cuinrearview
Red saw lover
Sand with 300-400 grit until all the carbon and aluminum transfer is gone. Finish with scotch brite pad.
Which Piston would you use? (Stihl 026 Pro)
- Thread starter davefr
- Start date
Help Support Arborist Forum:
Cylinder looks real good now. I'd still go with an OEM or Meteor piston. If you buy a stihl gasket set it comes with seals, and cheaper than seals alone.. You need gaskets for cyl and ex anyway.......... And the seals are known weak spot on the 026, flywheel side if I remember?
the saw was not straight gassed in my opinion, it has a vacuum leak, those seals are old check them good, I would replace them
Some of you guys tell every saw builder to put in new seals. I wish I could check your driveways. Probably oil leaking down from leaking seals for months. Your wife's car has a dirty air filter and the oil change is 3,000 miles past due but your saw has new seals!
If you read my post you would see why I think they need to be replaced!
cuinrearview
Red saw lover
I've been thinking more about this lately myself Mike(not the leaking oil in the driveway) and wrestling another FW side small Stihl seal out really brought it to the surface. I think because they're cheap and fairly easy to replace people always recommend them. It makes sense to a degree, cheap insurance. But we'll never hear about another leak found later, straight gas, etc, that turned out to be the cause later.
I read your post. I've read lots of your posts. You parrot other guys "squawk; change the seals, change the seals"
You can check all the rubber besides the seals when you do a P/C job, assuming you have a look at carb/fuel line also.
Seals are an unknown unless you vac/pres test.
So it seems a decent saw here and with a quality piston it should run nearly new. But the seals are ~25 years old.
A base gasket and ex gasket are going to be ~$6, a gasket set w/seals ~$17. So $11 more, and the saw is clean and apart NOW.
Why cheap out?
drf255
BAD CAD
Is your cylinder a 44 or 44.7 bore?
If it’s 44.7, oem pistons are available for around $25. There was a surplus, they are drying up.
If you don’t have a caliper, show me the outside of the cylinder, the sides and the top.
Look inside the AM piston skirts. Do u see any letters cast in? If it came with Cabers, it could have “mp” cast in and indeed be a meteor.
Like CIRV is saying, you need to diagnose why it failed. Look at the Fly side seal, usually the culprit.
BTW, your cylinder cleanup looks fantastic.
If it’s 44.7, oem pistons are available for around $25. There was a surplus, they are drying up.
If you don’t have a caliper, show me the outside of the cylinder, the sides and the top.
Look inside the AM piston skirts. Do u see any letters cast in? If it came with Cabers, it could have “mp” cast in and indeed be a meteor.
Like CIRV is saying, you need to diagnose why it failed. Look at the Fly side seal, usually the culprit.
BTW, your cylinder cleanup looks fantastic.
davefr
Addicted to ArboristSite
The bore is 44.7. What's the source of the $25 OEM pistons. I didn't see them on Ebay?
I do plan to test the bottom end for leaks but this saw sure doesn't look like it's had much use for seals to wear out.
I wonder if the saw was run in an over rev'd condition for an extending time? Like from a very dull chain and/or a overly lean carb adjustment? Most of the dust I see has been pretty fine dust vs chips. Would an extended over rev condition cause so much wear on the piston skirt?
I'm also wondering is there was a manufacturing flaw in the OEM piston. There's absolutely no visual signs of the skirt wear. It looks like it was manufactured that way.
TIA
I do plan to test the bottom end for leaks but this saw sure doesn't look like it's had much use for seals to wear out.
I wonder if the saw was run in an over rev'd condition for an extending time? Like from a very dull chain and/or a overly lean carb adjustment? Most of the dust I see has been pretty fine dust vs chips. Would an extended over rev condition cause so much wear on the piston skirt?
I'm also wondering is there was a manufacturing flaw in the OEM piston. There's absolutely no visual signs of the skirt wear. It looks like it was manufactured that way.
TIA
yup, that is one of the first things I do is a leak down test when I get a saw in and last things after the rebuild, must be a reason for a scored piston plus use my own gas mixture before starting it up, takes a lot of guesswork out of it.
drf255
BAD CAD
It appears the supply has dried up. I literally purchased 10 of them in the last 2 years for anywhere from $13-20 shipped, no pin and one circlip.
If you look at new OEM piston you will see machine marks running around the skirt (see your AM piston). First sign of wear is these are gone. I have several older stihls with lots of time on them and through ex port the marks are still visible. That's why pull the muffler and have a look before tearing down or buying a used saw. Machine marks there, piston is A O.K.
Your piston is badly worn, and/or as mentioned a prior attempt to remove scoring with sandpaper.
Look over post #30. You might have a Meteor piston (casting mark), and flywheel side seal is a weak point. The $25 OEM pistons were on Ebay but they are NLA.
Couldn't agree more. My point was not "change the seals" but rather, do a P&V test on all saws. It's like Forrest Gump's box o' chocolates, only sometimes you find a chocolate covered t*rd.
I wouldn't buy a new piston for this saw, especially if I already had one. If the new AM piston measures okay go ahead and try it. I would change the circlips and the rings though..
You'd put the used one back in with 0.0145" clearance, if you didn't have another?
Maybe?, the new one is from one of those $25 p/c kits? You'd run that?
Seems that saw is in decent shape and deserves a quality piston.
I thought the OP already had a new piston for the saw. No, I wouldn't put the old piston in the saw. I've had pretty good luck running aftermarket pistons but maybe that's all it is, luck. I don't run anything super lean however. I would measure the piston first as I stated.
Point taken but Chi-Com pistons can be little better than beer cans. If the piston he has is quality , use it. I'd measure everyplace and compare to OEM first before I took a chance.
There are threads here about fitment issues, low compression due to huge squish, circlips popping out, skirts hitting cases...... It looks like clearance is reasonable from posts. The rest???
I don't think the brand of his new piston was mentioned unless I missed it. I'm sure some aftermarket parts are better than others.
