new cylinder & piston questions for 45mm stihl 029

[r7000]

Rebuilding an older Stihl 029, unknown hours, friends saw I used it 5 minutes idled great, shut off never restarted, starting fluid would get a 1/2 second kick at best, and could hear rubber squeak pfft when pulling cord so i assume crank seals or pan seal let go.
The saw is/was in excellent condition, ignition coil tests fine, pretty sure carb is good non-ethanol gas used for a long time and engine ran perfect just never restarted. Doing a compression test i could get it up to 140-150 psi max, would hit 70-90 psi on one pull of the cord.

I have everything apart and new seals on the way, but since this far in looking for advice if I should do a new cylinder and/or piston kit? If so, can I reuse the existing crank pan?

The existing piston diameter, above the top ring measures 44.78mm. Measuring the ring outside diam compressing with my calipers i can get it down to 45mm. So how can i best tell if the saw was a 45mm 029, or a 46mm 029? And I kinda want to just do a new cylinder and just rings reuse existing piston everything looks fine, is that good/bad/not advisable?

If i go a big bore kit I assume the 49mm one is the largest and the one to go with? In any case if going larger than my existing since we are talking < 5mm difference can the existing crank pan be reused (looks hard to remove from saw shell) and

if I do a larger piston + cylinder on existing crank assembly does new piston weight matter, will there be an imbalance at 10k rpms, is that something that needs to be accounted for when retrofitting? I do have a good gram scale and i am not new to balancing stuff like this.

 

[Dub11]

Welcome and yes you can reuse the crank and crank pan. And 029=45mm piston and 029 super 290 is the 46mm piston.

There is a popup piston available for the 49mm head of you go that route and you can gain some compression.

 

[Dub11]

What's the cylinder look like? Usually you can clean it and get a new piston and rings.

 

[r7000]

so getting a pic of inside of cylinder is tough, the detail washes out so a pic is about useless but i'll try again later.
it is quite clean, normal light carbon buildup at top around spark plug hole, what carbon residue in the exhaust port pretty much wiped out with a rag and lacquer thinner.
No score marks.
I can see cross hatching at the very bottom near crank side where the piston rings do not ride, but further in it looks polished I don't know what to expect to see other than I don't want to see discoloration, melting, aluminum transfer.... had 2 saws years ago wrecked on me and when i pulled them apart one did not need any kind of diploma to know what was bad. This is my first tear down of a working saw known to be in good condition no obvious problem.

what worries me is going a new 49mm piston and cylinder kit and reusing existing crank assembly - how does one account for balancing?
I can weigh the original piston and pin and then the new 49mm piston+pin+rings and make a judgement, but i wonder if there's a balance problem now which led to existing seal problem? And not so sure i buy into the guarantee or hype of just throw on a larger piston it'll fit and work... yeah for a little bit.

Does anyone do anything about rotating & reciprocating balance when retrofitting a lager (49mm 039) piston onto the rotating crank/rod assembly from an 029 that used a 45mm piston? I'm all for spending an extra $50-100 at this point if it gets me a new motor and more power but not if it lasts only a few hours.

 

[Dub11]

It's the same crank for all the saws nothing to really worry about there.

 

[huskihl]

Same crank in all models from 029-039.

 

[Lightning Performance]

Al Smith will chime in to help you out and answer all your questions.
@Al Smith

 

[r7000]

Same crank in all models from 029-039.

so you guys just buy new pistons, either same size at 45mm or bigger at 49mm within that range and just throw them in?

anyone ever weigh pistons: an oem (stihl/mahle) piston and compare it to whatever quality aftermarket pistons are that are being sold?

 

[huskihl]

so you guys just buy new pistons, either same size at 45mm or bigger at 49mm within that range and just throw them in?

anyone ever weigh pistons: an oem (stihl/mahle) piston and compare it to whatever quality aftermarket pistons are that are being sold?

Yep that's what we do
Meteor is usually a few grams heavier than
Oem. But not enough to make a difference

 

[Lightning Performance]

Yep that's what we do
Meteor is usually a few grams heavier than
Oem. But not enough to make a difference

A few grams is few grams!

 

[huskihl]

A few grams is few grams!

You can use the lighter piston in the 029, I'll take the 10 extra cc's every time

 

[RocketRoss57]

You can use the lighter piston in the 029, I'll take the 10 extra cc's every time

Troof! I've done a few of these and it's a night and day difference coupled with a muff mod. And got ALOT of run time out of them with no problems other than NOT using the aftermarket wrist pin clips!