Originally Posted by
GallopingGhostler
Judging by the wear pattern in the disk's crank pin hole, one can see where that the collar like lip on the connecting rod is almost nearly fully seated in the hole. There is some wear at the bottom of the hole from the crank pin. Thus, it seems like it is working as it should.
This engine has never been run. The pattern in the disc hole is from the machining alone, not sure why they made it oval (shouldn't be needed?). The work in the mill, with a non-flat tip on the tool, gives a protrusion in the center of the hole and the useable depth is about 0.7mm.
If one holds the backplate in place with the crank-pin on the disc, rather than in the its hole, there is gap of about 0.3mm (less than 1/64") between the crankcase and backplate. This would then be the amount of pin that is in side the hole when the engine is assembled correctly. With a chamfer on the pin of 0.10-0.15mm, there is very little left to drive the disk.
One could possibly improve on this a little by shiming in front of the crankweb, I guess, or remove some material on the sealing surface of the backplate (in a lathe). But I wouldn't run it as it is now...