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WARNING! Triumph Oil Pressure Switches

24734 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
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So, what is the deal with this? I too have heard and read all sorts of crap including that some early models have tapered threads and some later models (not sure the year cut off) have straight threads.

because the plug in mine felt a little sloppy and I noticed that it doesn't fit that well (loose and feels like it is the wrong fit) I slowly screwed a 1/8" BSPT to 1/8" NPT adapter in mine, but stopped as soon as I felt resistance. I do not want to crack the cover. It's a 71 650.

Flypa38, what did you end up getting PN etc?
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.
Holy crap, that is some serious info!:eek: Ok, so, I have no idea what I really have because the plug that came out looks stock, but didn't feel as if it fit correctly. It didn't leak, but it didn't really tighten. Felt stripped and very sloppy. So, I don't want to rely on that. What I have in there now is a Sunpro gauge adapter that is a BSPT to NPT. Very carefully and slowly, I gave it a go. It screwed right in and tightened up nicely. So, with that said, it might not be the correct threads, or I made new ones not by choice, but it's in and everything seems fine, tight, and not cracked. Who the fk knows at this point? I just want to ride the effin' thing instead of worrying about it all the time and dealing with one crazy abnormal situation after another. :rolleyes: I've had the bike for about 2 months and have ridden it like 5 times. The rest of the time I've been dealing with carbs, stripped threads, valve adjustments (normal), and now a mystery thread issue on the timing cover.

Thanks for the tips and for sharing the knowledge about these quirky bastards. :eek:
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As I've always understood it, British pipe thread is 'parallel" not tapered like "our" pipe fittings. That's why Autozone oil guage fittings split Triumph timing covers.

Research it -
Dragon, that first listing has some good info. Looks like it doesn't matter tooooo much to mix different standards as long as the pitch is correct and thread sealants are used. I used a tiny amount of high temp permatex sealant on the last few threads of the fitting. Def. don't want to get that in the oil flow.
Here's my gauge:

Works great and the oil pressure is excellent!
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I've run them like this on previous bikes (non were Triumphs though) including drag bikes. Actually, you can see the gauge with a quick glance down there. Can't really see the numbers, but as long as the needle isn't near the bottom, all good. I mainly use it on start up and then watch as the oil warms up and the pressure drops. As soon as the pressure drops to normal operating pressure, she's all warmed up and ready to go. Then, once in a while, I have another look while at a stop light. Obviously, it's not meant to look at constantly. It's mainly just to check periodically to see how things are going. I don't have a problem not running a gauge, but I think there is more risk to place a gauge on there periodically (multiple threading and unthreading) like the Triumph manual recommends, rather than permanently.
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.
Yes, it's oil filled. The adapter used is a BSPT to NPT fitting which is the only thing I've found that actually screws in nicely without abnormal resistance.

See, that's the problem. Nobody seems to know for sure what type of threads these have. It's a 71 650 and I've read and heard that it's straight, NPT, BSPT, parallel, bla, bla, bla. So, I suppose the fear is that the vibes will be too great with a heavy gauge like that sticking out, so the metal will fatigue and lead to a crack or broken fiting, correct?

Ok, enough of the horror stories. Thanks for all the concern. I've run gauges like this before without any problems, but Triumphs are new to me and I wouldn't doubt it that the horror could come true. So, once I find out what threads this is, I'll get a small bolt or plug to put in there.

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