Chainsaw Repair

How To Basics - Carb Fixes + Mods - IPL and Service Manuals => How To Basics and Fixes => Topic started by: jmester on February 14, 2013, 10:05:39 pm

Title: Port timing.
Post by: jmester on February 14, 2013, 10:05:39 pm
When you raise or lower port timing what are to gains to the saw. I know that when you raise them you get more rpms. And if you lower them you get more torque. Can you raise the exhaust and lower the intake or vise versa. Any help would be appreciated.
Title: Re: Port timing.
Post by: 660magnum on February 14, 2013, 10:10:11 pm
Just widen the port
Title: Re: Port timing.
Post by: jmester on February 14, 2013, 10:21:26 pm
I am trying to learn what happens. As a result of raising or lowering port timing weather intake,exhaust or transfers. I know that you can widen them and get more flow. Just trying to figure it out. So I can play around with some timing and porting
Title: Re: Port timing.
Post by: aclarke on February 14, 2013, 10:40:28 pm
changing the port timing will change the rpm range where the saw makes power.  Generally, the more duration the higher the peak rpm/power levels.  Timing (duration open) and port area requirements need to be met to produce a given level of power. you can change the aree, i.e widen ports, to a point to achieve the desired results, but ultimately the duration will have to be increased as the port width jeopardizes ring life after a certain point. 
Title: Re: Port timing.
Post by: 3000 FPS on February 14, 2013, 11:26:25 pm
If you raise the exhaust port to get higher rpm  you cut down on the compression and you loose torque. 

 I would rather drop the cylinder alittle to increase the compression which will increase torque and widen the ports to help flow of the gases which will increase torque and muffler mod it and advance the timing by 3 to 4 degrees to increase torque.   Then I have a saw that does not lose as much rpm when in the cut because of all the torque.
Title: Re: Port timing.
Post by: jmester on February 15, 2013, 06:42:37 am
That makes sense. If you mill the base to raise the compression, do you go back and make your porting numbers the same as before you milled it. Or is that the point to drop it down and get more comp and torque. I guess that is where I have to do some trail and error. Also what about the tranfers?
Title: Re: Port timing.
Post by: 660magnum on February 15, 2013, 07:29:50 am
When dropping cylinders, you must keep into context the piston skirt length and the possibility of free porting the engine.

Everything is a interrelational compromise.
Title: Re: Port timing.
Post by: jmester on February 15, 2013, 07:33:13 am
So that there is no overlap in openings correct. Like the exhaust being open when the intake is open.
Title: Re: Port timing.
Post by: 660magnum on February 15, 2013, 07:53:46 am
Free porting is when the skirt of the piston rises above the bottom of the exhaust port allowing the crankcase cavity to vent to the atmosphere.

This is not considered a good trait but some engines can tolerate some mild free porting.
Title: Re: Port timing.
Post by: Al Smith on February 15, 2013, 08:59:09 am
Generally speaking if you raise the rpm range the port time area open will require some adjustment .In simple terms as the time deceases the area must increase because you can only shove a certain amount of fluid or gas  through a certain sized hole in a given amount of time with a given amount of pressure .

Another thing to keep in mind is with port loop scavenging on a two cycle engine is it starts and ends in atmospheric pressure .It's the differentials of pressures within that complete cycle that determines the flow within regarding pressure changes .--clear as mud --
Title: Re: Port timing.
Post by: Al Smith on February 15, 2013, 09:14:37 am
Now free porting ,kinda deep .There is a phenominan termed resonant frequency which is used on tuned exhausts but also has been attempted on intake circuits .The only example I ever heard of that worked commercialy was one model of Villers motorcycle made in England probabely 50-60 years ago .I don't think they were totally successful or else they'd still be in business .

Theoretically what you have is at one small portion of the cycle where all three ports ,intake, transfer and exhaust are open drawing fuel directly from the carb .Complete purge of the incoming  charge .Coupled with a tuned exhaust it is a two cycle tuners degree of utopia .The theoretical  push pull circuit .Problem is at least so far nobody has been able to figure it out successfully because the RPM band it would work at is extremely narrow .Now that one is a bone to gnaw on .
Title: Re: Port timing.
Post by: 3000 FPS on February 15, 2013, 11:31:11 am
That makes sense. If you mill the base to raise the compression, do you go back and make your porting numbers the same as before you milled it. Or is that the point to drop it down and get more comp and torque. I guess that is where I have to do some trail and error. Also what about the tranfers?

