On Sat, 24 Apr 2021 10:19:32 +0100, AJH
wrote:

snip

With Nikasil lined cylinders it is unusual for the bore to get scratched
from seizing or "nipping up" unless a hard foreign object has been
ingested.

Agreed. I believe the barrels on both my BMW motorbikes and the
Merseschmitt are Nikasil plated.

What normally happens id the aluminium piston overheats and
partially melts, not only jamming the ring in the piston lands so it can
no longer spring out and make a seal but also the bore picks up some
aluminium.

Yeah. I used to spend quite a bit of time in the local motorcycle shop
(I was their voluntary 'IT guy' and they were personal friends g) so
seem loads of those sorts of things of the 'lads' of-road bikes.

Often you can get away with replacing the piston and ring but
you must remove the aluminium pick up in the bore, both chemically and
followed by a light hone.

Is there any chance any 'smearing' you / we see is the surface Nickel
being worn off till it gets to the Silicone Carbide in non seize
cases?

Cheers, T i m