Inlet valve kissed piston on tickover

[Red Gauntlet]

Just ran up the 80CS for the first time and the oil had just started to come through into the tank when the engine suddenly stopped and seized, I had primed everything with oil and sloshed some down the pushrod tubes for good measure. After a minute it unseized and happily started again, took the head off half expecting a scuffed piston but instead found a couple of witnesses on the crown from the inlet valve. The valve is not bent nor scuffed in any way but I have swapped it out as it now has a small chip on the rocker contact face. It was not the valve that had seized but I fear maybe a follower, they were not tight when fitted but had the expected feel to them ~ unusual? It has new cams, followers and valves everything else is original on the valve train. This is a first for me on any bike I have owned. I don't want this to happen at speed as the PML piston will be damaged along with my bank balance. Pictures of inlet valve and stem.

[clive]

Not a G80 CS owner but I believe the model uses no head gasket, only the head lapped in. Is it possible the head has been skimmed and it has caused problems as there is now insufficient clearance for the piston. Not sure how a touch on the piston which did not bend the valve would cause a seizure.

[g80csp11]

G80cs piston.png

new cams should not be a problem , maybe mistimed!
Assume short stroke post 1960 engine , as the piston changed
Did you get the correct one for engine ?

[Red Gauntlet]

Yes, It's a '64 engine, everything correct to the book, all measurements within tolerance, it does have a head gasket but it was only ticking over so not much inertia there, just went stop, and would not kick over, valve must have stuck open holding the piston. It is timed correctly with a degree disc, built many engines bike, car and aero but never had a valve kiss a piston before after rebuild. Gave it a minute and it was up and running again, I thought the piston had picked up until I stripped it down, but it is like new. I rode it about 2 miles before the rebuild it so I know all the parts work together. Looks like this is probably a cam follower (tappet) problem, is this a known fault or am I just unlucky?