I'm rebuilding a 1969 BSA A50 (my first). VIN EC21861 A50R
The old oil pressure switch was almost rusted out of existence so I ordered one using the part number in my parts manual. Problem is the new switch will only turn in a few turns, while the old one will screw all the way in. I've searched the web and have discovered language about tapered and non-tapered threads. My caliper sorta leads me to believe that the old one is a tapered thread and the new one is a non-tapered thread.
My questions are:
- can anyone confirm that some of this vintage had tapered threads?
- what do I order as a replacement when the parts manual lists the wrong p[art number?
Thanks.
Parts servicebulletin G59from October 1969 may explain. See the last section.
Quote from: ramwing7 on 28 Mar, 2019, 21:24
My caliper sorta leads me to believe that the old one is a tapered thread and the new one is a non-tapered thread.
I had exactly the same thing with my 1971 A70 engine that I recently rebuilt. The switch that was in, looked like it was the original and was definitely tapered. The new parallel switch would only go in a couple of threads so I bought a tapered one and it went in all the way up to the 'O' ring seal that they come with these days so I used that one, although I was sure it wasn't correct as Julian has pointed out. If I had forcibly screwed in the parallel switch it might have ended in tears and I didn't want to risk it.
The problem with the tapered switches is that they will easily crack the crankcase if over tightened as happened on my 1971 Firebird. I sent it off to SRM, who did a very nice repair weld to it when they converted the Timing side bearing and used a parallel thread.