Chainsaw Repair
Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Modified Ported Work or Race saws => Topic started by: aclarke on February 04, 2014, 09:34:32 pm
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Anyone here ever play around with the porting on a 6400 jug? Have one here I'm gonna try on my 7900 just for kicks. Seems like a they should make real good power. looks like the 359 piston should work well, did a little port work, post some pics later Adam
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signs of flow reversal into transfers on this well used cylinder...
(http://i1184.photobucket.com/albums/z329/Aclarke123/DSC_0498_zps034ad1a5.jpg)
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Added a little time and area to the exhaust, hoping that allows For less of a delay in transfer flow...
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Where are you seeing the flow reversal on the transfers? Just wanting to know where to look and what to look for.
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dark exhaust deposits on the tops of the transfers ans the streaks on the the transfer tunnel
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streaks can be seen on the middle transfer in the pic
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more pics...
(http://i1184.photobucket.com/albums/z329/Aclarke123/DSC_0490_zps61257f22.jpg)
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intake...
(http://i1184.photobucket.com/albums/z329/Aclarke123/DSC_0487_zpsad797528.jpg)
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(http://i1184.photobucket.com/albums/z329/Aclarke123/DSC_0493_zps279c46c0.jpg)
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(http://i1184.photobucket.com/albums/z329/Aclarke123/DSC_0491_zpsf0b98dec.jpg)
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Interesting seeing the reversion. How much blow down is that cylinder running.
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Just guessing here but the piston on the right appears to be the 359, correct? Is the stock piston windowed?
I am interested in your performance results as I am replacing a windowed piston with a slab sided one in a closed port Husqvarna cylinder and I have a NOS 6400 saw I want to try some stuff on. Also, please post the measurements on both pistons, overall height, compression height pin center to top and pin top to top on the two pistons, if you would be so kind.
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Also looks that there may be another piston option from Meteor that has a 21mm compression height rather than the 20mm on the 359, it is windowed but full circle type rather that open skirt. Go here and have a look:
http://www.meteorpiston.com/Lists/Gardening/Join.aspx?List=831329fb%2Dc6b1%2D403e%2Dab58%2D966a2b8b6758&ID=1068&Source=http%3A%2F%2Fwww%2Emeteorpiston%2Ecom%2FLists%2FGardening%2FCatalog%2Easpx
Stihl model 08/TS-350 47mm may give a couple more possibilities, it appears to be slab sided but with a domed top. However it is taller by 6mm because of the domed top and has a compression height of 27mm, may be a very tight squeeze!
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Putting a new crank in the Saw. I'll Pat the before after number tonight.
The 359 piston seems to be within a mm both ways so it should be an easy fit
On this application I think a slab sided piston will work just as well. 359 piston is heavier, May remove a little weight. Adam
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So Adam, do you think that using a slab sided piston in a open port saw will better control the flow reversal you are seeing? Just wondering about your thought process behind the non-windowed piston.
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Perhaps, although the blowdown is likely the real issue. I put the New crank and bearings in the case and buttoned it up tonight so I'll be able to see what the original and altered timing number are.
I find it interesting that dolmar went to the slab piston in the 7900. Not that I don't think it works well but, however, the original piston was designed with asymmetric windows in the piston which were done for a reason and took a lot of thought and engineering. I'm very curious why they dropped that piston for the slab side?? Can the slab side be lighter? Hard to believe, but perhaps they opted for a lighter piston when the crank issues came up?
On a side note, the New crank I pressed into the bearings/crank halves had a lot more interference fit than any previous 7900 I've worked on. Almost Stihl tight!!! Lol
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So, is the new crank stroked or stock?
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I think the slab sided is lighter. I know Randy got more power with the slab sided with the same port timing. I'm thinking it keeps velocity up better for transfer flow.
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Slab pistons 5100 and 7900 are a lot lighter. Don't remember how much tho. I can get wt's on 7900 if needed. IIRC i wrote the wt on the box. I used windowed piston in my Solo 665/681 conversion because I went too wide on the ring end side. The windowed piston pin is in the middle. The slab pistons are in the box. I need to send em and have the pins relocated. I did measure skirt width the slab pistons are a little wider. Interesting the Solo 665 cylinder is quad port like the 7900 where the 6400 is open.
Shep
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Interesting. Wonder if the slab sided piston was a fix to reduce crank failures?
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I'm not sure why they changed to that. It seems to be a good change though.
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New crank is stock stroke.
Any ideas why the original 7900 had asymmetric (one smaller) windows in the piston? Seems like some thought went into that design, kinda odd they'd ditch it for the New piston unless it was a fix for something
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I can't remember when they come out. Cutting Scott would know a lot more.
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The only crank failures I heard about (from Dan Henry) were on the Solo 681. I haven't heard about 7900 failures. But taking an appreciable amt. of piston wt off can't be a bad thing. I had originally wanted to use the slab piston in the 665/681 for the lighter wt. knowing about the 681 crank failures.
Shep
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I was under the impression that slab sided pistons work better with open port transfers and windowed pistons worked best with closed port transfers. Interesting thread.
