prick to keep running
Title: Re: Dolmar 7900 Porting Info
Post by: Andyshine77 on January 08, 2012, 12:09:43 am
Sorry Ed,  I feel dumb,  what else is new. 
Thanks anyways for all the info.  I'm with Randy on this,  the more I learn the dumber I feel.

Stump you speak the truth mang!!!!!
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 08, 2012, 10:24:30 am
The quote thingy ain't working for me...... :-[

Ed the ratio your speaking of, is this crankcase to displacement?
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on January 08, 2012, 10:31:25 am
The quote thingy ain't working for me...... :-[

Ed the ratio your speaking of, is this crankcase to displacement?

Read the 2 ways to do it since update by server.   http://chainsawrepair.createaforum.com/general-discussion/%27quote%27-not-working/
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 08, 2012, 10:38:32 am
The quote thingy ain't working for me...... :-[

Ed the ratio your speaking of, is this crankcase to displacement?

Read the 2 ways to do it since update by server.   http://chainsawrepair.createaforum.com/general-discussion/%27quote%27-not-working/

Cool. :)
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 08, 2012, 10:26:54 pm
Sorry I thought someone answered your question and yes its total volume to engine cc ratio
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 10, 2012, 07:36:44 pm
I will be building a 7900 worksaw here again in a week or so, it will have the unlimited coil in it thou , not sure why but the owner wants one in it , the saw will be used to block firewood mostly in the 20 to 24 inch diameter in oak and maple
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 10, 2012, 11:28:46 pm
I will be building a 7900 worksaw here again in a week or so, it will have the unlimited coil in it thou , not sure why but the owner wants one in it , the saw will be used to block firewood mostly in the 20 to 24 inch diameter in oak and maple

I have one here to build as well. I need a few days to get caught up before I start on it. The owner says he wants a GTG saw out of it so...........

What would you recommend????

Thanks Ed for the replies.
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 11, 2012, 07:18:02 am
if your using the stock piston then becarefull on the port timing , really watch your transfer porting as to high the motor lays down in the cut but if the guy can run the saw and cutting smaller wood then you can get away with the higher transfers , so go after compression
Title: Re: Dolmar 7900 Porting Info
Post by: w8ye on January 11, 2012, 09:45:03 am
But is the combustion chamber pent roof offset in the 7900?

If so, it would require some fancy offset machining for the pop up?
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 11, 2012, 10:30:04 am
But is the combustion chamber pent roof offset in the 7900?


If so, it would require some fancy offset machining for the pop up?


The offset popup is not an problem. They are no harder to make than a standard popup.

When you add a D shape to an offset the milling machine comes into play, but it still is just a simple task.

if your using the stock piston then becarefull on the port timing , really watch your transfer porting as to high the motor lays down in the cut but if the guy can run the saw and cutting smaller wood then you can get away with the higher transfers , so go after compression

I'll be tearing it down in the next few days to clean it up real well. If the piston has any wear to speak of I'll try to get a 272 piston.

I just did a 064BB with a 395 piston and it has a butt load of torque but not as much unloaded rpm as I used to seeing on an 1122 series Stihl.

I'll be going back in it another time or two.  ;)
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 11, 2012, 03:20:18 pm
just watch how many rpms you end up turning with those 395 pistons cause they break , the ring land cannot stand real high rpms at all and yes that is on OEM
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 11, 2012, 04:43:03 pm
The BB Stihl is turning 13,400
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 11, 2012, 07:14:49 pm
that should be safe , I never had much trouble on gas but lots of trouble on alcohol , On muffler none broke but as soon as you put them on pipe and try turning 13,800 rpms in the wood they seem not to be able to stand that
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun on January 15, 2012, 02:23:05 pm
Sometimes I think people are pushing the envelope just a little to far to be calling saws a woods ported work saw.  Here is a 7900 crank after a porter in northern Ohio had a oops with a customers saw.  :o Yep I seen this first hand.
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 15, 2012, 07:12:49 pm
piston broke or a ring snagged ?
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 15, 2012, 07:15:49 pm
I like the answer you get sometimes when they are talking about these GTG's there having now and out right tell you that the saw they have is a work saw so it will not be even close to the others , Last time I thought a woodsport meant it was to be able to go cut 8 hours straight everyday without any trouble not 3 cookies and call it a day
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on January 15, 2012, 07:17:45 pm
Memory is pretty bad on exact reason, but thinking it was due to snagging.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on January 15, 2012, 08:48:53 pm
I like the answer you get sometimes when they are talking about these GTG's there having now and out right tell you that the saw they have is a work saw so it will not be even close to the others , Last time I thought a woodsport meant it was to be able to go cut 8 hours straight everyday without any trouble not 3 cookies and call it a day

I couldn't agree more. The saws I build are for real use. I wouldn't cut a port to 70% or even more and think that saw would hold up to a hard weeks work. Or build a saw with over 200psi and think that saw is a real work saw.

I'll start on two 7900's tomorrow.....real work saws though. I asked the owners what their plans were for these saws and if they had any interest in going with a different piston or anything. Firewood and GTGs is the plan for them both so durability is what I'm shooting for.

Now I will be building a 7901 for myself that might be a bit different. :)
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on January 15, 2012, 10:28:18 pm
Either way that 7900 I'm sure the piston broke as I have seen rods that look like that before  ;D just not on a 7900 , If a guy is really going to use a saw to block firewood with it has to be built to handle all the heat a motor is going to make , Not sure if any one else does this but on a new saw I will cut cookies hard with it then place my hand above the bar cover side plate and feel how hot the heat is coming of the jug , the flywheel will blow the heat out on your hand , if the heat is real hot then she is to hot for a worksaw in most cases
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on May 06, 2012, 08:14:15 pm
just working on a 7900 with heated handles , man lots of wires  that is for sure , never seen a heated 7900 before , its pretty much new but had a fight with a tree and the tree won  ;D, it will be ported before the night is over
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on June 29, 2014, 01:41:15 pm
Good read.
Title: Re: Dolmar 7900 Porting Info
Post by: pete on June 29, 2014, 11:49:55 pm
I enjoyed it as well  :) another couple of hundred threads like it and I might be able to actually understand it all. But bit by bit it is making sense
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on June 29, 2014, 11:59:37 pm
A crapp load of saws have passed in front of me since this thread started.