I do not usually drop a cylinder that much to worry about the timing changing that much and so I do not change the timing usually.   If I am working on a open port transfer cylinder then I will shape the top of the transfer so that it is pointing more towards the intake without raising the transfer itself and affecting the blowdown.   This is done so that the charge coming up from the crankcase flows more toward the intake and hopefully allowing less of it out the exhaust while it is open.
Title: Re: Port timing.
Post by: Al Smith on February 15, 2013, 01:58:03 pm
It comes down to theories and personal preferences as what method is used .One method might prove to be as effective as another one .

For example I use a domed piston to alter the flow around the intake side of the piston combined with a widening of the transfer ports as well as longer blow down to more completely purge the residue of unburned products of combustion .Some prefer to use finger ports and a flat top piston to achieve the same end results .Nobody is right or wrong here in their approach if the end results work .

Some prefer to cut the entire bottom out of tunneled transfers .I prefer widening them and doing some flow work on the piston windows .

Really about the only way you'll ever get half way good at it is to do it .If it doesn't work so good find a different method .Don't start out with  a thousand dollar saw to experiment with .get a 50 dollar special .Listen ,ask questions ,ignore the idiots that poke fun at you .Armchair quarter backs that usually don't have the common sense God gave a goose anyway .Hang long enough it will come around . ;)
Title: Re: Port timing.
Post by: 3000 FPS on February 15, 2013, 03:10:58 pm
It comes down to theories and personal preferences as what method is used .One method might prove to be as effective as another one .

For example I use a domed piston to alter the flow around the intake side of the piston combined with a widening of the transfer ports as well as longer blow down to more completely purge the residue of unburned products of combustion .Some prefer to use finger ports and a flat top piston to achieve the same end results .Nobody is right or wrong here in their approach if the end results work .

Some prefer to cut the entire bottom out of tunneled transfers .I prefer widening them and doing some flow work on the piston windows .

Really about the only way you'll ever get half way good at it is to do it .If it doesn't work so good find a different method .Don't start out with  a thousand dollar saw to experiment with .get a 50 dollar special .Listen ,ask questions ,ignore the idiots that poke fun at you .Armchair quarter backs that usually don't have the common sense God gave a goose anyway .Hang long enough it will come around . ;)


  I like it.  Good Karma.
Title: Re: Port timing.
Post by: srcarr52 on February 15, 2013, 04:41:24 pm
I do not usually drop a cylinder that much to worry about the timing changing that much and so I do not change the timing usually.   If I am working on a open port transfer cylinder then I will shape the top of the transfer so that it is pointing more towards the intake without raising the transfer itself and affecting the blowdown.   This is done so that the charge coming up from the crankcase flows more toward the intake and hopefully allowing less of it out the exhaust while it is open.

I've made a lot of gains by changing my ways on the upper transfers.  It's all about creating a good wedge of new mix to push the spent gases out the exhaust without mixing much with the incoming charge.  That wedge has to push up the intake side wall and flush out the spent gases in the chamber before coming back down the exhaust side.  Direction of the inlet, paying special attention to where either side flows intersect, and staggering the ports from exhaust to inlet side opening and entrance angle can get you some real gains.  I find when this is working well running less blowdown than normal will gain you upper end power without killing the peak torque. 
Title: Re: Port timing.
Post by: jmester on February 15, 2013, 05:02:45 pm
Thanks for all the great  insight. That helps me grasp it pretty well. I think I am going to work on doing a woodsport on a 028.  Having trouble getting a good read on the tranfers. Any one know what degree they are. If you mill a base down. Should you run a gasket or not. Thanks again for sharing your knowledge.
Title: Re: Port timing.
Post by: jmester on February 15, 2013, 05:03:15 pm
It is time to play !
Title: Re: Port timing.
Post by: Al Smith on February 15, 2013, 05:15:00 pm
As a rule on an 028 being the same design as the 038 the transfer should open at about 20 degrees of rotation behind the stock opening of the exhaust port .This is an educated guess on my part because I've never done any port work on that model .Got one in the shed though to do some day .

Give you a little hint .They make a tiny thin high intensity LED pencil thin flash light that  takes AAAA batteries .It's small enough you can peer right through the spark plug hole and with no problem see when the ports start to open .Best light I've ever found .
Title: Re: Port timing.
Post by: jmester on February 15, 2013, 05:36:45 pm
I think to if I were to where my glasses that might help too, they are new to me, and I forget I have them. Does 101* for exhaust sound right. Who makes the little lite you made mention of. I know stylus made some small pen lights.
Title: Re: Port timing.
Post by: Al Smith on February 15, 2013, 06:50:31 pm
101 sounds right on the money referencing to 028 to an 038 AV.If that holds true the stock squish is probabley around 45-46 thou .If that's a fact you can safely drop the cylinder 20 thou or so .

