Ms460 hole in piston crown

[jk14]

This is a first for me, I'm no "pro" but I've been through my fair share of saws over the last few years, I've seen plenty of burned up top ends but never this.

I picked this saw up today brought it home, pulled the jug and found a hole in the piston. Cylinder looks decent no serious scoring or transfer, should clean up well. Just looking for any suggestions.

I plan on going through the saw and replacing all rubber components with OEM. , meteor piston and a carb kit as well. Followed by vac./press. test and muff. mod.

 

[Fruecrue]

Damn!
Wrong spark plug?

 

[jk14]

It had the correct plug in it when I tore it down but who knows what happened previously. I was kind of thinking along those lines. Maybe someone used a piston stop for clutch removal?

 

[Dub11]

Nitrous?

 

[67L36Driver]

Steel piston stop + impact wrench.

Happens quite frequently. [emoji849]

 

[nohoff]

Do you have some pics of the pin and the bearing?

 

[Fruecrue]

Steel piston stop + impact wrench.

Happens quite frequently. [emoji849]

Maybe you should find a better way.

 

[Terry Syd]

That looks like the hole was actually burned through the crown. There appears to be melted aluminum splattered on the inside of the piston. The front of the piston crown is also showing some pitting from heat. It appears to me to be from detonation.

Does the plug have bits of material adhered to it?

 

[jk14]

Yep sure looks like a piston stop deal to me. The best part is the kid I got it from said that they had a low compression issue before and it turned out to be a hole in the piston and they decided to replace the saw with an ms461... guess I'll be on the lookout for that 461 in a few years lol

 

[Terry Syd]

The last picture appears to have the piston in backwards.

 

[J_M____]

I have seen the flywheel key shear and rotate the flywheel just enough that it still keeps running but creates a ton of heat from the incorrect timing and can burn through like that if it happens in a long cut.

 

[Adirondackstihl]

I've seen water in the fuel do similar things

 

[jk14]

The last picture appears to have the piston in backwards.

Good call, I had set the piston back in the cylinder to see where it lined up, and had it in backwards. Here it is how it was upon disassmbly.

 

[jk14]

I have seen the flywheel key shear and rotate the flywheel just enough that it still keeps running but creates a ton of heat from the incorrect timing and can burn through like that if it happens in a long cut.

Good point, I'll have the flywheel off when I go through it to put the seals in. I think I might just split the case and do the crank bearings too.

 

[Terry Syd]

I wonder if the piston crown got damaged by a metal stop some time in the past. Perhaps using a 10mm bolt in the decomp? (I'm unfamiliar with the saw so I don't know if that is possible).

Once the crown got damaged, with a bit of raised metal to absorb heat and some hair line fractures in the crown, the piston became susceptible to a melt down.

Is that melted aluminum under the piston crown?

 

[67L36Driver]

Maybe you should find a better way.

Actually I’m for others using it. Makes a cheap rebuilder for me. [emoji108][emoji6]

 

[Bilge Rat]

Any splatter on the end of the rod?

 

[Chainsaw Jim]

It looks like the underside of the piston took a beating from the chunk that broke off.

 

[67L36Driver]

Almost as good, is a screwdriver poked in the exhaust port.

Guaranteed to pinch the rings and ding the cylinder wall.

 

[blsnelling]

Steel piston stop + impact wrench.

Happens quite frequently. [emoji849]

Exactly. They used the type of piston stop that screws into the spark plug hole.