Originally Posted by DMadigan
...With the changes from BSC to SAE around '68 I did not know if the cam thread changed. Just giving 1/2" BSC does not give the thread pitch.
Phil, could it be your pattern 24-7000 was UNF, not BSC? UNF has truncated peaks, not rounded which may have interfered with the BSC cam thread.
Hi David,
the parts-# for the nut for A65s has been the same from 1964 'til the bitter end, so I suppose they never changed the thread for the cam shaft nut.
I am even inclined to think the differing parts-# for 1962 (sorry no 1963 sparts list available here) is more like linked to the nut form or surface treatment than to a differing thread.

The spare parts list states the thread to be 1/2 BSCyc, whilst the conversion tables attached to the workshop Manual list the 1/2" BSCyc thread to be either 26 or 20 tpi.

Prior to re-cutting I had tried the nut on two used camshafts and one brandnew SRM cam but couldn't get the nut to catch.
After having re-cut the nut's thread with a 1/2" UNF tap the nut could be screwed on all of the camshafts I have easily.

As stated previously, 1/2" UNF has the same thread angle and pitch as the BSCyc thread in question, so I opted for the bodge to ignore the rounded peaks in order to get the cam pinion on.
Surely, this is not how the makers intended but fair enough for me.

Best regards

Ph.

Last edited by Phil in Germany; 04/23/20 5:57 am.

Best regards
Phil
Duesseldorf/Germany
'62 A 65 Star (disassembled)
'69 A 65 Lightning
'71 A 65 Firebird
'84 Yamaha SR 500