Piston Question

[otisdog]

I've got a MS 361 that has a recently replaced OEM piston and cylinder that has 2 to 3 hours on it. I pulled the muffler so I can open it up a bit, and found what I (a chainsaw novice) thought was premature wear to the right of center on the piston. Is this normal? The shop that replaced the P&C did it on their dime because they straight gassed it while it was in for service. 93 octane non ethanol with stihl oil @ 50:1.
Thanks

 

[ElevatorGuy]

Looks like they missed something on the rebuild.

 

[otisdog]

Another pic

 

[ballisticdoughnut]

Your certain they replaced the cylinder? Have you made any carb adjustments? Could be a touch lean on the high speed. Also cutting with a dull chain can cause scoring due to over heating.

 

[ammoaddict]

Your certain they replaced the cylinder? Have you made any carb adjustments? Could be a touch lean on the high speed. Also cutting with a dull chain can cause scoring due to over heating.

Doesn't look like it does it.

 

[Mad Professor]

That looks like damage from debris from sloppy cleanup before assembly to me. Lean scores are going to start on clutch side.

I have a 036 from the 1990s never been apart still has the machine marks and no gouges like that.

 

[ballisticdoughnut]

Doesn't look like it does it.

Looking at the pictures again, the cylinder does look pretty clean. That doesn’t necessarily mean anything either way. They could have just cleaned the original cylinder up (if they caught it in time) and replaced the piston and rings. Seems like a shop would want to fix it as cheaply as possible if it’s on their dime. Of course this is all speculation based on the evidence at hand.

 

[ballisticdoughnut]

That looks like damage from debris from sloppy cleanup before assembly to me. Lean scores are going to start on clutch side.

I have a 036 from the 1990s never been apart still has the machine marks and no gouges like that.

Good point. That could very well be the case.

 

[bwalker]

Looks like the start of a lean seize to me.

 

[bwalker]

Good point. That could very well be the case.

Debris damage doesn't typically look like that.

 

[ZeroJunk]

No, it's not normal. Piston is starting to melt. Too lean or not enough oil mixed, take your pick.

 

[huskihl]

I don’t think they cleaned up the straight gassed cylinder well enough.

 

[Mad Professor]

Looks like the start of a lean seize to me.

That starts on clutch side where cyl/piston is hottest.

I think the mech was sloppy and something fell in crankcase during rebuild.

 

[Yukon Stihl]

Talk to the shop
If they wash their hands of it then it's time to pull the jug.
If you have the tools vac and pressure test before taking it apart.
You could adjust the squish while you have it apart,compliment the work you were going to do on the muffler

 

[huskihl]

I don’t think they cleaned up the straight gassed cylinder well enough.

Or the rings they used were too tight to the bore

 

[bwalker]

That starts on clutch side where cyl/piston is hottest.

I think the mech was sloppy and something fell in crankcase during rebuild.

Sometimes it does, sometimes it doesn't.
Debris damage doesnt rub one small area. You find it all over the place and randomly.

 

[farmguywithasaw]

Ring end gap was probably too tight in my opinion

 

[bwalker]

Ring end gap was probably too tight in my opinion

Very unlikely with a chainsaw, although it does sort of look like that.

 

[stihltech]

On this age of saw, a pressure/vacuum test is mandatory. I replace the carburetor also. You have a very light lean seize. Dirt from reassembly will not do this. Start looking for a lean condition from the fuel up.

 

[cookies]

damaged piston from heat expansion, the remaining ridges on the skirt appear to be wearing down as well. I can see the damage also forming beyond the right side of the window s well.
Try your hand at warranty again or snatch that cylinder off and install another piston yourself. Either way the H needle needs adjustment and luckily there is a lot info in here on how to do it.