Thta's a good point, Rocketman. I remember that the BS90 DeLuxe that I owned back in the day (1970) had a brown fiber drive gear, not white plastic. I had sheared off the small casing drain screw (thinking it was a case retaining screw), and when I tried to rdrill out the stump to use an "Easy out" screw extractor, teh stumpwound itself right in against the pump gear and made a hell of a noise when I started the engine! My brother helped me to remove the case and investigate, and I remember the gear was brown fibre material, and one side of the teeth has been neatly machined away by the drain screw. I removed the stump of the screw and reassembled everything, and the bike survived for a further 2 years until I sold it. I'm not sure a plastic gear would have survived such treatment.
Presumably, a fibre type gear will always be more resistant to cracking, being a composite material. All of the 350 engines I have seen have had white plastic gears, but I can't for the life of me remember what type of gear my TMX has got. Looks like I'll taking the cover off to check!
