M8 Performance

6500 rpm isn't high rpm in a race motor, but, the issue lies more with chamber shape, as a 4 valve motor should be a pent roof and not a hemi or semi-hemi design. A good 4 valve head would be a shallow pent roof with little included valve angle, and a center spark plug. Compression would be a flat top piston and piston height would be what determined compression ratio, not a high dome piston. But, that shallow pent roof would make the heads taller to contain the rocker gear and valves standing up, which makes a packaging problem in a motorcycle engine..

I wonder why there wasn't a feeler gauge check for piston to wall clearance before assembly, would have save a lot of heartache!

As short lived at that was, it looks like poor preparation during pre-assembly, that is signs of dirt in the cylinder or on the piston that didn't get properly cleaned, those vertical streaks look like something was broaching the cylinder wall. those 2 oval spots about a 1/3 of the way down the cylinder look like a distortion created tight spot. That motor would need the cases split and everything cleaned and all bearings and seals replaced before being used again. Hopefully they will save you time by replacing the whole engine. What does the combustion chamber look like? Does it show signs of metal bouncing around?

That would be easier to start with a new block as they will have to strip it all the way down, put it all in a dishwasher, and inspect every moving surface for damage then build back up with all new bearings. Had a roller lifter turn (broken tie bar) in a Wedge motor decades ago, 30 seconds and wiped the lobe off the cam, had to pull the motor down and wash everything, lucky the metal only made it to the oil pan and not sucked up the pump, new cam, lifter, tie bar, gaskets and the motor was ready for the track.

I would make the small one match the others, that way sometime in the future they can't get mixed up.

That would be fun in any bike, just don't look for a lot of fuel mileage!

Bet he doesn't want to tangle with a turbo Busa though! I've seen local ones making well over 300 hp on low boost, street driven.