Piston hit Plug

[Aggie2012]

Good morning gents

Hope you all had a good weekend.
Question for any one that has time to answer.

Got an MS 261 m Tronic that I’m rebuilding for a guy.

It was somewhat hard to turn over and after some disassembly found that the clutch drum bearing was missing causing it to be cock eyed.

Mild scoring of cylinder that cleaned up Nicly with my foredom, emery cloth, and scotch brite pad.

What I found odd was a nick taken out of the piston that looks like it hit the spark plug.

What would have caused this?

Sent from my iPhone using Tapatalk

 

[Lone Wolf]

Wrong plug was in at one time for a short time, crank bearings and or rod bearing severely worn or the mark is not from what you think and something else went in there.

 

[nohoff]

Is this an AM Piston?
The german MS 261 Pistons dont have this timestamps on top.

 

[p61 western]

Could be from a piston stop since it's obvious that the clutch was messed with.

 

[Iceboy]

Wrong plug???

 

[Iceboy]

Could be from a piston stop since it's obvious that the clutch was messed with.

That' a possible

 

[p61 western]

That' a possible

How does the rest of the piston look? Is it scored?

 

[Wilhelm]

Could be from a piston stop since it's obvious that the clutch was messed with.

I thought of this too.

Nice wash pattern.
Is that the desired wash pattern look?

 

[Aggie2012]

How does the rest of the piston look? Is it scored?

The rest of the piston looks pretty good for the most part.

Has some light scoring on the exhaust side but might be salvageable.

I’m thinking of finding a used piston on the bay with a fresh set of cabers just to be sure.

Do y’all think I should split it just in case?

Crank seems to roll freely now that I’ve got that clutch drum off. And I don’t find any slop.




Sent from my iPhone using Tapatalk

 

[p61 western]

The rest of the piston looks pretty good for the most part.

Has some light scoring on the exhaust side but might be salvageable.

I’m thinking of finding a used piston on the bay with a fresh set of cabers just to be sure.

Do y’all think I should split it just in case?

Crank seems to roll freely now that I’ve got that clutch drum off. And I don’t find any slop.




Sent from my iPhone using Tapatalk

You could probably just flush the crankcase with mix a few times, and then rebuild the top end. Just make sure there is no play up and down or in and out on the crank first.

 

[Lone Wolf]

The rest of the piston looks pretty good for the most part.

Has some light scoring on the exhaust side but might be salvageable.

I’m thinking of finding a used piston on the bay with a fresh set of cabers just to be sure.

Do y’all think I should split it just in case?

Crank seems to roll freely now that I’ve got that clutch drum off. And I don’t find any slop.




Sent from my iPhone using Tapatalk

Match up the mark on the piston to the plug by putting it in with grease on it to prove that was the cause, then it it safe to say it came from the wrong plug and no need to look elsewhere. If it dont match you need to find what came loose.

 

[Wonkydonkey]

One other thing, you say clutch drum bearing missing... Is it one of those cranks that have worn a bit to quick at the clutch bearing part.. worth a quick measure with calipers to see.

As for the piston mark. I'd guess it was some sort of piston stop but as nonoff says it's possible an am piston, any other pics of piston ?. If it is am,,, why, and do the marks match up on the p&c

 

[nohoff]

i mentioned this AM-piston as a possible sign someone messed with this saw before you

 

[wcorey]

Match up the mark on the piston to the plug by putting it in with grease on it to prove that was the cause, then it it safe to say it came from the wrong plug and no need to look elsewhere. If it dont match you need to find what came loose.

Pretty good chance some random piston stop would make a similar enough mark...

 

[Chainsaw Jim]

Electrode contact usually makes a nicer looking stamp mark than that. It looks an awful lot like someone either used a screwdriver or a piece of allthread rod with a rough edge for a piston stop.

 

[fearofpavement]

I concur with the "screwdriver piston stop" theory. Piston is probably fine as is, if it doesn't have anything else scary about it, just run it.

 

[Lone Wolf]

Pretty good chance some random piston stop would make a similar enough mark...

I never use them I us an impact gun they are plastic right will they do that?

 

[nohoff]

those plastic piston stops wont make trouble.
Steel piston stops make other half round marks.
Those marks are often on the exhaust half of the piston.
Look at the plug thread angle and the length of a standard piston stop

 

[Aggie2012]

I appreciate yalls feed back. I’ll check some of these things closer to the weekend and report back.

On a side note I myself have never used a piston stop. Always just snaked a rope off into that spark plug hole.

Any harm in that method?


Sent from my iPhone using Tapatalk

 

[p61 western]

I appreciate yalls feed back. I’ll check some of these things closer to the weekend and report back.

On a side note I myself have never used a piston stop. Always just snaked a rope off into that spark plug hole.

Any harm in that method?


Sent from my iPhone using Tapatalk

Others may chime in, but I have never had any trouble using the rope method. Also have had good luck with a cordless impact.