Here something I tried not long ago.

Too wide on the uppers really......but a fun saw to run.

(http://i1160.photobucket.com/albums/q498/Mastermind7864/MMWS%20FP7900XP/7900FP001_zpsc50d0645.jpg) (http://s1160.photobucket.com/user/Mastermind7864/media/MMWS%20FP7900XP/7900FP001_zpsc50d0645.jpg.html)
Title: Re: Dolmar 7900 Porting Info
Post by: mdavlee . on June 30, 2014, 12:18:23 am
I bet that one would run a shorter bar good.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on June 30, 2014, 12:28:20 am
Sir yes sir.

395xp carb.
Title: Re: Dolmar 7900 Porting Info
Post by: mdavlee . on June 30, 2014, 02:22:13 am
How much work was the 395 carb?
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on June 30, 2014, 08:44:02 am
Not a problem. Use a 372 intake boot, cut the ear off and twist is some, so the carb sits level again. There was something with the cable too. I can't remember.

On the air filter elbow.....use one from a 395 or a 272....etc. 
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun on June 30, 2014, 09:43:27 am
A **** load of saws have passed in front of me since this thread started.

Here something I tried not long ago.

Too wide on the uppers really......but a fun saw to run.

(http://i1160.photobucket.com/albums/q498/Mastermind7864/MMWS%20FP7900XP/7900FP001_zpsc50d0645.jpg) (http://s1160.photobucket.com/user/Mastermind7864/media/MMWS%20FP7900XP/7900FP001_zpsc50d0645.jpg.html)

Nice. So how did it do?

Randy could you remind me for the 100thteen time what the stuff is you use for base sealer again?    I can never remember.   Maybe if in type here I will have something fall back on. Thanks.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on June 30, 2014, 09:52:45 am
I use Loctite 518.

The parts have to be dead clean......and it needs to cure for 12 hours.
Title: Re: Dolmar 7900 Porting Info
Post by: Nathaniel Vansickle on June 30, 2014, 10:04:35 am
I use Loctite 518.

The parts have to be dead clean......and it needs to cure for 12 hours.

Have you or anyone else tried 515?  similar stuff a bit easier to spread out. That is what echo recommends on some of their crankcases along with threebond.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on June 30, 2014, 11:25:15 am
Anyone know if there is ANY actual differences between the OEM Dolmar 7900 cylinder and the OEM Solo 681 cylinder?
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on June 30, 2014, 11:29:58 am
Never checked but there has to be port timing difference IMO.  The stock 681's I ran were so strong and it cant be because of just 1mm more stroke. Just my guess.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on June 30, 2014, 11:36:25 am
Never checked but there has to be port timing difference IMO.  The stock 681's I ran were so strong and it cant be because of just 1mm more stroke. Just my guess.

I agree add what you said to the fact that you need a 1.5mm spacer to make the NWP BBK Dolmar jug work on the 681. There must be some sort of timing difference!
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on June 30, 2014, 11:39:55 am
Redprospector had this to say long ago. Romeo & I did a side by side comparison between a stock (broke in) 7900, and the brand new stock 681 (actually it's very first cuts), same bar & chain in (if I remember right) a 21" log. The Solo out cut the Dolmar by almost a second a cut pretty consistently. That's not that big a deal when you're out in the woods bucking logs, but it is braggin' rights.

Both were loggers and racers and no how to run and time saws correctly.  ;)

Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on June 30, 2014, 12:01:01 pm
Going to find out if I can get a 681 C/P kit from Solo. Wish me luck!
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on June 30, 2014, 12:04:14 pm
Brad had the stock 681 numbers.  no stock OEM 7900 timing numbers found yet.

681 OEM
Exhaust 105
Transfers 131
Intake 81




Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on June 30, 2014, 12:11:31 pm
Never checked but there has to be port timing difference IMO.  The stock 681's I ran were so strong and it cant be because of just 1mm more stroke. Just my guess.

I agree add what you said to the fact that you need a 1.5mm spacer to make the NWP BBK Dolmar jug work on the 681. There must be some sort of timing difference!

1mm difference in stroke will cause quite a difference in port timing.  Putting a larger stroke in a saw without changing port heights will cause longer exhaust and transfer duration, shorter intake duration.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on June 30, 2014, 01:27:23 pm
I use Loctite 518.

The parts have to be dead clean......and it needs to cure for 12 hours.

Have you or anyone else tried 515?  similar stuff a bit easier to spread out. That is what echo recommends on some of their crankcases along with threebond.

Yeah Nate......I tried 515 too. I had some base leaks with it. That's why I only use 518 now.
Title: Re: Dolmar 7900 Porting Info
Post by: farmboy on June 30, 2014, 08:07:18 pm
Stump's timing #'s stock 7900 http://www.arboristsite.com/community/threads/project-stumpbroke-makita-7900.197324/
Ex. 150*
Tr. 96*
In. 156*
BD 27*
Sq. .021
Tim,
I knew Baileys used to carry the 1.5mm spacer separate I found my link I had saved PN: 68115 NLA separate now.
Shep
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on June 30, 2014, 09:11:06 pm
We compared the 681 vs 7900 port timing numbers when we had the 681 build off that Romeo (Sean) participated in.  He and Redprospector and myself checked timing we came to the conclusion the jugs were the same.  It is my understanding that Solo designed the 7900 for Dolmar. Wasn't there a few other models that were rebadged Solo saws in the Dolmar line up?? Adam
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on June 30, 2014, 09:58:49 pm
Yes, solo 665=6400, 675=7300, 681=7900
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on June 30, 2014, 10:27:11 pm
How's it going Adam?

681 has the decomp in the top.......but the timing numbers are the same.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on June 30, 2014, 10:40:45 pm
Thank you Randy, you saved me 246$.

Thanks for your open communication
KilliansRedLeo
Tim Holcomb
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on June 30, 2014, 10:44:13 pm
Thank you Randy, you saved me 246$.

