Can anyone identify the thread on my '77 Commando 850. The oil level screw hole in the primary chain case has been 90% stripped out by previous owners. I would like to helical it so that I can re-use the original screw. I am not sure that thread there screw is. Part number 06.0389 in AN does not identify the thread. The screw is 3/8 OD, but I only have metric threads gauges. It looks like BSF but a strange thread for an alloy casing.
Its not in this database so…
Its not in this database so no answer for 06.0389 but most others are, so for future fasteners this is a good start.
(I have now edited the database so it is listed as 3/8 UNF)
http://www.gregmarsh.com/mc/FastenersList.aspx
Sadly BSF was a common thread form used by the British motorcycle industry into alloy when BSW would have been better. One of the worst offending application being the studs into the bottom of the Norton twin head which are a known stripped thread point. Best on these not to helicoil BSF but make some custom studs with UNC ends where the studs goes into the head and helicoil the holes UNC.
06.0389 is also the level screw for the pre mk3 primary cover, just checked one and it is as RGM say 3/8 UNF. Too fine by far for steel into alloy, looks like the surplus helicoils I have left over from the alloy seat knobs are no longer surplus.
- Log in to post comments
I also noted that the new…
I also noted that the new magnetised crankcase oil drain plug that I bought from AN had a different thread to the original. I will be sending it back.
- Log in to post comments
Pretty sure it is 3/8 UNF. RGM think so too.
https://www.rgmnorton.co.uk/buy/oil-tank-chaincase-drain-plug-with-magnet-3-8-unf-commando-stainless_1018.htm
You don't usually use a fine thread in alloy but it doesn't need to be very tight, just nipped up.