Damaged pistons and barrels

[gagvanman]

Stripped my 1776 down after had the flywheel come loose the other weekend. Camshaft is ok, crank is ok but still need to check journals for any sign of ovality. However; got this strange damage to the top edge of 3 of the pistons (funnily enough not piston 3).
Anyone any idea of what might have caused this?
Going to replace all the bearings and flywheel, now I suspect I need new B&P’s…

 

[sparkywig]

Looks like detonation to me

 

[K@rlos]

Looks like detonation to me

I agree, engines been run with too much timing or been really lean

 

[ozziedog]

Ozziedog,,,,,,,,show us the barrels bud.

 

[james_stan]

Those markes appear to coincide with the ring gap - could that top ring be gapped incorrectly.

Random guess obvs.

 

[matty74]

Sorry to hear and see, I remember you having engine overheating issues and fuel in sump etc a while back, do you think it may have started then?

 

[sparkywig]

Those markes appear to coincide with the ring gap - could that top ring be gapped incorrectly.

Random guess obvs.

Piston rings rotate circumferentially, not stay in one place.

 

[67panel]

Looks like overheating (for what ever reason) but need to see barrels to be sure.

 

[james_stan]

Piston rings rotate circumferentially, not stay in one place.

Ah right, thought I could make out a locating 'peg'. long time since I did the top end on one.. different on two strokes where you have to prevent ends snagging on ports.
As you were..

 

[ozziedog]

Looks like overheating (for what ever reason) but need to see barrels to be sure.

Zackerly what I said.

Ozziedog,,,,,,,,show us the barrels bud.

Going back to the fuel in oil scenario, that ain’t gonna help matters anywhere.

Piston rings rotate circumferentially, not stay in one place.

Might be worth looking at the gap anyway while it’s apart. Maybe they and I say maybe they couldn’t rotate if they weren’t gapped enough. Funny how it’s happened on three out of four. Might look at any tiny differences between those three and the odd one.

Ozziedog,,,,,,,,,,,interesting in a morbid sort of way