Thanks for your open communication
KilliansRedLeo
Tim Holcomb

Thats what went through my mind too.  Knew you hadnt ordered it yet due to Holiday there.

Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on June 30, 2014, 11:04:25 pm
Randy, all is good!
Hope you 're well too!

Adam
Title: Re: Dolmar 7900 Porting Info
Post by: man of stihl on July 01, 2014, 05:40:22 am
This is some good info here guys. Thanks
Title: Re: Dolmar 7900 Porting Info
Post by: farmboy on July 01, 2014, 10:08:24 pm
Yes, solo 665=6400, 675=7300, 681=7900
There are some differences 665 cyl is quad port where 6400 is open.
Shep
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 01, 2014, 11:18:40 pm
Yes, solo 665=6400, 675=7300, 681=7900
There are some differences 665 cyl is quad port where 6400 is open.
Shep

Didnt know that.   Thanks for tidbit.   I did know open 6400 just not the 665 info.
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on July 01, 2014, 11:44:04 pm
That's cool. Be interesting to compare the solo jug to 6400
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 01, 2014, 11:46:34 pm
I was thinking the same thing Adam.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 02, 2014, 07:48:15 am
Me too but short of buying an entire saw I don't know how we could get one to look at. Hmmmm, I think Shep (farmboy) just mentioned on the phone the other day that he converted a 665 to a 681! Perhaps he still has the 665 jug! I'll give him a call, perhaps he will have a look for us.
Title: Re: Dolmar 7900 Porting Info
Post by: farmboy on July 02, 2014, 07:55:29 am
I do still have it.  It in one of the PC drawers.  Actually the bottom drawer, left side, second row.  Be glad to get it out for ??.  Do remember the casting is Mahle 52ZNxxx, it's heavy they used the same basic casting for for 52mm punched hole 47mm IIRC.  Walls are thick, transfers are tiny both upper and lower.  I am gonna have to get a camera and learn how to use it.  I would send it for inspection pay return ship or make me an offer I can't refuse LOL. 
Shep
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 02, 2014, 08:38:48 am
Shep, I'll take it if it is a complete C/P. Send me a PM, I'll shoot you some $.

Tim
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 02, 2014, 09:16:20 am
Damn......too slow. lol

The 6400 is one jug that I've yet to be really happy with the gains I get.

Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 02, 2014, 09:32:19 am
Damn......too slow. lol

The 6400 is one jug that I've yet to be really happy with the gains I get.





OK, Randy, if I can find a 665 I'll send the whole mess to you to play around with, or just the jug your choice. Let me know!
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 02, 2014, 09:35:28 am
Cool........but remember.

I'm really slow.........but my shitty work makes up for it.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 02, 2014, 09:47:22 am
OK, here's a thought. All the Solo versions used the stroked crank. Putting the Solo jug directly on a 6400 that did not use the stroked crank would surely make a difference in the timing, good/bad I don't know. I suppose it depends on how Solo adjusted for the longer stroke, e.g. did they use a spacer, make the jug taller or mess with the piston?

To my way of thinking if they made the jug taller, putting it directly on a 6400 bottom end would have the timing waaaaay off. So, if they used a spacer then putting it on a 6400 bottom end may work out better. Also wondering what they may have done to the 665 piston to compensate for the increased stroke.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 02, 2014, 09:49:55 am
Cool........but remember.

I'm really slow.........but my shitty work makes up for it.

No one is in a hurry, this kind of stuff is fun, so sharing the fun and waiting to see what happens is part of the fun!
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 02, 2014, 09:52:09 am
I wonder if the Solo case is different? Higher at the jug mounting base.....
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 02, 2014, 10:07:26 am
Good thought, I do not know but I'll bet Shep does. I have looked round for a reliable way to measure deck height but have not found one. Also, Shep said ports are smaller on the Solo jug so perhaps they did that because of skirt width on the piston they used, although that seems to be takin' the long way home.
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on July 02, 2014, 10:50:21 am
I wonder if the Solo case is different? Higher at the jug mounting base.....

If it was then there would be no need for a spacer with the AM kits.  I think the cylinder has to be slightly longer.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 02, 2014, 10:53:04 am
You might be dead right Shawn.......and what you are saying makes sense.

The timing numbers between the 681s I've done and the 7900s are the same though......

Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 02, 2014, 10:56:33 am
Shawn, I agree with Randy they very well may be, since in order to use a Dolmar BBK on a solo you have to use the spacer. Deal is did they just make the cylinder base thicker or is the bore depth actually slightly deeper on the Solo jugs.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 02, 2014, 11:02:14 am
I wonder how close the 665 cyl looks to this 65cc cyl I have for 2 poulans. 

I do love the quad ports for these saws best so far.

Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 02, 2014, 11:04:40 am
A thicker base flange on the Solo jugs would possibly explain why Randy gets the same numbers on both 7900 and 681 saws.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 02, 2014, 11:19:22 am
It took me three tries on the same 681 to get the gains I was hoping to see.

I trashed the first top end, then tried a 272 piston, then just got a new OEM top end and started over.

That saw has so much torque stock, that it can be difficult to get big gains in a work saw type build.

I finally make a saw I was proud of from it........and learned a bunch in the process.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 02, 2014, 11:25:07 am
Nate username here solo. Has a stock strong 681 he runs in 5ci stock saw races. He has had another racer ( the guy is sort of a dickhead as I know him after meeting at races )  challenge him and his saw at race after winning with it again.
Causing the 681 to be opened up and checked for any work.   Yep it was stock.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 02, 2014, 11:31:26 am
Solo 681 hot saw running pump gas, 6 transfer port design, cutting a 20" pine round with non race chain.  Out west I think

http://youtu.be/HCB-zxFdXAQ
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 02, 2014, 11:33:39 am
Any other 681 videos I am going to post down in that solo 681 thread.  Unless I find Nate's stock saw run.
Title: Re: Dolmar 7900 Porting Info
Post by: adam32 on July 02, 2014, 11:58:24 am
Kevin, that saw is built by Mark Eckhardt out here in California.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 02, 2014, 12:01:37 pm
Kevin, that saw is built by Mark Eckhardt out here in California.