If you are hesitant pull the base gasket which is around 20 thou and swear a coating of permatex number 2 which will seal it up enough to at least test it .Without raising the exhaust it should peak out slower but with a tad more torque on a test like that .

Don't get in a rush,take it a little at a time .You can always remove metal but it's a beech trying to put it back .

Another hint : if you only widen a port some what you have not changed the port timing although by dropping the cylinder without cutting the base you have .Now if you choose to cut the base and raise it back up to stock 101 you again have not changed the dynamics of the timing except you've increased the blow down duration  .If you raise it say 4 degrees you've effectively added 4 degrees more blow down more or less .

Remember though it's not totally liniar because of the angle of rotation geometrically speaking because of the position  of the crank throw with respect to the rod and piston position .Measure often and cut slow .If you have to slide the cylinder back on a half dozen times it's no big deal .Better safe than sorry .Rome wasn't built in a day and you can't report a saw in half an hour .
Title: Re: Port timing.
Post by: jmester on February 15, 2013, 07:23:38 pm
I got .040 for squish. I do have a domed piston. Would you still measure the squish the same. Duration is from TDC to when the port begins to open correct. I was thinking of having the base milled and running a gasket. So I would mill the base .040. Put gasket on and raise .020 and leave a squish of .020.
Title: Re: Port timing.
Post by: Al Smith on February 15, 2013, 08:13:16 pm
You take it from the highest point of the piston to the head deck . 20 thou would be right close because most don't say get any closer than 19 thou .Now is that 40 thou with the gasket in or out when you measured it .Now is that a cut domed piston commonly refered to as a pop up or is it a factory hemi dome like an 038 Av ?

I can ever seem to get the danged things right on any way for some reason .I've used everything to regasket them from a front cover of National Geographic to the cardboard from a case of Budweiser to adjust the spacing after I screwed it up .
Title: Re: Port timing.
Post by: jmester on February 15, 2013, 08:30:15 pm
It was .040 with the gasket. It is a factory dome.
Title: Re: Port timing.
Post by: Al Smith on February 16, 2013, 05:02:33 am
As I suspected then that being said if it has an offset combustion chamber meaning not concentric to the center of the cylinder it is a direct copy of an 038AV .Could be vica versa because I'm not certain which model was out first .

