Jockey Journal Forum banner

WARNING! Triumph Oil Pressure Switches

24730 Views 40 Replies 19 Participants Last post by  Landon
Hello fellow JJers. I have been reading this thread for some time and am concerned about the advise given for Triumph oil pressure switches. The problem I see is that some JJers are advising other members to install the wrong type of sender or adapter for an oil pressure gage. First off DO NOT use a tapered thread oil pressure sending unit or a tapered thread adapter for an oil pressure gage. Triumph oil pressure switches are a straight thread, not tapered. If you use a tapered oil pressure switch then there is a good chance you will crack your timing cover. When I was a Triumph mechanic back when the factory was on strike we could not get many parts. Only what was on the shelves at the distributer. Once that supply ran out we had to make due with what we had. I can remember my father taking an American made automotive type sending switch chucking it up in a lathe cutting a shoulder and turning the straight threads.
I hope my advice opens up the doors for discussion so this problem can be corrected.
Old Codger
1 - 3 of 41 Posts
2. from *during* the '69 season 'til the end of Harris Bonneville production ('85?), the original thread was 1/8"NPS (American National Pipe Straight; i.e. 'parallel') (note: being a pipe thread, the 1/8" refers to a nominal internal diameter - the o.d. is roughly 3/8");

3. however, for a short period at the beginning of the '69 season, some engines had 1/8"NPT (National Pipe Taper). The only documentation I've seen on this refers to the the T150 engine up to number AC01629; however, I've an early '69 T100R in my garage with a 1/8"NPT thread.

But (and it's a J-Lo ) ...

... we're talking about engines that are at least over 20 years old and could be twice that, with all that implies in the way of d.p.o. Both 1/8"NPS and NPT are 27tpi whereas 1/8"BSP is 28tpi and, as I've mentioned above, 3/8"Cycle is 26tpi (not to mention M10 x 1.0 is 25.4tpi ).

From experience, I would say extract whatever's screwed into the o.p. hole of your specific engine and check the thread *very* carefully with both thread gauges and a micrometer (ime, any taper is actually quite difficult to detect by eye ). In this, ensure you actually have a 27tpi thread gauge - don't try and interpolate between the 26tpi and 28tpi ones because it's very difficult to do, even under a magnifying glass.

Finally, btw, be aware that there isn't any such thread as BSPP (BSP Parallel) (or BSPS - BSP Straight) - 'BSP' is parallel/straight by implication, a tapered BSP thread is denoted 'BSPT'.

I'm pretty sure this is by Mr Healy, which I copied a while back, hope this helps.
It sure would be possible these old threads have been altered to suit whatever fitting was at hand.
See less See more
Not here to knock you mate but if I were to have a knob like that (is it oil filled) which is a taper in a straight thread it would be safe to have it supported at the other end knowing how the trump vibrates.
I used 1/8" nylon to feed the rockers (like norton use) it's a cleaner look. When I took the original oil tank out I'm positive the hole is 1/8" not 3/16" so I didn't think much of it, I've only put 40 clicks on this build and it's a good reminder Hartz to check that sucker cause I ain't yet but I will.
1 - 3 of 41 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.