Seen the last name on videos but didnt know for sure. Thanks. 

I just posted some video of a alky nitro 3120 he is tuning now too.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 02, 2014, 12:05:37 pm
Saws for racing are not something I'm at all interested in.

One of these days I might try again to get into that......but I can't ever see me liking that stuff.
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on July 02, 2014, 12:40:54 pm
Saws for racing are not something I'm at all interested in.

One of these days I might try again to get into that......but I can't ever see me liking that stuff.

Same here... but I'm starting to get more extreme on work saws.  Strokers, different carbs, and a little added material here and there to the jug. 
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 02, 2014, 05:40:38 pm
A thicker base flange on the Solo jugs would possibly explain why Randy gets the same numbers on both 7900 and 681 saws.

Still trying to figure out how Solo compensated for the 1mm increase in stroke without using a spacer. They could have increased the thckness of the cylinder base, the actual bore in the jug is deeper, or perhaps they did something to the piston. At this point we do not know.

Just going by the BB7900 aftermarket cylinder kit.   Goes on 7900 without anything special at base bolt on.
681 uses 1.5mm spacer to work on 681. That tell me the extra must be on the cylinder. Just my WAG.




Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 03, 2014, 09:40:10 am
Just came across two NOS Solo 665 power heads. Don't know what I an going to do with them yet but I promised to send one off to Randy for him to play around with, I know what is going to happen with one. Want to see if Randy can get more out of the quad port closed cylinder than the OP Dolmar 6400.

My source still has a few left if anyone is interested but I believe less than 10 left. No 675 or 681 saws are available!
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 03, 2014, 09:50:20 am
Send me one to play with......and I'll send it back when I'm done for you to compare to the stock one.

What is the price on one????
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 03, 2014, 10:33:38 am
Randy PM sent, I will need an address to ship the saw to. I may also ship another 665 jug in case something bad happens or you want to try more than 1 idea!

Tim
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 03, 2014, 10:35:58 am
Replied to...
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 03, 2014, 10:48:27 am
I purchased 2 units that will be shipped today via UPS. When they arrive I'll stick my inspection camera down the plug hole and get some pictures of the ports and post for all to see!
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 03, 2014, 10:57:46 am
Cool.

With the 6400 the port timing numbers that make a strong runner are way different than the 7900. With a closed port jug......those numbers will likely be more in line with the 7900.

Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 03, 2014, 11:10:17 am
IIRC the 665 uses a 47 or 48mm piston, so lots of room to use wider skirt pistons. Shep mentioned that the stock ports on the 665 were quite small compared to the 675/681 saws, so there may be lots of room to play!
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 11:14:03 am
Did  Shep send that 665 P+C to you too?  Like to see some pics of that inside too.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 03, 2014, 11:16:40 am
Wider than stock ports aren't as important in a worksaw as having the timing numbers dead on.

The MS661 I was not happy with was only 3 different on one port, than the one that I was very happy with......yeah, it matters that much.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 03, 2014, 11:18:35 am
Dammit guys......I've missed being able to talk port work with someone that understands it.

Kevin......is there a sub forum for port work of all brands, or just the brand related headings?
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 03, 2014, 11:23:59 am
Randy, I'm sure Kevin will be along shortly with an answer to your question. AFAIK, there is not a specific place for those kinds of discussions. May be outside the premise of the site, but only Kevin can decide that.

Kevin, I'm sure that Shep will send it but it is hard for him to get to the post office so may be a while before it arrives. When it does, I'll get pictures and post. I'm going to send Randy a complete saw and the jug from Shep JIC or perhaps Randy may have more than one idea he wants to try!
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 11:25:37 am
Randy there used to be and there can be again. Just say the word and I can make a ported board again.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 03, 2014, 11:29:32 am
All the guys that really knew their stuff have left AS.......

There are some damn knowledgeable guys on BS......but port work really isn't of interest there.

To be honest though.......I'm so busy porting saws, that talking about ported saws is low on the list of everyday events too I reckon.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 11:30:40 am
ported board made.  Now it is up to your fellers to fill it in.  http://chainsawrepair.createaforum.com/ported-work-race/

Under the shin board in chainsaws.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 03, 2014, 11:31:20 am
Well, it would be sort of 'a busman's holiday'!
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 03, 2014, 11:31:31 am
Kevin, I'm leaving in the morning.....I won't be back till the 13th.

Let's talk about this when I get back.

I'd hate to see you kick something like that off and me bug out on you.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 11:33:21 am
No worries here. This site is so flexible to THE MEMBERS needs.
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 03, 2014, 11:37:56 am
I'll contribute when I get back home K.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 03, 2014, 11:42:05 am
Randy, travel safely, there will be a lot of coo coo clocks out there this weekend!
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 11:48:44 am
Where you heading Randy if I may ask.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 11:50:30 am
Should I move this thread to the ported board?
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun on July 03, 2014, 12:08:00 pm
Moved ported to top instead of under Shin for now. Till folks get used to it.   

I usually keep the top 3 reserved for the top 3 posted in boards of chainsaw brands.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 03, 2014, 12:10:43 pm
Move the thread to the ported board
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on July 03, 2014, 12:13:05 pm
All the guys that really knew their stuff have left AS.......

There are some damn knowledgeable guys on SawHawgz......but port work really isn't of interest there.

To be honest though.......I'm so busy porting saws, that talking about ported saws is low on the list of everyday events too I reckon.

It's hard to cut through the BS on SawHawgz, not that I don't like the banter, but it makes it hard to have a serious discussion. 

Should we make a thread to discuss porting tools?  Your favorite burrs/bits, handpieces, ect.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 12:23:44 pm
All the guys that really knew their stuff have left AS.......

There are some damn knowledgeable guys on SawHawgz......but port work really isn't of interest there.

To be honest though.......I'm so busy porting saws, that talking about ported saws is low on the list of everyday events too I reckon.