I've never taken the time to investigate what that 028 I have in the shed has .This has  caused my curiosity to arouse so I think I might just delve into it to see what design it uses . .
Title: Re: Port timing.
Post by: 660magnum on February 16, 2013, 05:21:46 am
The 026 has the off-center small dome in the combustion chamber also
Title: Re: Port timing.
Post by: jmester on February 16, 2013, 06:28:05 am
From what is can tell is the 46mm piston is domed. And  the 44 mm piston is flat topped. I hope this does not sound dumb, I would like to set the squish at .025 and run a base gasket of .020. If I am correct I think I would need to mill off .045. Or would it be to mill off .035 to get a .025 squish with a gasket.  I tried to measure the squish at or around the dome or highest point , there is plenty of room to drop it down. With out any clearance issues.
Title: Re: Port timing.
Post by: 3000 FPS on February 16, 2013, 11:33:31 am
I do not understand why you want to run a base gasket.   Just leave it out and you end up cutting much less from the base of the cylinder which is better.     If you use some yamabond or similiar sealant there will be no problem with the cylinder sealing up.
Title: Re: Port timing.
Post by: jmester on February 16, 2013, 11:46:14 am
I have used dirko before. But I like the way that if you have to pull it apart again it is a lot easier with a gasket than with sealant.  Imo.  I have used other things such as aluminum foil, cereal box with good results. Just like a gasket I guess.
Title: Re: Port timing.
Post by: man of stihl on February 16, 2013, 02:58:14 pm
I have used dirko before. But I like the way that if you have to pull it apart again it is a lot easier with a gasket than with sealant.  Imo.  I have used other things such as aluminum foil, cereal box with good results. Just like a gasket I guess.
I agree. if your going though the trouble of machining the cylinder base, i would use a gasket.
Title: Re: Port timing.
Post by: Al Smith on February 16, 2013, 07:27:50 pm
If you have 40 thou with a gasket and you want 25 you'd mill off 15 thou .If you went without a gasket, sealant would probabley squeeze down to 2 thou .So 40 minus 20 is 20 thou plus aprox 2 for the sealant would be 22 thou . 3 thou wouldn't make that much difference .I dont think it's exactly 20 thou on the gasket ,like .5 mm which is almost 20 thou .I'm kind of an SAE type guy this metric stuff is un American . ;D
Title: Re: Port timing.
Post by: Al Smith on February 16, 2013, 07:43:25 pm
You know come to think about it if you want 25 thou all you need to do is get a set of micrometers and start measuring paper thickness .Most printer paper is a tad less than 3 thou ,Some is close to 5 thou .An old fashion IBM type punch card is 7 thou .Lots of possibilities here .
Title: Re: Port timing.
Post by: jmester on February 16, 2013, 07:47:59 pm
I measured the gasket at .020 that came off the saw. Have a new one on the way. Will have to measure it to make sure. Is your .015 mill spec with or with out a gasket. I might check out some different stuff. I have been saving some different thickness of paper and card stock for a while.
Title: Re: Port timing.
Post by: jmester on February 16, 2013, 07:56:11 pm
I just found a index card that is .007 thickness. Should give me a squish of .027 which I can live with. I guess now I need to work on my porting work.
Title: Re: Port timing.
Post by: jmester on February 17, 2013, 08:26:18 pm
Will you get an accurate squish reading if the rings are removed. Or because the piston rocks back and forth it gives you the wrong reading. I ask because, I cut out my index card gasket of .007 thickness. And bolted the cylinder back up and got a squish of .035. It should be around .027 now with removing the factory base. That measured .020.
Title: Re: Port timing.
Post by: aclarke on February 17, 2013, 08:53:33 pm
Put the solder at 90 degrees to exhaust.  I.e. if exhaust is 12:00 put the solder at 9:00 and 3:00  the rocking is minimized at the axis
Title: Re: Port timing.
Post by: jmester on February 17, 2013, 08:57:59 pm
So the rocking does have an effect. I will try it  that way and see what I get.
Title: Re: Port timing.
Post by: Al Smith on February 17, 2013, 09:10:15 pm
You have to remember two things .First it's a hemi domed piston plus it's a off set chamber .You're going to have to get that solder where it hits the machined face  around  the chamber pretty square which is going to be tough being off set and a rounded surface of the piston face.

That same deal I might add is why and how I screwed up cutting down the base of an 038 Av and made a head knocker out of it which I had to correct with a thicker gasket .The whole concept  of what I just said had completely slipped my mind when I made my preliminary mesurements .Chit happens.


While on the subject I'm not certain if the chamber is milled perpediculer to the bore or angled .You could probabley check it with a depth micrometer from the cylinder base .Geeze what a fine kettle of fish this is .
.
Title: Re: Port timing.
Post by: jmester on February 17, 2013, 09:14:28 pm
I will check it in a couple of different places tomorrow and see what I get.
Title: Re: Port timing.
Post by: man of stihl on February 18, 2013, 08:42:19 pm
This is how i check squish. (http://i1102.photobucket.com/albums/g457/rjcfritz/490numbers012_zps72ac9bf6.jpg) (http://i1102.photobucket.com/albums/g457/rjcfritz/490numbers013_zpsa2de3ed6.jpg)
Title: Re: Port timing.
Post by: Al Smith on February 18, 2013, 08:58:03 pm
Well geeze you usually knock the carbon off first . ;D

I've been racking my brain on this hemi domed piston business becuse it would not be the same with an offset combustion chamber .About the only way or one way might be to squeeze wax and measure with a  good set of calipers from the piston skirt .

I don't know if it would work or not .You'd have to have the piston face clean enough the wax would stick and oil the head deck so it wouldn't stick .

Macdizzy mentioned using some kind  of wax or clay but exactly what kind or how to slips my mind .
Title: Re: Port timing.
Post by: jmester on February 18, 2013, 09:15:52 pm
I was looking through the plug hole and even with a dome and offset chamber it still has a squish band around the outer most circumference. I think that if I  check it at the 3 and 9 o clock position will give me the most accurate reading. You just have to make sure that your solder is tight to the cylinder wall. And the dome on the piston does not go to the outer edge in has a flat all the way around. But maybe I am missing it all together.
Title: Re: Port timing.
Post by: jmester on February 18, 2013, 09:20:24 pm
I wonder if mothers clay bar would work for what you are speaking of, sound kind of messy. Just imagine to much wax or clay with no rings big mess.
Title: Re: Port timing.
Post by: brokenbudget on February 19, 2013, 05:08:43 am
I wonder if mothers clay bar would work for what you are speaking of, sound kind of messy. Just imagine to much wax or clay with no rings big mess.

