What year did they change from cotter key to lock washer?
You're talking about the crankcase bolts? From the encyclopedia: http://www.mtfca.com/encyclo/doc25.htm
""On Dec. 2nd, 1924 Mr. Martin and Mr.. Galamb O.K.'d building motors with no cotter keys in the bolts but using lock washers instead in the crankcase, transmission cover and cylinder block assembly only. Why not put this on the blue print? Please advise."
Thanks Roger, just the information I was looking for