It's hard to cut through the BS on SawHawgz, not that I don't like the banter, but it makes it hard to have a serious discussion. 

Should we make a thread to discuss porting tools?  Your favorite burrs/bits, handpieces, ect.

You guys are the ones that can share this stuff on tools to use etc.  Make the thread and have at it. 

Also dont forget to post the stuff you have to sell there, srcarr. Stuff works for me and my needs.
Title: Re: Dolmar 7900 Porting Info
Post by: adam32 on July 03, 2014, 01:52:18 pm
What's the price on the 665? I could use one for a 4 cube saw :)
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 02:09:32 pm
Bore on a 6400? 
Title: Re: Dolmar 7900 Porting Info
Post by: Mastermind on July 03, 2014, 02:10:07 pm
Where you heading Randy if I may ask.

I'm going to work at a Sundance Kevin.

There is one that I attend that is in it's 38th year.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 02:13:45 pm
Found it.  6400 47

Solo 655 675 681 specs.



65,9
74,6
80,7
Bore / stroke mm 47 / 38 50 / 38 52 / 38
Max. power at rpm kW / rpm
3,6 / 9.500
4,3 / 9.500
4,7 / 9.500
Max. torque at rpm Nm / rpm 4,3 / 6.000 4,8 / 6.500 5,3 / 6.500
Max. permissible speed rpm
no load with cutter
13.500
13.500
13.500
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 02:25:34 pm
What's the price on the 665? I could use one for a 4 cube saw :)

Make sure legal with just being over the 4ci by a hair

665   =  65.955 

 4ci = 65.548   You know how some shows can be.



Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 02:36:08 pm
Racesaw for 4ci I think would be neat is a 48mm 36stroke 415 425 poulan.     Besides the husky 365. 

415 425 65.170 

Jerry has one with a 77cc 475 top he runs in 5ci classes.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 03, 2014, 02:38:00 pm
Where you heading Randy if I may ask.

I'm going to work at a Sundance Kevin.

There is one that I attend that is in it's 38th year.

Is that one of those music festivals?  That would be cool music if like that last one you posted about.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 04, 2014, 11:40:18 am
What's the price on the 665? I could use one for a 4 cube saw :)

Adam, I was quoted $479 each saw plus shipping to me and then there would be shipping to you. So the cost to your would be 479+ship to me+ship to you! I have no profit in these saws, just wanted to pass the deal I got on to others and recover my costs.

I spoke to my source and bought the rest of them also, so I may have perhaps 9-11 new in box saws coming.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 04, 2014, 11:48:45 am
Great price Tim.  Are those the ones the dealer had in NY?
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 04, 2014, 12:31:58 pm
No, Kevin, those saws all went to a tree service someplace down south! The NY dealer, wanted MSRP, too rich for my blood!

These came from a small distributor in the pan handle of Nebraska. Not enough trees in western NB to support a thriving chainsaw business. I just figured I could help him out a pass the deal I got on to others who were interested. Randy, wants one for himself, plus I going to send him 2-3 to port and play around with.
Title: Re: Dolmar 7900 Porting Info
Post by: adam32 on July 04, 2014, 01:11:30 pm
I'll probably get one too
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 04, 2014, 01:46:11 pm
I only have a limited number of these. So if you are interested send me a PM with your address so that I can get you a final cost. It will then be first come first served. The saws are up on another site also.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 05, 2014, 11:37:19 am
The 7900/681 C/P I got from Greece arrived today. Not bad AClarke not bad at all! I'll put some pics up later today. Only problem (for use on a Solo) is it has the decomp on the side like 7900, not on the top like Solo. So would have to use Dolmar plastic or redneck it and cut another hole. Still not a bad deal for $100. OBTW came in a white unmarked box, no marks of any kind on casting.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 05, 2014, 11:44:49 am
Just cut a hole IMO if for solo saw or NO decomp with plug.
But make sure you line up right. I somehow got it off a hair on my wild thing 505 cover and had to go bigger so the decomp wouldnt hang.  So simple yet I fubarred it. 
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 05, 2014, 11:53:58 am
Yeah I was trying to figure out how to get the hole in the right place. I'll go with a plug!
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 05, 2014, 12:27:39 pm
Here are pictures of the 7900/681 C/P kit from Greece. Nicely done no burrs, no flaws in the plating that I can see. Actually a pretty nice set.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 05, 2014, 12:32:46 pm
Inside the Jug
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 05, 2014, 01:31:59 pm
I take it no spacer comes with these one either for use on a 681? 
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 05, 2014, 02:22:24 pm
Correct, what a shame! Adam Clark said he could machine some up when he gets time. So, testing it will just have to wait. Sold the last 7900 I had a couple of days ago! I compared it to a Raisman Platt 365SP jug I have and would be willing to bet that is where it came from. It also feels a little more heavy than a stock Dolmar OEM 7900 jug but I need a new scale mine STB.

Oh and Shep is sending the 665 take off jug and a 6400 jug also.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 05, 2014, 02:28:52 pm
cool


got tired of looking at that big grin lol
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 05, 2014, 03:06:10 pm
I'll post some pics of both the 6400 and 665 jugs when they arrive for all to compare.
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on July 05, 2014, 07:50:38 pm
Tim,
just pulled the Greek cylinder from the 7900 to see how things look after a few tanks and all is good! Be cool to do a long term test with these AM cylinders and pistons
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 05, 2014, 08:06:03 pm
Bet your workers could put some run time on one in a hurry eh Adam.     ;)
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on July 06, 2014, 12:51:31 am
Yeah, in short order! ABUSIVE SOB's.  Hahahahahaha
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on July 06, 2014, 12:54:06 am
Tim. Any sort of markings on the Raismann Platt jugs?   Taiwan mfg?
Title: Re: Dolmar 7900 Porting Info
Post by: 660magnum on July 06, 2014, 02:03:32 am
Brazil

http://www.raisman.com/about-us/

http://www.raisman.com/light-construction/default.aspx?id=207
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 06, 2014, 08:44:52 am
Well RP sources stuff from all over the world. That being said, metallurgy is Brazil is some of the best in the world, not to mention Brazil is one of the largest aluminum producers in the world. There are NO marks on any of the components in the kit, has what appears to be a ductile iron ring (black), no split groove though. Decent earless circlips. Only mark on the piston is the EP arrow. Ports are nicely finished, and beveled, exhaust and intake spigots are nice and smooth, no casting flash anywhere. Looks to me to be virgin aluminum, no dark gray recast color to it.

