Debris in Crankshaft Cavity Below #1 (Mag) Cylinder

[orionz]

Rebuilding from a case of carb bolt down the intake/stripped rotary valve gear when I noticed the crank wouldn't turn freely. When I passed one particular place in the rotation cycle it would jam...otherwise it turned okay. Started peering around inside the cavity below the mag cylinder and found this little guy on the bottom of it. Appears to be a piece of an aluminum casting and it seems to show some damage from being banged around. I'm not sure what it came from BUT I know what it DIDN'T come from because I've still got these parts out of the engine. It's not from the rotary valve shaft or the rotary valve itself, nor is it from the rotary valve cover or the intake manifold that bolts to the cover...and I've checked the carb throat for missing pieces. All appear intact and the bolt that jammed the rotary valve was cut 2/3 of the way through...but otherwise remained intact. It didn't get farther than the RV. Any ideas where this might have come from before I tear the whole thing apart again? All of us are smarter than any of us! TYIA! Plz see pics attached...

 

[mikidymac]

If it is aluminum then it appears to be a piece of a piston.

 

[orionz]

If it is aluminum then it appears to be a piece of a piston.

Thanks for the quick response....assuming that to be correct would that require a replacement of the piston? I would guess that something in vertical reciprocating motion would not have a balance problem from losing a small piece??

 

[mikidymac]

Yes, absolutely a new piston. And that debris probably is stuck in the crank bearings (replacement required) and a damaged cylinder head.
The imbalance isn't the big worry, it is the cracked and damaged piston and debris.

 

[orionz]

Thank you!