how are you going to get an accurate measurment from clay without it deforming? use the proper sized solder and put it at the 12, 3, 6 and 9-oclock possitions to hold the piston even. no point in over thinking this.
Title: Re: Port timing.
Post by: jmester on February 19, 2013, 05:44:51 am
I was throwing the idea out, from page 2. I think it is possible just make sure the clay does not stick to either side.
Title: Re: Port timing.
Post by: Al Smith on February 19, 2013, 06:05:46 am
I don't know if wax would work or not I just threw that out as a possibility .I use solder myself just like most people do .

In this praticular situation it should seem logical that the very center of the hemi domed piston would in fact appear to be where the measurement should be taken as that in fact is the closest the piston top would be from the head deck .

With that in mind what would happen if you used 5 pieces of soft solder about a 1/4" long .4 placed equadistant from the center of the piston at 12,3,6,and 9 o'clock with one piece dead center ,with a little dab of grease to hold them in place .Measure the center piece .

Know compounding the problem ,does the center of the piston align with an area you could mash the solder because the chamber is offset ? If not that theory goes right out the window .I don't know myself because I have nothing to base it on unless I tear down a saw with an offset chamber to verify that which I'm not going to do at least not right now .

Another thing ,is the head dead flat or does it have some curvature to it? Another answer I simpley do not have .I would assume flat .
Title: Re: Port timing.
Post by: jmester on February 19, 2013, 03:39:40 pm
Got the squish measured at .025, works well to go at 12,6,3 and 9. Have a question how do you figure out timing duration.
Title: Re: Port timing.
Post by: Al Smith on February 19, 2013, 05:27:29 pm
Duration is from the time the port opens until the time it closes .Get the exhaust through the exhaust port ,intake through the intake and transfer by peeking through the plug hole.

Then if you want you can figure time open in relation to speed and further figure time area open with a port map  to use some of the formulas .--or you could just wing it . Now a wing works pretty good if you don't go bonkers with it .

What you really should do is Google  three things .McDizzy ,A Bell and  Gorden Jennings ,Between those three they can answer just about any question there is about two cycle performance tuning .
Title: Re: Port timing.
Post by: aclarke on February 19, 2013, 05:50:09 pm
Use a BIG degree wheel if you want accuracy.   Note when the ports opens atdc and use math to figure the duration/closing.   In.other words don't use the degree wheel to physically check when the port closes.   Just when it opens
Title: Re: Port timing.
Post by: Cut4fun . on February 19, 2013, 06:15:04 pm
The 11" summit racing wheel at top of this link.   http://www.summitracing.com/search/part-type/degree-wheels     others there to choose from too.


Jegs racing 11" wheel  http://www.jegs.com/p/JEGS-Performance-Products/JEGS-Precision-Cam-Degree-Wheel/937108/10002/-1


Moroso has a 18" for twice the $$    http://www.summitracing.com/parts/mor-62191/overview/
Title: Re: Port timing.
Post by: jmester on February 19, 2013, 07:24:43 pm
I have a comp cans degree wheel.  Thanks for the info. Witch is a better read on porting Jennings or bell. I have read some of macdizzys stuff before.
Title: Re: Port timing.
Post by: Al Smith on February 19, 2013, 08:40:32 pm
You can down load Jennings if you want to .I'm not sure if you can Bell or not .

There's a lot of good stuff in both of them that I can't remember off the top of my head .They'll tell like how to figure time area open at certain perspective speeds and stuff like that .What good ports should look like and not so good of ports too and why they aren't so good .

What you have to watch is both of them as well as McDizzy get into motorcycle and snowmobile engines which have a larger crankcase volume  than a saw engine .If you just stick to the basics though won't have any problems .
Title: Re: Port timing.
Post by: 660magnum on February 19, 2013, 09:13:00 pm
http://www.filecrop.com/graham-bell-tuning.html

http://www.macdizzy.com/
Title: Re: Port timing.
Post by: Al Smith on February 20, 2013, 06:54:43 am
On that wheel deal they really aren't that hard to fabricate .McMaster -Carr sells the transfer which is heavy mylar resonabley priced in both left hand rotation or right hand  available in several diameters .

