MS440 piston/cylinder (pic heavy sorry)

[altair]

Okay stripped it down before, due to the marking on the edge of the piston.

Obvious to me something has been floating round in there?

Original Stihl cylinder, have photos of numbers attached.

No up and down movement in crank, some sideways, (normal?) but has movement in the piston/wristpin area. Circlips attached still.

Minor marks in cyl, nothing I can feel with fingernails

Don't know if this is Stihl piston or not, rings are free.

Does anything here look like a failing seal or air leak? Saw was running 100% as always but I thought I heard a rattle for a few seconds.

Appreciate your knowledge guys, I'll get Stihl shop to check crank before I purchase anything.

 

[altair]

Any chance it could be the piston itself just starting to fail?
Any way to identify if that piston is Stihl, or aftermarket? I'm betting aftermarket.

 

[mkinslow]

Any chance it could be the piston itself just starting to fail?
Any way to identify if that piston is Stihl, or aftermarket? I'm betting aftermarket.

No. Something was definitely inside there. Did you check your muffler to see if it was still inside. Shaving leftover from a muffler mod???

 

[Pioneer]

Bizarre, it looks like it ingested fine gravel and pounded it in the squish area. Is that chrome plating coming off of the cylinder, or is it just dirt or a reflection?

 

[mkinslow]

I'd bet it's something kinda soft material wise. I say that because the rings are still loose. When I tore down an 066 with damage from a bear cage failing it was beat up pretty bad but it also hit along the edges like that on exhaust side and deformed it enough the top ring was stuck.

 

[Derrick Sawyer]

Looks like some was grinding on the piston transfer windows and if it wasn't done evenly, could lead to more vibs and premature failure of wrist pin bears, which it looks like it lost a needle bearing or two that was pushed up the port to above the piston, bypassing the rings. Even if piston was stock, which you could tell by cleaning and lightly sanding the top-stihl oem should have an AB and small arrow, aftermarket just has a larger arrow, or oem say Mahle on the underside of the piston near the bearing. With the piston off, i fill the bottom end with WD40 or transfluid, spin the crank many times, hold upside down to drip out onto a pan, then stuff some papertowel in there and rotate crank all the way around again, and see what you get...i repeat till i cant see anymore gray shaving, and then you can see if the crank bottom end is ok.

Also the wrist pin clips, in one pic i can see one end but not the other, the gap shouldn't be that big and prefer to have the gap more vertical so the end is past the notch there.

 

[altair]

Took it to the Stihl guy today who studied it for a bit and decided it was probably a bearing starting to let go. He wasn't 100% sure on that, but looking at the piston/rings etc said it was plain ol "wore out". Funnily enough didn't try to sell me a new one either.
I won't spend money on it, I have the 661 which can use the 440s bars and chains. ..this oil girl can go on an auction site here for $1 reserve.
Appreciate your ideas and knowledge guys, thank you.

 

[cedarshark]

Unless that saw is really trashed...its certainly worth the repair.

 

[blsnelling]

That's definitely damage from a foreign object, not detonation as I thought.

 

[cedarshark]

I have had a small ball from a decomp button do damage that looked very similar. I just could not figure out how it dropped onto the top of the piston.