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Hard to say how this piston will work. Should be interesting
degree'd it this afternoon
stock:
Ex-106
trans-129
intake-143 (duration)
Ported:
Ex-101
trans-129
intake- 150 (duration)
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About new 7900 piston from 2011. Copy and pasted info below.
New "lightweight" piston for the 7900 for "better motor operation". Weighs 1/2 oz less than the original piston, 14.17grams lighter
It's still Mahle. According to the bulletin, "The light weight piston is required for a better motor operation."
Most dealers probably still have old stock in the 038130031 piston/cylinder kit. The new kit is 038130070, but you won't see it until the old inventory is cleared out.
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Thanks kev. Sheds some light...,
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I tried to buy the old OEM windowed P/C kit from Edge and Engine a year ago and was told by them that they could not get the old kits any longer. I could not get the Mahle windowed piston either!
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That's not a real long blow down. That seems pretty normal for a dolmar to make better power.
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Anyone remember the non-limited flywheel positioning at TDC? leading edge of magnet at leading edge coil @ tdc?? thk, Adam
(http://i1184.photobucket.com/albums/z329/Aclarke123/Mobile%20Uploads/DSC_0506_zpsa392df6a.jpg)
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It should be at the point where the poles of the magnet leave the armature of the coil?
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I've read about timing 2 different ways to do this. 1 was with a timing light and another with setting flywheel up like on the 3120 deal with 272 coil. I cant find the pic yet, but sent the timing light light way in PM.
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Thanks! Never tried the timing light method. I've used the method where the edge of the second coil pole is placed at the edge of the departing magnet (flywheel) at least that's what I remembered from 5-6 years ago. I degree'd the movement from where the flywheel magnet is centered on the coil poles and it moves 28 degrees til the magnet departs the edge of the coil. Would the point where the edge of the departing flywheel magnet be the point where the field collapses and spark occurs?
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http://www.foxvalleykart.com/timing2.html (http://www.foxvalleykart.com/timing2.html)
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Looks like good reading thanks.
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I read through the theory of how the ignition works. I have one question.
To turn on the darlington it uses one volt to forward bias it and allow current flow for the secondary.
So to turn off the darlington it uses another one volt. My question, is this a negative one volt to reverse bias the darlington and shutting it off?
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Picture
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Modification, construction, and timing of Husky 272 coil winding into a 7900 coil armature frame
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much appreciated!! makes it easy...thanks
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3000, i dont get that part of the Darlington coil either< gonna study it more
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Ok I was looking at the diagram for the magnetic field shown in the explanation and it shows the current reversing direction thru the trigger coil thus producing a negative voltage instead of a positive voltage. That would then reverse bias the darlington and turn it off and collapse the field in the primary and inducing a voltage into the secondary. Spark away.
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+1
There's a pretty good explanation of both a points system as well as a SIM and a more simple electronic ignition system in one of the Stihl service manuals
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Ok, Transistors take the place of the points. Solid state...
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I did not realize there were so many different designs to do the same thing.
The first one uses a darling transistor with a trigger coil to control the spark.
The second one uses two transistors along with a Zener diode to control the spark.
The third one uses a SCR, they call it a thyristor and a trigger coil to controll the spark.
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I searched till I gave up. Nice find Jim WTG and Thank You. 8)
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Yep, searched for hours to no avail!!!
Any idea on what trigger type a standard coil uses? Adam
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I have no idea myself.
The first one which was a Briggs magnetron looked like it was one piece with trigger and coil all being one part.
The second one which was a Bosch was two piece one being the trigger circuit and the other the coil.
The third was a Sem and was all one piece where the trigger and coil is all one part.
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EHP says he just slots the mounting holes on 272 coil instead of swapping the cores.
Shep
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The Stihl SEM coils are advancing coils if anyone is interested in such technology?
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Be interesting in seeing how the stihl circuit works..
,Shep, It's got a 272 type coil in it now, Saw was set up years ago on alky/pipe where the unlimited coil worked great. I don't think it makes any difference gonna work Saw, but the only flywheels I have have the key machined out. Need to order a couple small part to finish things.
stole an HD12 off a Husky, need to figure out a better choke lever for the Dolmar choke rod
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Ran a tank through the Saw today in 18-20" wood and was pleased with the torque. Used the coil timing method in the picture and added about 3 degrees more advance. Didn't seem to turn up very high, but pulled the lgx through some very hard eucalyptus nicely.
I'll take a vid later this week, maybe use a 440 or 460 for comparison as I don't have another dolmar
Adam
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Sounds like it's running strong Adam.
