Piston/cylinder damage, what causes this? (Stihl MS260+250)

[MartDalb]

Hey everyone

Got myself some broken/dead saws from a local shop.

Anyhow, don't ask me how they got so dirty etc.

My question.
2 of the saws has the piston and cylinder broken, on the exhaust side, and only on the "top of it".
Take a look at these pictures.
The saws are MS260 and one MS250

How do you go about doing that sorta damage?

 

[Jasonrkba]

It ate something, maybe cerclip.

 

[grizz55chev]

Hey everyone

Got myself some broken/dead saws from a local shop.

Anyhow, don't ask me how they got so dirty etc.

My question.
2 of the saws has the piston and cylinder broken, on the exhaust side, and only on the "top of it".
Take a look at these pictures.
The saws are MS260 and one MS250

How do you go about doing that sorta damage?

Looks a lot like someone used something for a piston stop that they shouldn't have.

 

[82F100SWB]

Definitely foreign object damage. One looks like maybe a wrist pin clip.

 

[MartDalb]

It ate something, maybe cerclip.

Having not opened up the 251 (not a 250 sorry), the 260 has both clips in place.
The piston on the 260, only has minor scoring going down the piston as well.

 

[MartDalb]

Looks a lot like someone used something for a piston stop that they shouldn't have.

This I had not considered.
Both machines are from same "user" or "users". Landscape gardener company.
I don't have any inside knowledge about them, but I was pretty sure they did not work on their own machines, ever.
But it could surely explain this sorta thing, a damn shame too!

Would you think the cylinders could be reused with some work?
Or are they just dead and time for a full replacement?

 

[MartDalb]

Oh and the 260 will need alot of work, not sure if it is worth my time, or it will just end up as a spare part saw.
It is losing paint, and show signs of "magnesium rot". I has not been stored well.

The 251 is mostly just dirty, needs a clutch cover and some minor parts here and there.
It will be a shame if the cylinder needs replacement, the piston is dead though.

 

[grizz55chev]

Oh and the 260 will need alot of work, not sure if it is worth my time, or it will just end up as a spare part saw.
It is losing paint, and show signs of "magnesium rot". I has not been stored well.

The 251 is mostly just dirty, needs a clutch cover and some minor parts here and there.
It will be a shame if the cylinder needs replacement, the piston is dead though.

The cylinder might clean up, look for a meteor piston if it's available, they come with Caber rings and usually run around $40. Edit, looked it up,$37 delivered. I would stay away from all aftermarket pistons other than Meteor.

 

[MartDalb]

The cylinder might clean up, look for a meteor piston if it's available, they come with Caber rings and usually run around $40.

Yep, never use anything else than meteor for non OEM pistons.
Those markings in the cylinder though, I can grind em down, but I am not sure if they are too deep....

 

[grizz55chev]

Yep, never use anything else than meteor for non OEM pistons.
Those markings in the cylinder though, I can grind em down, but I am not sure if they are too deep....

It's worth a try!

 

[MartDalb]

Trying to take a better picture, not easy.

This is from the 251.
To me, this looks like the cylinder is too damaged to start grinding on.

Thoughts?

 

[smokey7]

Push a piston ring in the bore with a piston to keep is straight. Look at where it feels rough of catches. ID use a version of mastermind method to knock down any high spots remove any transfer put a new piston and rings and run it. Check for air leaks with those tiny seals on the flywheel side

 

[MartDalb]

So... Was tempted to run it.
So I did, and it runs fine.
Idles fine, revs fine.

Just use it till it dies?

 

[grizz55chev]

So... Was tempted to run it.
So I did, and it runs fine.
Idles fine, revs fine.

Just use it till it dies?

Run it like ya stole it!

 

[MartDalb]

Run it like ya stole it!

Damn strait I will!

 

[smokey7]

So I am assuming that you put it together with the original piston rings. Then only knocked down the high spots and you are running it??

 

[MartDalb]

So I am assuming that you put it together with the original piston rings. Then only knocked down the high spots and you are running it??

I didn't do anything at all....Cleaned out the carb and tested it.

Runs, and cuts....

When it stops working, ill just replace what needs fixing. Not sure when that is though.

(edit) This is the MS251, the MS260 has been torn apart and I am using fine grit to make it nice and smooth again.
Guess I should have mentioned that, the pictures taken from outside the cylinder+piston is the MS251. The others are all from the 260. Sorry