Peening and fretting in roller bearing assemblies is very common.
In the early XS the small end was also roller bearing. Two chances to "bang the tune up".
The XS is particularly susceptible to over advance as seen in multiple experiences here and elsewhere.
All it takes is just a bit of roller bearing peening and there is no such thing as graceful degradation.
Somewhere on
@mrriggs dusty, dark, shelves of prehistoric dementia is/was an attempt at a plain bearing one piece crankshaft. The XS could benefit from a one piece crankshaft but the obstacles are numerous, complicated, and esoteric.
Back on thread. Blow the tune up on a roller bearing engine and the carnage has only just begun.
@gggGary , good catch! I have one more. Reduced back pressure (only time I'll use that term) or different resonance may allow a different pressure differential across the intake valve guide seals.
My alcoholic always puffs on a sharp throttle close, always. A good scavenging exhaust system will always "suck" ,literally. In order to get any lubrication to the intake there is clearance as well as an imperfect valve seal to allow lube. Even that isn't enough. Alcohol requires at least some top lube if not additional light lube in the oil system.
Enough rambling for now :- )