Going to put it on an older Dolmar 7300 and run the snot out of it for this years shop firewood, so we will see what happens.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 06, 2014, 10:01:23 am
Adam, take a close look at the port pictures. I looked for bad spots in the plating on the dividers and above the ports but did not observe anything but I don't know exactly what you saw so, was shooting in the dark.

Also the plating and finish is way above that of the only Hutzl (Chinese) jug I have messed with in simple words the Hutzl jug is junk in comparison. Take a look at the squish band area on the Greek (for want of a better name) IMO it is on a par with what I see from Mahle on the new OEM cylinder I have.

I can't speak accurately of who made this jug but it is WAAAAY better than any of the other no-name stuff I've seen.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on July 06, 2014, 10:15:43 am
Tim for the  nice full wrap 372   http://www.prosafetyproducts.com/Products.html
Title: Re: Dolmar 7900 Porting Info
Post by: farmboy on July 06, 2014, 12:10:10 pm
Yeah I was trying to figure out how to get the hole in the right place. I'll go with a plug!
There was an indentation in my 665 cyl cover where the side decomp would be.  Cut it out looks like it came that way.  Had to put a brass washer on the Husky decomp it bottomed out before it tightened up in the 7900 cyl.  I didn't try the Solo top decomp my deep well wouldn't go down deep enough to remove it.  KRL is getting it in the 665 cyl.
Shep
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on July 06, 2014, 02:42:34 pm
Tim, you are correct.  The small chromed area between the two transfer had a small horizontal line in the plating.  I polished it out with a craytex wheel and all is fine.  I looks to me as though there was a low spot there prior to plating.  I noticed the squish "band" is only on the back half of the jug (intake side) this creates an area of higher squish velocity on the back side and poor squish velocity towards the exhaust.  Not ideal but it could be machined or improved with some sand paper on a mandrel.  Or just left!!! Lol.    I'll post a pic of the piston shortly
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on July 06, 2014, 03:05:22 pm
piston from the AM 7900 jug.  Proper squish band would likely create a more complete burn if it was cut evenly. weird step on intake side   Whats yours look like Tim?

(http://i1184.photobucket.com/albums/z329/Aclarke123/Mobile%20Uploads/DSC_0922_zps9bde9542.jpg) 


Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 06, 2014, 03:55:54 pm
Adam, do you want to know what the squish band looks like or the piston. Don't have any after being run pictures because kit is not on a saw yet.
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on July 06, 2014, 11:04:48 pm
Tim, I'll look at your cylinder pic again, but my cyl. has crescent shaped band on the FRONT of the squish band.  Kinda odd... Never seen that but it looks like it may be machined in?
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 07, 2014, 09:47:27 am
Adam, after looking very closely and doing some quick measurements, mine appears to have the same measurement from spigot to squish on both the IP & EP sides perhaps within +/- 0.0005. It also appears that the combustion chamber is a little off center shifted toward the IP centered on the plug and then tapers gradually toward the EP. Looks to be done intentionally because as near as I can tell it is equal measurements L to R in the bore. I'll try to get a better picture for you.

OBTW all the remaining NOS Solo 665s are enroute, should all be here by Monday next.
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on July 07, 2014, 12:28:36 pm
Thanks for measuring your Tim.  After studying a few old stihl work Saw pistons last night I think the carbon pattern on the top of the piston indicates a pretty thorough burn that cools down towards the exhaust side. This is a good thing that the offset chamber contributes to. 
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 07, 2014, 12:43:21 pm
Yeah, now that you mention it, same thing was done on the Maico 250cc MX bike jugs or manbe it was the CZ?
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on July 07, 2014, 02:40:41 pm
Thanks for measuring your Tim.  After studying a few old stihl work Saw pistons last night I think the carbon pattern on the top of the piston indicates a pretty thorough burn that cools down towards the exhaust side. This is a good thing that the offset chamber contributes to. 

Generally the burnt locations are the hotter areas.  You'll have clean spots where the fresh a/f charge from the transfers cools and cleans the piston.
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on July 07, 2014, 03:58:15 pm
that makes sense, thanks for clarifying that   looked at two well used 046 pistons and a 660 and they are completely black minus a very small area where the leading edge of the transfer opens. Dolmar seems more limited to the center and exhaust side, perhaps the higher CC pressure through the tiny transfers helps?  thanks, Adam
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 07, 2014, 04:09:17 pm
You, know Adam, I spoke to Shep=Farmboy this afternoon and he mentioned the same thing, smaller CC volume plus tiny transfers=higher velocity of the incoming charge. When Randy gets back next week perhaps he will provide his thoughts. I'd really like to come up with some sort of plan to port a 665 but haven't collected enough info yet. Also got news from the Solo distributor this AM, he thinks he might have a 681 top end kit floating around. He said it did not have the decomp valve, don't know if that meant no valve or no provision for one. We will see supposed to call back later today or tomorrow.
Tim
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on July 07, 2014, 04:45:10 pm
that makes sense, thanks for clarifying that   looked at two well used 046 pistons and a 660 and they are completely black minus a very small area where the leading edge of the transfer opens. Dolmar seems more limited to the center and exhaust side, perhaps the higher CC pressure through the tiny transfers helps?  thanks, Adam

Completely black is bad... you want a piston with some wash similar to what you posed except more even from side to side.  It looks like the transfers are coming in at different angles and that is why it's not symmetrical. 

Overall your piston wash looks good, ignition timing is good, piston is the right temperature and your oil mix looks good because you have slightly more carbon buildup right under the spark plug and it lessens as you get towards the outsides of the piston in each direction because that is where the heat can be removed by the cylinder wall.  If you had a lot of carbon build up towards the ex side that would suggest late timing or too much oil and the gasses are still burning as they are going out the door. 