I've made several . You need to make an arbor to screw on the crankshaft whatever size that may be and I use sheet aluminum cut to the size of the wheel .I'd have to measure but if memory serves they are 8" .
Title: Re: Port timing.
Post by: jmester on February 20, 2013, 07:03:19 am
I have a degree wheel and an arbor/ hub to attach it. I was reading in bells book and he talks about filing some of the top of  the piston off , too give you some more exhaust duration. Is that practical in saw mods or mainly motor cross. Have you guys also found his exhaust and transfer duration charts to work with saws.
Title: Re: Port timing.
Post by: Al Smith on February 20, 2013, 07:10:54 am
That's one method some use .You either remove metal on the port or from the piston .I'm not so certain most chainsaw engine builders use that method though .
Title: Re: Port timing.
Post by: aclarke on February 20, 2013, 01:08:00 pm
The duration charts are really not the best suited for saw motors.  Piston speed on a square bore/stroke bike motor tuning 9500 rpm is going to be much higher than a saw motor with their over square (short stroke) motors. The time (duration) needed on a saw motor will be less until you start tuning very high rpm and need the extra time/area to support the higher Hp @ rpm.

Blowdown requirements on a bike motor might be 30+ degrees and many saws get away with half that.   Other factors weigh in but in general saws require less duration with their lower hp outputs & piston speed
Title: Re: Port timing.
Post by: Al Smith on February 20, 2013, 01:41:10 pm
Interesting subject .On the few I have taken the port time opening  measurements on ,both McCulloch and Stihl and one Poulan the exhausts were set anywhere from 96 to 101 after TDC and the transfers usually around 20 after stock regardless of who made the things .
Title: Re: Port timing.
Post by: jmester on February 20, 2013, 04:47:38 pm
Those reads have a lot of use full information in them. I do have one question can you change the transfer duration and leave the exhaust duration alone. I will have to study them for a while. I am thinking of raising the ex,trans back to stock height leave the intake alone and widen the ports. Any thing you guys would suggest, in regards to timing numbers. I think I might do what I mentioned above,see how it does.  And go back in if I want more or something different.
Title: Re: Port timing.
Post by: Al Smith on February 20, 2013, 06:38:13 pm
You lost me .Let me get this straight .You want to raise the upper transfers but leave the exhaust port low after you have lowered the cylinder ?
Title: Re: Port timing.
Post by: jmester on February 20, 2013, 07:21:27 pm
Yes, you are correct. I want to provide more fuel at mid range, I think I can do that you more transfer timing. I don't want move the exhaust, because I don't want to raise the peak rpm. May be I am lost with this stuff ? My exhaust is @102* and the transfers are @126*. I was thinking of raising the exhaust back to 101*  and raise the transfers to 120*.
Title: Re: Port timing.
Post by: 3000 FPS on February 20, 2013, 09:26:48 pm
I usually like a blow down of 20 and what your talking about is close.
Title: Re: Port timing.
Post by: jmester on February 21, 2013, 05:57:58 am
Also do you guys case match your lower transfers. I think I am going to raise those trans to 120* and see what happens. I did raise the exhaust last night. Went a little overboard. It came in at 99*. On older 0 model stihl saw is the cylinder coating Chrome. Because it was very soft. Should give me a blowdown of 22*.
Title: Re: Port timing.
Post by: aclarke on February 21, 2013, 03:53:21 pm
Port shap I.e round or flat plays a role on the way the motor runs as well as ring life.  You may try staggering the transfers vs. Having the top flat or if its a quad transfer motor open the intake side first then mains a few degrees later. As mentioned earlier by 300fps the shape and direction plays a big role, not just duration.   Some of the engine simulation software allows you to change transfer port angles, etc where you can see the different power characteristics generated by merely changing angles....
Title: Re: Port timing.
Post by: aclarke on February 21, 2013, 04:07:18 pm
if its a Mahle cylinder most likely Nikasil
Title: Re: Port timing.
Post by: jmester on February 21, 2013, 04:14:14 pm
I took the transfers up to 120. They are not staggered. I will think on that one that sound like a neat concept. I am working on putting back together. Will try to post a video when I get it finished up. To see what you guys think of it.
Title: Re: Port timing.
Post by: jmester on February 21, 2013, 04:22:47 pm
Would it be advisable to advance the ignition timing, or see where it is at first.
Title: Re: Port timing.
Post by: 660magnum on February 21, 2013, 04:56:46 pm
The more advance the timing is, the harder it is on your hand and arm when starting the chainsaw
Title: Re: Port timing.
Post by: jmester on February 21, 2013, 05:37:38 pm
Do you guys think that 130lbs of compression is too low for new rings. I had too clean the cylinder up ,the piston and rings were boogered up prettty good. Thanks for all the feedback and help.
Title: Re: Port timing.
Post by: 660magnum on February 21, 2013, 05:49:00 pm
You'll have to be the judge yourself. At 130 lbs it does need something done.

