parrisw
Tree Freak
Sorry I lied a little. The #'s are slightly different. Look here
http://www.arboristsite.com/chainsaw/168195.htm
http://www.arboristsite.com/chainsaw/168195.htm
re-building my 362/372 xp hybrid
- Thread starter benjy
- Start date
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srcarr52
We can't stop here, this is bat country.
I'm not a fan of the windows in a 372 anymore... I grind off the full skirt and then I don't have to push the transfer walls up so high to make it effective.
parrisw
Tree Freak
I personally don't see any negative effects of using a windowed piston in a 372, the one I just built I did not use a windowed piston, wanted to see the difference.
srcarr52
We can't stop here, this is bat country.
I think that you'll get more performance through cutting the full circle off then putting windows in. Because you get to keep more material in the crankcase so you keep the crank case compression and keeps the port velocity.
parrisw
Tree Freak
Not sure what you mean by cutting the full circle off?
I don't think adding windows effects case comp enough to even measure, its only changing the amount of material that was removed to make windows.
wigglesworth
Booned
Only real way to test is to do some timed cuts with the windowed saw, then swap in an non-window piston and do the same.
I "personally" like crankcase compression myself. Anything I can do to help that out, is ok with me.
wigglesworth
Booned
Making the flats on the side of the piston by the wrist pin go all the way down to the bottom. Cutting the lip off below it.
My thoughts....
By cutting the windows in it, you increase crankcase volume, and change the direction of the charge, even though it might be hard to measure. It does, however, lighten the piston and could help cooling the crown, so there might be gain in it.
parrisw
Tree Freak
Ahh, ok, I see what ya mean by cutting the full circle off. That's removing material as well too which effects case comp. I feel though its such a little amount of material that its negligible, however that's just my feeling which can mean nothing. My 372 with windowed piston runs really well, soo??? Who know. I don't think anyone has done any testing on it, once this new 372 I did get a little more run time on it, I'm going to do a head to head test, I know its not a fair comparison since it has way more compression then my older 372, and different numbers, but will be interesting none the less. I've often thought of milling down the case on a 372 and see how that effects things?? Thoughts?
srcarr52
We can't stop here, this is bat country.
Exactly what I'm thinking. I think by cutting the sides off you can get the flow increase without increasing the volume too much. As for cooling the piston, I'm unsure if that helps since the heat is going into the next up A/F mix which could be detrimental.
Lightening the piston is a good deal, especially if you grind a little off the crank at the same time. A single cylinder engine is around half balanced and there really isn't any reason to go much over that on a chainsaw with the way the AV systems are designed. Take the weight off and free up the power.
thanks guys, parris if mine runs as strong as your i'll be very happy! one of my friends has told me there is a guy near by me who tunes superbikes and motorcross for the top riders in the uk, hes a good friend of his and he said he will ask him to sort the machining stuff out, as i dont have the machinery for that. i shall keep you all up dated as it progresses....
parrisw
Tree Freak
Ya, good luck with it. Mine still puts a smile on my face every time I run it. Its been almost 2 years now ago that I put that one together.
got the cylinder and jug today, as someone pointed out earlier in the thread i need to get a round inlet (clamp style) instead of the bolt on. gave the exhaust a lick of primer, ready for black now! i was comparing the old and new jug and the transfer ports have no walls unlike my new one and the ones ive seen ported on here... the old one is totally open to the case, why is this? and which is better?
parrisw
Tree Freak
You're new one is better, closed port. In a nutshell, better flow.
Parris do you have a spare inlet manifold for my saw? can pay u via paypal if you are willing/able? having a hard time finding one here
parrisw
Tree Freak
Parris do you have a spare inlet manifold for my saw? can pay u via paypal if you are willing/able? having a hard time finding one here
Really!! Crazy, yes I do, in fact I think I have like 8 of them. PM me your address and I'll ship one out to you. I may or may not have a clamp, I'll check, and you'll need the mount for the carb end along with the little metal insert, unless your old one has that stuff.
Will
PM sent!
parrisw
Tree Freak
Ya, first use a degree wheel to get a base line, do your machine work, then check the #'s again and then go from there, then you'll know where to go, don't run any less then 20* blowdown.
srcarr52
We can't stop here, this is bat country.
I keep them right at 20.