It being clean from the transfers all the way to the edge on the intake side suggest a good operating temperature, and that the fresh a/f charge is not leaving an ex pocket on top of the piston on the intake side which can happen with too steep of inlet angle in the transfers.

So like I said everything looks great except for the PTO side, I would like to see the line from the transfer divider like you see on the other side.  Something is messing with the flow from the transfer on the mag side closest to the exhaust port and causing it not to hit the top of the piston there.  It could be inlet angle, plating flash, or later timing then the other ports.
Title: Re: Dolmar 7900 Porting Info
Post by: jmester on July 07, 2014, 05:47:23 pm
+1 to srcarr52.
Title: Re: Dolmar 7900 Porting Info
Post by: KilliansRedLeo on July 07, 2014, 06:23:00 pm
+2
Title: Re: Dolmar 7900 Porting Info
Post by: farmboy on July 07, 2014, 10:21:49 pm
Just for info the metal insert for the 7900 intake boot and the Husky 372 is a swap.  When I converted my 6401 to a 7901 I found the insert missing when I tore it down used the 372. 
Shep
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on July 07, 2014, 10:40:18 pm
Thk guys.  That pic is the stock AM jug.  Ported the Saw and cleaned up the piston.   Gonna run it tomorrow and will take pics of the crown for kicks when I pull it down...
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on September 23, 2014, 07:03:57 pm
I just measured up a stock 7900 and I got these numbers.

Squish 0.025"
Ex Dur 148
Tr Dur  96
In Dur  151
Blowdown 26

I'm thinking

-0.040" on squish
Squish 0.020"
Ex Dur 159
Tr Dur  104
In Dur  159
Blowdown 27.5

I know people have mentioned that they like lots of blowdown, probably because of the small crankcase volume, but what is a lot?  To me... stock is a lot.
Title: Re: Dolmar 7900 Porting Info
Post by: mdavlee . on September 23, 2014, 07:43:59 pm
27-30 works. I'm going to do 3 more here soon and will have more info for what worked better.
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on September 23, 2014, 08:46:53 pm
 7900 seems to be temperamental in regards to keeping port velocities up, especially intake and transfers.  Big carb and opened up intake killed the power on the last 7900  I experimented with.   Added some epoxy and much smaller carb and it came alive again.   
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on September 23, 2014, 11:40:54 pm
7900 seems to be temperamental in regards to keeping port velocities up, especially intake and transfers.  Big carb and opened up intake killed the power on the last 7900  I experimented with.   Added some epoxy and much smaller carb and it came alive again.   

I don't think it's a port velocity thing, I think it's either the small time area of the ex port because of the piston width or the transfer port charge is to explosive and causes too much mixing so you need to give it as much time to let as much exhaust out as possible. 
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on September 24, 2014, 09:57:58 am
The saw I was referring to  is a race saw that's had the port time area opened up and velocity through the intake in particular was too slow with the .945 venturi carb that was on it (hl360).  The fuel signal on the main jet was poor and it didn't atomize in the venturi as you would normally see.  Added a screen to the main jet which helped but in the end the carb was too big.  Smaller .750 venturi was a huge improvement.   Seems to me that the stock ports have been optimized for tight/high crankcase pressure , hence the tiny transfers with relatively long blowdown to minimize loss through the exhaust.   
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on September 24, 2014, 10:07:33 am
The saw I was referring to  is a race saw that's had the port time area opened up and velocity through the intake in particular was too slow with the particular .945 venturi carb that was on it.  The fuel signal on the main jet was poor and it didn't vaporizer is the venturi as you would normally see.  Added a screen to the main jet which helped but in the end the carb was too big.  Smaller .750 venturi was a huge improvement.   Seems to me that the stock ports have been optimized for tight crankcase pressure , hence the tiny transfers with relatively long blowdown to minimize loss through the exhaust.   

A .945 venturi is too larger for the 20 hp honda GX200 motors I build.  I stick with the 334WXA which is .75" I think. 
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on September 24, 2014, 10:25:32 am
Using an HL306 now.  Have you experimented with the old traditional style HL venturi vs newer infinite radius design ? 
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on September 24, 2014, 11:01:37 am
Using an HL306 now.  Have you experimented with the old traditional style HL venturi vs newer infinite radius design ? 

I've only messed with the newer 334, 304, and 384.  The only reference I've ever heard to infinite radius was with the velocity stack design.
Title: Re: Dolmar 7900 Porting Info
Post by: 660magnum on September 24, 2014, 11:14:34 am
I have a couple stock 7900's. I like them the way they are but there's a guy South of town that has a old style woods ported 7900 by EHP and it runs much stronger than my two 7900's but doesn't hold a light to my Brent Combs 066.
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on September 24, 2014, 11:17:11 am
I have a couple stock 7900's. I like them the way they are but there's a guy South of town that has a old style woods ported 7900 by EHP and it runs much stronger than my two 7900's but doesn't hold a light to my Brent Combs 066.

Comparing a 7900 to an 066 is like comparing apples to steak.  It's not even in the same category. 
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on September 24, 2014, 05:50:42 pm
Infinite radius does not have the traditional radiused ring to create the venturi. Instead, the main jet is placed at the smallest diameter of the gradually sweeping radius machined into the throat of the car, it Looks totally smooth.  I really don't think this new Infinite radius design provides a strong and sudden pressure drop as needed to atomize fuel well at low to mid rpm. Just speculation, but I can't see this working well at less than max rpm.  I'll see if i can find a pic or drawing
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on September 25, 2014, 10:37:35 am
Infinite radius does not have the traditional radiused ring to create the venturi. Instead, the main jet is placed at the smallest diameter of the gradually sweeping radius machined into the throat of the car, it Looks totally smooth.  I really don't think this new Infinite radius design provides a strong and sudden pressure drop as needed to atomize fuel well at low to mid rpm. Just speculation, but I can't see this working well at less than max rpm.  I'll see if i can find a pic or drawing

Ok, I understand what they are and I agree with you.  It's the same problem I have with the 304 and the 384 or any bored out carburetor. 