Rings don't cost much. Clean things up and throw in a set of rings and see what you got?

I bet it will last a while?
Title: Re: Port timing.
Post by: jmester on February 21, 2013, 05:56:33 pm
It is 130 with new rings, they should come up some as they seat in. I wonder if we will get 150 out of them.
Title: Re: Port timing.
Post by: 660magnum on February 21, 2013, 06:12:55 pm
It might come up to 140 but that will most likely be it.
Title: Re: Port timing.
Post by: Al Smith on February 21, 2013, 07:28:24 pm
If you've already cut the upper transfers you're pretty much stuck with them unless you drop the cylinder more .However if you would have left them alone you could have gotten a few more degrees of blowdown by raising the exhaust .99 won't hurt you though unless it won't come up above 130 PSI static . A new set of rings should jack it back up to 150 or so I'd guess .They're only about 5 bucks a pop for Cabers .

At 102 exhaust it would have pulled good but it wouldn't gain much if any on RPM .99 with good compression should if the blow down isn't out of sorts .That's just my theory which of course is up for debate .
Title: Re: Port timing.
Post by: 3000 FPS on February 21, 2013, 07:35:36 pm
What did the squish end up at when you measured it.
Title: Re: Port timing.
Post by: jmester on February 21, 2013, 08:04:37 pm
The squish came in at .025. I could have gone to .020. But I did not want to make it so tight. My blow down should be around 21*. I have 99* on the exhaust and 120 on the transfers.  Al, what do you consider to be good compression.  I should have it together tomorrow. I guess we will have to see.
Title: Re: Port timing.
Post by: 3000 FPS on February 21, 2013, 08:10:47 pm
I would think that with a squish of .25" that your compression should be at least 150psi or better.   Sounds like the rings are not sealing for some reason.   
Title: Re: Port timing.
Post by: jmester on February 21, 2013, 08:18:42 pm
Would it be because they are new.
Title: Re: Port timing.
Post by: 3000 FPS on February 21, 2013, 08:25:16 pm
Did you use any 2 cycle oil on the rings or cylinder walls when you assembled it.   
Title: Re: Port timing.
Post by: Al Smith on February 22, 2013, 05:17:51 am
150 would be good .Lowered cylinder it should be maybe 160 .I'm more inclined to shoot for 180 myself but I'm a little eccentric  just as I suspect those rings are . ;)

The way I look at a saw engine as far as  power curve is you basically have two ranges ,idle and wide open .Something like a bike or snowmobile engine a person might be concerned about mid range for an acceleration shot .On a saw I don't know too many people who run them half throttle .
Title: Re: Port timing.
Post by: Al Smith on February 22, 2013, 05:21:13 am
Would it be because they are new.
Well if that's the case put  that thing together and stick it in some wood and flog it like a borrowed mule .It'll either seat in or blow up which I doubt .
Title: Re: Port timing.
Post by: jmester on February 22, 2013, 06:05:37 am
Yes I did coat every thing with oil, pistin,rings, cylinder. May be when I was cleaning the bore up I got it a little out of round and that's why it is low. I used a flap wheel that was half shot. That's the plan, put it together and run it. 
Title: Re: Port timing.
Post by: Al Smith on February 22, 2013, 07:33:26 pm
May be when I was cleaning the bore up I got it a little out of round and that's why it is low. I used a flap wheel that was half shot.   
You didn't by any chance get deep enough to cut through the plating did you ?
Title: Re: Port timing.
Post by: jmester on February 22, 2013, 07:35:41 pm
No I looked at it after I was done. And could not see any spots.
Title: Re: Port timing.
Post by: jmester on February 22, 2013, 10:13:03 pm
I have the saw back together, hope to have some time tomorrow to make some cookies. Do you think with my timing numbers the max rpm changed if any.
Title: Re: Port timing.
Post by: jmester on February 23, 2013, 11:59:21 am
Ran a tank threw it. It runs pretty well, have not check comp yet. Turned 13,200 out of the wood. And about 9,500 to 10,200 in the wood . With 8t .325 pitch and 18" bar.
Title: Re: Port timing.
Post by: Al Smith on February 23, 2013, 05:23:15 pm
Well does it run better than before you fiddled with it ? If so ya done good .If not ya did  not so good .
Title: Re: Port timing.
Post by: jmester on February 23, 2013, 05:42:59 pm
I feel like it is stronger in the cut before.  I think I did ok. I guess time will tell. Is there and way to raise the in the cut rpms.
Title: Re: Port timing.
Post by: 660magnum on February 23, 2013, 08:49:27 pm
More horse power, lift up on the bar, or cut smaller wood.
Title: Re: Port timing.
Post by: 3000 FPS on February 23, 2013, 08:53:07 pm
Remember when we were talking about torque.   That is what gives you more rpm in the cut.
Title: Re: Port timing.
Post by: jmester on February 23, 2013, 09:05:38 pm
What is a good way to get some more torque. Any way to change my port numbers around to get some more out of it. Or should I just not expect so much from an 028.
Title: Re: Port timing.
Post by: 660magnum on February 23, 2013, 09:07:17 pm
lower the exhaust
Title: Re: Port timing.
Post by: 3000 FPS on February 23, 2013, 09:20:35 pm
I think I would try and find out why you only have a 130PSI for compression.   You are never going to get good torque out of that saw unless you bring the compression up to aleast 150PSI or more where it should be.  Or else just run it the way it is and see if it comes up some when you break it in.
Title: Re: Port timing.
Post by: Al Smith on February 24, 2013, 06:38:27 am
Well that 130 PSI static isn't helping things for sure .99 opening from 101-102 probabley has little if any effect .

