Rookie needing assistance

I would not be so quick to blame the piston. There are other issues that may cause valve interference. Timing, incorrect head gasket thickness, etc. I always use clay to check valve/piston clearance on assembly.

The squish band looks not very deep....is it .120" deep? or combat like .080" or less?
The valve seems to have stuck open after the guide/valve stem got gooed up or to hot. (E-10 fuel in a fiberglass tank?) The piston cooperated by smacking the valve back shut since it was misbehaving. Oh sorry for the bent valve said the piston.....
Begs the question cast iron or bronze guides?????
Who did the valve job?
Do "they" have a lot of norton twin experience?

added: is this a result of a hobot like 8000rpm missed shift? LOL
what are your valve spring pressures closed /full lift did your valve job guy give you the data?

o1racing03 said:

I would not be so quick to blame the piston. There are other issues that may cause valve interference. Timing, incorrect head gasket thickness, etc. I always use clay to check valve/piston clearance on assembly.

Click to expand...

Cam Chain tension?

free play in cam chain should be no more than 1/8"?

Ouch. Who put that top end together without checking clearances ? British motorcycles mechanics 101.

Your tread title suggested a new to Norton person.

The British engineering industry had an occupation called a fitter. Not a position known or necessary for Japanese manufacturers.

A fitter basically fits stuff. Almost nothing available for British machines either then or now fits without filing, scraping or other hand modification.

Check clearances on everything because most things will need a bit of rework.