Greg/Bruce:
What I found was I caused this calamity. When I retrofitted the car with the leaded bronze bushing I made the bushing the full width of the bore.
While I still had clearance when the engine was cold, I believe when it got good and hot the aluminum case, expanding double that of the steel crank pushed the started gear on the crank hard up against the splined adapter. This in turn caused rotation and I think the heat generated got things going south and with heat clearance got tighter and well we all know the story from there. Ended up fusing the bronze main to the crank, it spun in the case again. When locked solid the starter gear spun the starter to destruction. Sprage unit is fine.
I just failed to analyze the design and allow for crank endplay pkus differential expansion plus adequate running end play for the starter gear. Never checked any of it. I did note on the inside of the starter gear the factory painted on with paint pen -0.003" which i'm not sure was referring to but it was obvious they were checking something. My bike at 307 should have the early crank and dampener, but it actually has the latter design which was probably put in as a test mule piece since this was a demonstration bike. It was the 14th bike assembled.
Now for some further information. On the spare engine I have, #204, I had torn it down to preserve. In doing so I noted it has the earlier crank and dampener. But I also, for the first time note some peculiarities with the starter gear set up. The machined boss on the outside of the case is larger than the boss on the starter sprage allowing it to bump up against either the bearing shell or crank. The shell is set flush on the inside of the case and sub surface or inset on the outside to allow for adequate endplay. I never could see this on 307 the first time as recall, the left side main smoked and had spun in the case. What I noted however, was even though 204 had 27 miles on it as received the starter gear boss was scuffed a bit on the inside inner corner. This says it was in contact with the crankshaft journal. Not good. Not saying it would survive but what is disturbing to me the factory allowance of gear to contact the crank. It should bear up against the case itself and never touch the crank or bearing shell. As designed it can contact the shell and bearing dependent upon which is closest based upon crank position and case expansion.
I'm planning on pinning the stock bearing shells in 204 and reassembling. Then I will probably modify starter gear and bushing to accommodate all motion and not get bound up.
Makes me wonder if the original 307 main bearing failure wasn't caused by gear rotation when case got good and hot.
