Apologies if this has been thrashed out before.......
A pal of mine and I were chatting yesterday and he asked if I knew when the BSA M20 tappet cover switched from alloy to cast iron (steel?). Now not having ever owned and M20 (much to my chagrin), I didn't have a cooking flue!
I'd be interested to find out the answer to share with him, so if any of you M20 'sperts could enlighten me, I would be most grateful.
I search on this forum indicated that mid to late war, there were changes, but I'm sure that there is more to this story than that.
Wasn't it the Ariel that changed from alloy to cast iron.
I believe the Ariel W/NG had a number of alloy parts changed to pressed steel during the war including the mag chain cover and the primary chain covers (inner and outer).
The Matchless G3L had the mag chain cover changed from alloy to cast iron and I think the Velocette MAF had some parts changed from alloy to cast iron possibly the gearbox end cover and the timing cover.
The Norton 16H had its tappet cover changed from alloy to pressed steel.
I think the only alloy item on an M.20 that was changed was the tappet cover which was cut from a steel sheet.
As a means of saving aluminum for more important projects, lots of bikes had parts made from steel instead, including the M20 tappet cover. Which as Keith stated was just a flat plate. Ron