[snip] If a person reads all of Georges ramblings on this subject he will see that he knew that the bronze gear was more of a crutch than the fix. If he addressed backlash I don't recall reading it.
That's right. Since most gears lost teeth opposite the "00" mark that was stamped into the rim, it was thought that impact stress caused localized deformation, which lead to localized weakening. Soon, however, it became apparent that manufacturing inconsistencies made some engines loose teeth like a septuagenarian, while others seemingly ran forever. Joel spent a considerable sum of his own money having the gear profile analyzed, and the recommendation was to try making the idler gear from bronze.
Dave, (Xyzer) spent some time and measured a block accurately and turned up the fact that the idler gear shaft was mislocated in relation to the crankshaft and cam, and he was the first person to identify the issue of backlash as the likely cause of gear stripping. I don't recall anyone who installed the offset idler spindles that he made available for a time, having any further problems.
The Ashwamegh 6/1 that was my first engine, made a terrible "clack" as the engine cranked over each cam lobe without compression. After making a series of idler spindle bushings drilled offset 0.005 to 0.030", I found that the 0.010 bushing brought the backlash to the point where I couldn't hear the "clack" anymore. I used thickness gauges to measure the backlash, but because of the cramped quarters and difficulty of seeing into the crankcase, I wasn't very comfortable with the precision of my measurement. So I chose the bushing that eliminated the "clack."
For the sake of posterity, I'd like to understand how you measured gear backlash. I haven't read anyone describe in detail how they actually measured the lash.
Quinn