Ok so from what I am seeing is the pistiondia from the small dia crankcase engine measures 1.306. what is the dia of the piston from the engine with the large dia crankcase?

if you have the crankshafts out try and measure the stroke.

If the stroke and the dia of the piston is the same the cc is the same.

You may be able to measure the stroke with the crank in the engine measure with the depth part of you caliper from the cylinder base to the rod journal at tdc and then again at btd. the difference is the stroke.

I think what is happening is with the Larger dia crankcase set up it has a longer rod. It has to as now the cylinder base is higher in relation to the crankshaft center. the enngine with the smaller crankcase has a cylinder base that is lower in realtion to the crankshaft center than the other engine and therfore needs a shorter rod. the original rod must be used with this engine and cannot be interchanged between the two crankcase sizes.

Ok so look at the pistons. Are they the same? is there a difference in the rod lentghs? Take the piston you want to use and install the short rod from the small crankcase engine to this piston. This should now work but i dont know for sure as I dont have the parts in front of me.

Ajonr I see your in hutchenson KS. I can come get the parts and it will give me a chance to look through what you have and we can also do some comparisons with what you and i have. My brother lives in andale and I would love to come visit him to.

I will be intersted to see what you find on this crank and rod set up