Crankcase dimension help needed please

[sunrisemac]

I am having a play with a 185 cylinder and piston to try on my GP150 but the engine is still all up together at the moment.

I have done a wee bit of port widening and have re-machined a new Indian head I got in a kit when I first put the scoot together, I have matched the piston crown shape to the squish band and ring doweled the head to the barrel to maintain concentricity and now am looking at the geometric compression ratio.

I am hopeful that to enable me to get a bit further without taking the scoot to bits at the moment, some knowledgeable chap on here could tell me the nominal measurement, for a 1969 Italian SX casing, from the crankshaft centreline to the cylinder mounting face, my casing has not been changed from standard.

[Grumpy225]

Deck height can vary case to case. The good news is it's a very small variation and machining material off that part of the case is not normally done. If I was doing what you are doing I'd assume it was stock and make any adjustments needed once I had the top end off.

[sunrisemac]

Thanks Grumpy225, I'm not thinking of machining anything off the case but would like to know the nominal dimension so I can draw the setup on the PC and see what differences will be made for movement up and down with packers at the top and bottom of the barrel.
At the moment I have assembled the head and barrel with no spacing and done the head volume with the piston hard up against the remachined head, I can now calculate what variation I get in CR with measured amounts of squish and if I need to remove metal from the head or skim the face to reduce volume.

I have found a mate of mine has a case I can borrow to put on the inspection plate at work and measure up, looking at everything I have measured and drawn up so far I am thinking the nominal size might just be 75mm.

Cheers ian

[Grumpy225]

Ahh that makes more sense. Sounds like a fun project.