In my way of thinking raising the upper transfers would not be benenficial because of two reasons ,First it would start the transfer at lower crankcase pressure and it conjuction with the exhaust opening there would not be the differentials of pressure existing between them.The transfer pressure phsically at the time of transfer has to be higher than the exiting exhaust pressure or else it just will not happen until it is so .

I wouldn't fiddle with it any more until you figure out why the static pressure is so low .Oh I suppose the intake side of the piston skirt could leak some crankcase pressure but it would really have to be concentric to do that .I mean out of round like a football .I've seen some really  funky pistons do a pretty good job

That flap wheel hone job probabley didn't help things but given enough run time the rings should wear in .Might take a while though .

Don't give up the ship just yet .FWIW the 038 Mag which a lot of folks on this forum have seen in action had a funky intake side from a torn boot .It took me nearly all summer cutting down from a 10 cord pile of oak to seat those rings with 5-10-15 minute run times .When those rings finally decided to straighten up and fly right it was like a jet with an after burner .

New rings on an old cylinder are  not the same thing as a complete new top end .It usually revives them but sometime it just takes longer .
Title: Re: Port timing.
Post by: jmester on February 24, 2013, 06:54:37 am
Ok, I will keep running it and try to seat those rings. I will keep you posted on what happens with it. This is my first time running a new piston and rings with an old cylinder. So it is a little different to me.
Title: Re: Port timing.
Post by: Al Smith on February 24, 2013, 07:33:27 am
I must have missed that part of a new piston just like I missed the part of new rings .Hmm.
Title: Re: Port timing.
Post by: jmester on February 24, 2013, 07:36:59 am
What do you mean by hmm. It is an oem piston kit.
Title: Re: Port timing.
Post by: Al Smith on February 24, 2013, 09:11:02 am
Hmm meaning I missed that part some how .I thought you just tweeked an already good running saw just to get a little more punch out of it rather than to repair what evidently was one with damage .I can't think of any other reason to replace a good piston.  So here is part of an earlier post ----It is 130 with new rings, they should come up some as they seat in. I wonder if we will get 150 out of them.----There wasn't even any mention of a new piston until two posts ago .
Title: Re: Port timing.
Post by: jmester on February 24, 2013, 12:02:29 pm
You are correct. I did take some measurements on the new piston and it matched the old piston well. The piston I took out of it had some deep scuff marks on the intake. I am thinking dirt or carbon got stuck. There was also some scuffing on the exhaust side as well. All marks where on the pto side of the piston. Would a new piston effect it that much. Will the heat cycles over time distort the cylinder.
Title: Re: Port timing.
Post by: Al Smith on February 24, 2013, 12:31:50 pm
Not likely .
Title: Re: Port timing.
Post by: jmester on February 24, 2013, 12:35:20 pm
I guess I will have to either run it or tear it down.
Title: Re: Port timing.
Post by: 660magnum on February 24, 2013, 12:46:56 pm
RUN IT!
Title: Re: Port timing.
Post by: jmester on February 24, 2013, 12:54:05 pm
That's what I will do. Thanks.