The low pressure region created by the venturi or lack there of is too weak to meter the fuel correctly.  Instead these carbs rely more on you setting the pressure of the needle (ultimate the fuel pressure under the diaphragm) correctly to change the full throttle mixture.  Everything else besides WOT and idle are pretty much worthless. 

The venturi is not only creating a low pressure region to atomize the fuel but it's also creating an area where the pressure is directly related to air flow (engine demand).  Since this area is the outlet for the fuel it changes the fuel flow based on engine demand.  No contraction (venturi) no engine demand fuel metering, well I shouldn't say no, but much less and unstable.

For instance I took a stock briggs 5hp carb (straight bore design) and modified it by boring only the inlet and exit to create a venturi, it picked up around 2hp on my dyno on a engine that produced 10hp with the stock carb and 14hp with a tilly 334.
Title: Re: Dolmar 7900 Porting Info
Post by: mdavlee . on October 06, 2014, 07:52:42 am
I degreed a 7910 cylinder today and a 7900. The 7910 had 2 degrees less exhaust. It was at 107, 132, and 80. 7900 cylinder was 105, 133, and 80 as it sit on the case with the spacer and 46 piston.
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on October 06, 2014, 09:15:48 am
Surprising to see the exhaust at 107 even with the jug raised for the 046 piston.  Be cool to see how it pulls as is.
Title: Re: Dolmar 7900 Porting Info
Post by: mdavlee . on October 06, 2014, 09:33:12 am
The piston didn't change exhaust timing any from what I can tell. It does add intake timing. I could pop the other one together with that top end and see how it does vs the ported one.
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on October 06, 2014, 11:12:06 am
I finished one over the weekend.

https://www.youtube.com/watch?v=QiV4ZNpp7mc&list=UUXC1J6DgW1vZD7RmETluaNQ
Title: Re: Dolmar 7900 Porting Info
Post by: mdavlee . on October 06, 2014, 01:00:28 pm
Sounds good Shaun.

Smurf #1 ready.
Title: Re: Dolmar 7900 Porting Info
Post by: Cut4fun . on October 06, 2014, 01:36:53 pm
I wonder how this new topend 7901 compares to the old 7900 topend. 

I was wondering why the exhaust looked totally different stepped  ??? and decomp in solo location. So new top covers on 7901 like solo covers?
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on October 06, 2014, 01:40:38 pm
Mike. What are the differences in ports 7901 vs 7900 jug?
Title: Re: Dolmar 7900 Porting Info
Post by: mdavlee . on October 06, 2014, 05:44:03 pm
I'll try to throw the new top end on the other one I'm doing the swap on tonight. I have my stock one to use as a baseline.

The exhaust is stepped because of the slr muffler. It goes all th

e way into the step. I may use it as a anti reversion step instead of blending it all the way in.

The ports look the same size. If I had dilly putty I could mold them.
Title: Re: Dolmar 7900 Porting Info
Post by: mdavlee . on October 06, 2014, 06:27:11 pm
http://youtu.be/KB3cnnJf23E
Title: Re: Dolmar 7900 Porting Info
Post by: aclarke on October 06, 2014, 09:11:15 pm
Looks good, sounds crisp!!
Title: Re: Dolmar 7900 Porting Info
Post by: mdavlee . on October 06, 2014, 09:15:31 pm
Thanks. It's blowing 170 lbs right now on tank 1.
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on October 07, 2014, 10:35:39 am
Thanks. It's blowing 170 lbs right now on tank 1.

That's where mine ended up. 
Title: Re: Dolmar 7900 Porting Info
Post by: mdavlee . on October 07, 2014, 10:43:07 am
That's where mine ended up. 

I think that's about right for a working saw. I have used some that had more but they sometimes get a little hot in long bucking cuts.
Title: Re: Dolmar 7900 Porting Info
Post by: srcarr52 on October 07, 2014, 11:48:05 am
That's where mine ended up. 

I think that's about right for a working saw. I have used some that had more but they sometimes get a little hot in long bucking cuts.

I have had 288's and 394/5's that had over 200 psi and I used them to mill with but the 7900 may be a different animal.
Title: Re: Dolmar 7900 Porting Info
Post by: 660magnum on October 07, 2014, 12:09:43 pm
I have a year 2006 7900 with 180 #. I bought it used and it is stock as far as I can tell. It appeared to be a commercially used saw when I got it. (Beat up).

I've since replaced all the damaged parts and updated all components to the 2010 era 7900's. I haven't bothered the P&C. It has always run nice for me and doesn't get hot. 
Title: Re: Dolmar 7900 Porting Info
Post by: mdavlee . on October 07, 2014, 03:49:17 pm
I have had 288's and 394/5's that had over 200 psi and I used them to mill with but the 7900 may be a different animal.

I've had one high compression saw keep going on me. I had to push in the decomp and hold it in to finally kill it. The ignition did nothing. I'm a little gun shy of 200+ lb work saws.
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on October 16, 2014, 08:29:29 pm
I'm just guessing but think that 7900 was a 7900 Jerod sold him quite a few years ago like I'm guessing but 10 or more years ago and I'm thinking Jerod ran the saw for a while first , I built a bunch of those 7900's like that saw and they are not cookie cutters , they are true worksaws and were never meant be be hot in power . Jerod was sending 7900's to Javilin so he wanted very good long lasting motors which they were , I cannot remember how many 7900's I built for them but do remember having pickup truck full of saws on each trip he made north to me . The 7900 can be made quite abit hotter than how those saws ran
Title: Re: Dolmar 7900 Porting Info
Post by: 660magnum on October 16, 2014, 08:42:50 pm
It was a early one for it had a red cover, no top AV spring limiter cap, and a straight chain catcher tab.
Title: Re: Dolmar 7900 Porting Info
Post by: EHP on October 17, 2014, 11:42:53 am
its pretty easy to know when you got the 7900 pulling good , it will pull the choke  on when wide open so you have to either put one more turn tighter on the spring on the choke shaft to stop it from coming on or a double spring setup on it , yes at that point the 7900 motor is moving alot of air threw it