Yes, clearly that would be the definitive method of working out the size. Unfortunately when i had the sump off i was slightly pushed for time and working in the dark. But i guess it should be possible to get a stoke/bore measurement from underneath without taking the head off.

Clearly the OPs head is (or was 6 months ago) off mines not and you can really get a good line onto the piston through the spark plug hole for the sort of accuracy that would be needed to define the stroke as being that of a PE 1900 or a normal 1600.

Otherwise it would also be possible, for the cost of a head gasget, to take the head off and be done with it. While also confirming the TDC mark. Probably replacing the bolts with non-stretch bolts.


Daniel