750SF2 - Strange ?engine? noise when under load

The twisting play in the pins-smallends sounds very odd, but I reckon could definitely explain the noise. Do you think it's bad enough to warrant repair? That would involve pulling the ends off the crank, and by then you may as well fit Carillo or Arrow rods (which i think Red could supply). Big ends clearly not an issue.

You'll need to determine how the piston height and crown have altered compression ratio. Most accurate is to burette the chamber on an assembled engine, so that will have to wait. Those pistons don't look like they've done many km at all.

That's considerable sideplay in the rocker - easy fix is to carefully grind the shoulder on the pin so it fits further into the head and reduces the gap to the rocker. If you're handy you can set up an accurate 'jig' with the pin in a lathe chuck (ideally) or a pedestal drill chuck, and mount an angle grinder securely to either the cross slide or drill bed and grind away as required.
 
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for anyone with the similar JE pistons stamped 463098, some data. looks like they have good pedigree. surprisingly old for how they look.
notes from JE: ring part number is XC8050, piston to wall clearance is .0015” at .500” from the bottom of the skirt. Ring end gaps should be top .013”, 2nd is .015”, oil should be good where it is at.
 

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