Wow.
On #4, that's all below the oil control ring.....like the piston was trying to seize in the bore.
However, that's not the "big dimension" of the piston.

That's more of a "thrust" issue...
Can you take a picture down the length of an installed (pair) of connecting rods, to show how the rod is centered in the piston?
If a Chevy design rod, it will not be centered. And sometimes, due to cylinder location, a rod may be actually rubbing on the wrist pin bosses of the piston.
This pushes the piston into the wall of the cylinder...which is what #4 appears to have done.

 

Yeah, you're light years ahead of this stuff!
The "early stroker" stuff.....all the way through Phil Threshie, was done by people that missed the entire book of "Basic Engineering Principles of the Internal Combustion Engine."
Most of these engine ran for very few hours.

You have any idea how many miles were on this engine?

 

The shortest one I ever heard of, was a Carl stroker in the UK that clocked minutes.

 

Kevin,

Rather than speculate about issues that would seem to be unique to this build surely the person who built this engine must be known given the car has a discrete name and thus maybe contactable to advise about the logic behind the build details? Quite possible the builder may not be with us of course but...?

 

Rennsport in FL. The PO reached out to them during his years of ownership as well as Ken Geljack. They a have no records of what went into the engine.

So, all that is left is speculation.

I have heard from another member that the pistons are referred to as pancake pistons.

I'll get more pictures today.

 

Kevin,

i have been round these 928 shores for some 23 years and whereas I have heard the name I had no idea they were associated with building special 928 motors. I have a feeling GB would be able to tell you every nut and bolt he put into each and every motor he ever built.

 

They are/were a Mercedes engine building shop from what I heard.

I think it's wholly unfair to compare any other engine builder to GB.