Need help ID ing Mcculloch motor. Mc100?

[Scott Kneisel]

Hey all, just acquired what I think is at least a Mc 100 from a swap meet and I need some help making sure that is what it is.  Found the thread about the difference in engines, but still have some questions and facts about my engine. First of all the bore is 2.265 and stroke is 1.835,  one large exhaust port that appears to be stock, and has the recessed copper head gasket. I am assuming this to be a Mc100 with rebore of .015? since mc 100 bore is normally 2.250 and 101's are 2.280?
 
Does not appear to have a serial/model#. It has a BDC 14 carb and has the chrome flywheel shroud. other then the shroud chrome flaking off, it appears to be in great shape.

Any assistance would be appreciated. Thanks, Dean.

Mc100 would have a part number stamped next to the oiler nub on the back side of the crankcase.  The part number for the Mc100  block is 47873B   Some later Mc75 blocks have 47873 stamped but the 100 has the B added.

The block also definitely does NOT have a recessed head gasket unless someone added it and the crank PTO has RH threads and a key slot.  None ever had LH threads which didn't arrive until a few years later with the 101AA.