Does anyone know the maximum overbore for an M116 Alpina? When I bought mine 20-odd years ago it had been left outside with the head off and no piston, just a sad rusty con rod flapping around in the cylinder. A quick measurement with vernier calipers shows the bore is already at 83.8-something mm, so probably was on second overbore (83.75) already, and it is quite rusty. It might just clean up to 84mm, but that could be wishful thinking. I know that at some point they went to a thicker liner that could be bored out further but I'm not sure when the change occured. Currently the liner is about 3.6mm wall thickness so would have been about 3.85mm or so when new. I see there are Wiseco pistons listed in .25mm increments all the way from 83.25 up to 87mm but I'm curious if I can bore this out again or if I should look for a sleeve. It is a 116 stamped barrel, but it's within the last ten produced so some specs may differ from the usual.

Inmotion in the UK list them up to 86mm if that's any help

My 138 Alpina is the model that followed the 116 and it has a standard-bore 370 Pursang piston in it whatever diameter that is. I don't remember what stamping the cylinder had.

Thanks, I only see M116 pistons at 83.70mm on the In Motion website, which is too small. They show M99 and Sherpa T in the larger sizes but those are shorter stroke so I'm not sure if they are compatible. I will have to check with In Motion and Hugh's.