Chainsaw Repair
Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Husqvarna => Topic started by: KilliansRedLeo on May 12, 2014, 09:30:06 am
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Putting a 272XP piston in an AM BB kit for a 372. Well the piston is too tall for the jug even with 3 gaskets. I don't have the equipment to cut the squish or do a pop up piston. Was wondering if anyone here could do either job for me and what I would need to send out to get it done and the cost/time involved. Want to run no base gasket.
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Why not use the stihl 064 piston?
Easier and more skirt width for porting.
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I build those all the time. No challenge in that. They do run well when done and a lot less work. I'm after increased compression and a change in intake timing by using a taller CH height of the 272 piston and a 3-4° change in intake timing by using a 272XP piston which is shorter in OH.
Just an experiment, others have tried to do it with hit or miss results, so was bored an needed something to play with, instead of repairing customer saws all day. May be a total waste of time in the end.
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Well, it looks like I will have to put a pop-up on the 272XP piston to get this to work. With three 0.020 base gaskets I only get 0.0112 squish. Adding a fourth gasket would get me to 0.03112.... too much and four gaskets would be around 0.080; if 1° timing change is 0.018-0.019 I would be changing the timing by 3-4° that's not so good either, on top of that the piston being shorter overall would equal a BIG timing change.
Decided that popping up the piston is the best route because the experiment may be a bust, I would rather ruin a $30 piston than the jug. This way if the experiment fails I can always put the BB kit piston in the saw, delete the base gasket and have a decent runner.
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I do machine work for people all the time. I usually charge $40 to cut squish and base of a cylinder. If you just want a pop-up cut I'll just charge you $15. I can also cut some off the whole piston crown if you don't want the 0.07" pop-up required to get it to fit.
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That is not a bad price on cutting the squish and base on a cylinder. I will have to keep you in mind.
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Well, it looks like I will have to put a pop-up on the 272XP piston to get this to work. With three 0.020 base gaskets I only get 0.0112 squish. Adding a fourth gasket would get me to 0.03112.... too much and four gaskets would be around 0.080; if 1° timing change is 0.018-0.019 I would be changing the timing by 3-4° that's not so good either, on top of that the piston being shorter overall would equal a BIG timing change.
Decided that popping up the piston is the best route because the experiment may be a bust, I would rather ruin a $30 piston than the jug. This way if the experiment fails I can always put the BB kit piston in the saw, delete the base gasket and have a decent runner.
Nothing ventured, nothing gained. Lets regroup on a tweak on the 064 build concept!
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Well I used a different set of cases and all is well. 0.024 squish no machining.
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Had the case and top end all buttoned up, ready for pressure/vac testing. Saw failed the test, huge leak on clutch side of case, changed the seal used 1194 on the seal to case joint and changed the o-ring, no luck. Pulled the saw back apart and found a hairline crack in the case at the bottom of one of the webs surrounding the bearing cup. So tore the thing apart and Chainsawr saved the day with another case half.
Will start the build over again when the case half arrives in the mail.