The Triumph Dolomite Club - Discussion Forum

My understanding is the bore of a standard Sprint engine is 90.3 mm.

A piston that measures 89.69 mm at the crown, and 90.25 mm at the skirt, is therefore a standard piston...is it not?

Yes, that is correct.

Thanks Geoff, I thought so. They were sold to me as +20'

An oversize piston should have a stamping on the crown which indicates the size.