Only if you want to go down this road again.
Please Help Diagnose Piston Failure
- Thread starter Ramair08
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Chainsaw Jim
CJ Saws, LLC
That's a pretty big saw to be messing around with aftermarket. If it's a cheap throw away saw then I could see cutting corners being an effective solution. But this ain't no cheap saw.
Sorry for not updating sooner, work was very busy today.
The rings fit tight in the ring grooves, I checked the ring gap before I used them. I didn't really want to use aftermarket when I rebuilt it, but it was all I was able to find at the time though.
I think the failure is a combination of bad castings for the cylinder and poor quality material in the piston.
Interestingly though, this piston broke in the exact same place as the piston that only ran 10 minutes several years ago! (First photo)
The factory cylinder is shown in the second and third photos, the scratches don't seem as bad as they look. Do you guys think it is worth trying to clean up a little better or should I pull off the cylinder from my parts saw and see what that looks like?
The rings fit tight in the ring grooves, I checked the ring gap before I used them. I didn't really want to use aftermarket when I rebuilt it, but it was all I was able to find at the time though.
I think the failure is a combination of bad castings for the cylinder and poor quality material in the piston.
Interestingly though, this piston broke in the exact same place as the piston that only ran 10 minutes several years ago! (First photo)
The factory cylinder is shown in the second and third photos, the scratches don't seem as bad as they look. Do you guys think it is worth trying to clean up a little better or should I pull off the cylinder from my parts saw and see what that looks like?
Chainsaw Jim
CJ Saws, LLC
If any of those marks above the exhaust can be felt with your fingernail or tool it is toast.
Since this has happened twice to the same saw with both oem and aftermarket then maybe there are fragments of crank bearing passing cleanly through the transfers and catching on the way out to start the crack on the piston crown? I'm guessing you didn't build it originally with the oem parts that first failed? Or maybe something has been dropped into the carb twice while the filter was off?
Since this has happened twice to the same saw with both oem and aftermarket then maybe there are fragments of crank bearing passing cleanly through the transfers and catching on the way out to start the crack on the piston crown? I'm guessing you didn't build it originally with the oem parts that first failed? Or maybe something has been dropped into the carb twice while the filter was off?
Chainsaw Jim
CJ Saws, LLC
I'm not sure I'd want to rebuild that saw without pulling the case apart to give the bearings a full inspection, or actually just replace the crankshaft and bearings entirely.
drf255
BAD CAD
If the other piston also broke in the same cylinder, I'd worry about an as symmetric squish band in that cylinder, or just too tight a squish period.
A question for the pros here, do Pistons expand asymmetrically when they heat up? Is it possible that the hottest part of the piston, the exhaust side, expanded enough to pinch the squishband and the other parts didn't?
Good pickup Shawn. I thought it was a domed piston in the first pic.
I appreciate all your replies, I will try to answer some questions.
The original piston/cylinder was lean scored.
The second piston/cylinder (first aftermarket) ran 10 minutes before dramatic failure (shown in post 24).
The third piston/cylinder (also aftermarket, this was a replacement for the first aftermarket piston/ cylinder).
This saw has run a total of three pistons and three cylinders.
The AV Gas seems to leave a grey residue- from the lead I presume- on all the parts that come in contact with the exhaust, maybe this is why the piston doesn't have a normal carbon ring? I checked the squish with solder when I put it back together and seem to remember that is was on the wider end of what was acceptable on here.
The original piston/cylinder was lean scored.
The second piston/cylinder (first aftermarket) ran 10 minutes before dramatic failure (shown in post 24).
The third piston/cylinder (also aftermarket, this was a replacement for the first aftermarket piston/ cylinder).
This saw has run a total of three pistons and three cylinders.
The AV Gas seems to leave a grey residue- from the lead I presume- on all the parts that come in contact with the exhaust, maybe this is why the piston doesn't have a normal carbon ring? I checked the squish with solder when I put it back together and seem to remember that is was on the wider end of what was acceptable on here.
srcarr52
We can't stop here, this is bat country.
Yes, they do not expand symmetrically, but either does the cylinder. The cylinders actually get pretty out of round because of the way they are cooled. The hot area usually is the area farthest away from the flywheel (front right corner), which actually causes the cylinder wall clearance to get tighter in that area.
Also, judging from the aluminum transfer well over the none flywheel side transfer ports I'd say the piston to cylinder wall clearance was too tight or there was a cold seizing issue.