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Might monkey with the timing a little, see if it will pick up a little rpm
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460 in some hard dry eucalyptus 14"
http://s1184.photobucket.com/user/Aclarke123/media/Mobile%20Uploads/017_zps6bbf68d1.mp4.html (http://s1184.photobucket.com/user/Aclarke123/media/Mobile%20Uploads/017_zps6bbf68d1.mp4.html)
(http://i1184.photobucket.com/albums/z329/Aclarke123/Mobile%20Uploads/th_017_zps6bbf68d1.jpg) (http://i1184.photobucket.com/albums/z329/Aclarke123/Mobile%20Uploads/017_zps6bbf68d1.mp4)
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6400 in the same log, both 8 pin, but chain, bar variable, etc. pulls good for a 65cc motor, 460 would likely be faster with same bar/chain
http://s1184.photobucket.com/user/Aclarke123/media/Mobile%20Uploads/dolmar6400_zpsb777dacc.mp4.html (http://s1184.photobucket.com/user/Aclarke123/media/Mobile%20Uploads/dolmar6400_zpsb777dacc.mp4.html)
(http://i1184.photobucket.com/albums/z329/Aclarke123/Mobile%20Uploads/th_dolmar6400_zpsb777dacc.jpg) (http://i1184.photobucket.com/albums/z329/Aclarke123/Mobile%20Uploads/dolmar6400_zpsb777dacc.mp4)
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Adam, that 6400 runs very well! Even sounds like it is a torque machine! That is the 6 transfer version, is it not?
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Tim. Saw has great torque, doesn't seem to rev real high but that's ok. I'll put a tach sometime, six open ports. Has the 359 piston with the intake and exhaust widened a bit. More BD too
chain is new lgx filed once, really nasty hard piece of wood as you can tell.
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Nice Bobcat :)
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The 460 sounded like it was straining a lot more than the Dolmar. Pretty cool saw you built Adam.
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I'll make another vid with the same chain. Curious to see how close the Dolmar is to the stihl
Adam, just a "baby" Bobcat!! Lol works great for backyard tree removals. Non turbo so it's a little sluggish at Times.
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I'll make another vid with the same chain. Curious to see how close the Dolmar is to the stihl
Adam, just a "baby" Bobcat!! Lol works great for backyard tree removals. Non turbo so it's a little sluggish at Times.
I bet we could add a turbo or two on it... ;)
Whatcha gonna use the 6400 for?
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The 460 sounded like it was straining a lot more than the Dolmar. Pretty cool saw you built Adam.
Didn't want to throw rocks but I noticed the same thing as Roger did. RPMs make da noise, torque do da work!
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Think the 460 is a little lean on the top end and chains weren't equal imo. I'd like to run a few tanks through the Dolmar to see if there is any carbon in the transfers like before the addition time area was added to the exhaust
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I'm curious if anyone has tried using a small primer bulb in lieu of a choke butterfly? Thinking of removing the choke shaft and installing a small nozzle to spray a shot of fuel into the venture. What would the drawbacks be?
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Adam I remember a hotter woods ported 026 that ran the primer bulb set up (even though choke set up was different then your talking, the choke was still bypassed). I ran the saw at gtg's a few times and primer set up worked good.
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Thanks Kevin. Was curious about this, do away with the choke shaft and shutter, might make a small improvement in airflow.
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I'm curious if anyone has tried using a small primer bulb in lieu of a choke butterfly? Thinking of removing the choke shaft and installing a small nozzle to spray a shot of fuel into the venture. What would the drawbacks be?
I have worked on a few 2 stroke ice augers that do that.
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The predecessor to the 6400 Dolmar pretty much did exactly that. The Dolmar "i" models all had a Tillotson carbs with a squirter right off the carb pump when you turned the carb choke lever on. None of these had an actual choke.
Saws like the 6000i, 6800i, 111i, & 115i would all do this. In cold weather these saws will start and continue to run with the choke lever on. Turn the choke off as the saws have run a few seconds.
These saws are no longer in production.
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The predecessor to the 6400 Dolmar pretty much did exactly that. The Dolmar "i" models all had a Tillotson carbs with a squirter right off the carb pump when you turned the carb choke lever on. None of these had an actual choke.
Saws like the 6000i, 6800i, 111i, & 115i would all do this. In cold weather these saws will start and continue to run with the choke lever on. Turn the choke off as the saws have run a few seconds.
These saws are no longer in production.
Yup I have a 120Si like that, easiest starting saw ever built.
Maybe find one of those carbs Adam and see if you can put it on the 6400?
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That would be cool. I'll research it. Thanks
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Looks like HS236D. So there was a primer bulb on the saw somewhere??
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The predecessor to the 6400 Dolmar pretty much did exactly that. The Dolmar "i" models all had a Tillotson carbs with a squirter right off the carb pump when you turned the carb choke lever on. None of these had an actual choke.
Saws like the 6000i, 6800i, 111i, & 115i would all do this. In cold weather these saws will start and continue to run with the choke lever on. Turn the choke off as the saws have run a few seconds.
These saws are no longer in production.
Yup I have a 120Si like that, easiest starting saw ever built.
Maybe find one of those carbs Adam and see if you can put it on the 6400?
The 120Si and 6800Si were pretty much identical except the brake on the 6800 would trip off inertia. (was a EPA thing?)
That was the end of the Sachs era as the 6400 and 5100 were initially designed by Solo long after Dolmar was bought by Makita.
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Good one Adam did on porting a Dolmar 6400