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0.386" on a not new but not beat up switch. However, that does not tell you a lot because threads are truncated.
International standard is 10.287 mm (0.405") major diameter. Engineersedge.com gives 0.390" - 0.397" major diameter.

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Hi Dave, Thank you.

What do you mean by truncated? I thought we were talking about 1/8-27 straight pipe thread switch? I don't understand, what part is truncated?

My home made oil pressure test fitting is .3915 major diameter. It fits fine in the electrical nuts. My spare timing cover had dent at switch fitting. I tapped it out. Fits fine it that. It will not screw into my timing cover. Too tight

Next time I have switch out I'll reduce major diameter & see if it helps. Switch is working & not leaking. I'm kind of afraid to touch it. It might quit working...
Don


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Don -

I have an original 60-3719 NPS thread switch. This is Smith's Industries PS5330/1/03 (not Lucas).
Thread major dia. on mine is .388".


1978 T140E
1979 TR7V
1960 Royal Enfield Bullet 350
1973-81 (6x) Bultacos
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This problem looks kind of solved, though it has raised a number of peculiarities. Morgo (very helpful) tell me that Triumph used BSP threads on T140 timing covers intended for the UK market, and NSP for US market bikes. That ties in with what Kirby Rowbotham told me yesterday, which is that he used BSP fittings when making his oil filter kits. I have one on my TR7 and I've removed & replaced the fitting several times over the years. It is a perfect fit, not any kind of bodge where a BSP male thread has been forced into an NPS female.

LP Williams can also supply NSP banjo bolts with banjo-ended stainless braided hose, so I now have a choice of options. First on the list is to buy a Morgo BSP elbow fitting and offer it up to my timing covers (I have no idea whether they came of UK or US bikes).

Anyway, as is often the case when messing about with old Triumphs, things have been far from straightforward, but I've learned something!


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Originally Posted by Tigernuts
.
Anyway, as is often the case when messing about with old Triumphs, things have been far from straightforward, but I've learned something!

Ah, that would explain why switches (BSP....NPS. thread?) for whatever market all bear the same Triumph part no., then.......


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Originally Posted by Tigernuts
Morgo (very helpful) tell me that Triumph used BSP threads on T140 timing covers intended for the UK market, and NSP for US market bikes.

Absolutely incorrect. If that was true then there'd have been two different timing covers and two pressure switches. There were not.


https://www.britbike.com/forums/ubb...-on-t140v-oil-pressure-switch#Post706375
https://www.britbike.com/forums/ubb...itch-screwed-in-an-nps-thread#Post845818
https://www.britbike.com/forums/ubbthreads.php/topics/469550/re-oil-sending-unit-leak#Post469550

https://www.thunderbirdspares.com/oil-pressure-switch-triumpht140tr7-1974-1983-60-3719-uk-719-p.asp
https://www.britishmotorcycleparts....itch-veglia?gn=Search%20Results&gp=1

Last edited by L.A.B.; 05/16/22 12:58 pm.
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You could be right, and what you say is certainly conventional wisdom. I don't know. But I do know that anomalies in Triumph parts books aren't unheard of. They were still listing the tapered thread switch up to 1974 apparently, even though (again, apparently) Triumph changed from tapered to straight in 1970.

Only one way of finding out for sure and that's to get a BSP fitting and see if it fits properly (like the existing one in my TR7's timing cover, which Kirby assures me is a BSPP). I'll report my findings on here.


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Originally Posted by Tigernuts
You could be right, and what you say is certainly conventional wisdom. I don't know. But I do know that anomalies in Triumph parts books aren't unheard of. They were still listing the tapered thread switch up to 1974 apparently, even though (again, apparently) Triumph changed from tapered to straight in 1970.

The early switch thread was NPT and later changed to NPS but none were BSP.

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It remains a mystery for the time being. I've just spoken to Steve Campbell (about something else but I asked if he knew about this). He reckons what Morgo said is bollocks, and that the early ones were BSPT, changing to BSPP. I must admit, what Morgo said does seem rather far fetched, but it is what the chap in their tech dept said this morning.


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Originally Posted by Tigernuts
It remains a mystery for the time being.

No, it isn't as the thread has always been NP (T or S)



Originally Posted by Tigernuts
I've just spoken to Steve Campbell (about something else but I asked if he knew about this). He reckons what Morgo said is bollocks,

Well, he got that bit right.


Originally Posted by Tigernuts
and that the early ones were BSPT, changing to BSPP.

But yet, more bollocks, unfortunately.

The Smiths oil pressure switch from my UK market '78 registered T140V marked PS 5330/1/03 and 27 (thus NPS) TPI.
[Linked Image from i.postimg.cc]
My T160's switch is also 27 TPI.
Edit:
Also, although Triumph didn't see fit to mention the switch was American NP thread, it was in BSA manuals (two examples from different manuals, below and the second of which mentions a "copper/asbestos washer" that only a parallel thread would use).

[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

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Don, all threads have a truncated crest and trough. The tips and troughs of cutters are not a sharp V. On american threads they are squared off, on most British threads they are rounded. To compare threads you have to use V tips on a micrometer but you can do it with a pair of calipers if the chamfer on the tip has a small enough flat to get into the V of the thread. Mind, it is only good for comparing two threads.
Another method is the three wire:
Pitch diameter = Measured distance over the wires + cot (a) / (2 * TPI) - wire diameter * (1 + cosec (a)
a = half the included thread angle (30 degrees for american threads)
Wires should be within 0.00002" round and the three sizes should be within 0.00003". Best size for 27 TPI is 0.02138"
(machinists guide)

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To answer the comment on the first page, our kits come with 1/8" X 27 NPT, 1/8" X 27 NPS & 3/8 X 26

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http://www.triplesunlimited.com/index.php?route=product/category&path=70_60_66


"-Adapter on engine (banjo connector): it is connected to engine together with the oil warning switch, thread 25/64” 27TPI. (most commonly known as 1/8" NP thread)"

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Hi CBS, Thank you for posting the threads. That clears it up.
Don


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Hi CBS, Suppose owner wants to remove pressure switch entirely.

Do you sell a plug in 1/8-27 straight thread?
Don


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Try McMastercar

Also made this tech post a few weeks back, might help some

https://www.classicbritishspares.com/blogs/news/guide-oil-pressure-sending-units

Cheers

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"1968 Only 1/8" X 27 (NPT) 60-2133"

However, according to Triumph Corp. Service Bulletin 69/9, May '69, D2133 (60-2133) was the "Straight Thread" (NPS) switch that replaced the tapered D1943 (60-1943) switch for "All 1969 Triumph Twins (and 3 cyl. models after No. AC01629)".


https://www.britbike.com/forums/ubb...tch-npt-blanking-bolt-1973-t1#Post300527

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Originally Posted by L.A.B.

"1968 Only 1/8" X 27 (NPT) 60-2133"

However, according to Triumph Corp. Service Bulletin 69/9, May '69, D2133 (60-2133) was the "Straight Thread" (NPS) switch that replaced the tapered D1943 (60-1943) switch for "All 1969 Triumph Twins (and 3 cyl. models after No. AC01629)".


https://www.britbike.com/forums/ubb...tch-npt-blanking-bolt-1973-t1#Post300527


I have a BSA service bulletin that shows 60-2133 as tapered?

Bottom line, this subject is touchy, like in the post, measure your own existing cover to see what you have

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Originally Posted by C.B.S
Bottom line, this subject is touchy, like in the post, measure your own existing cover to see what you have

Me?
I've already posted that information and it's the normal T140 60-3719 NPS switch.

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Originally Posted by C.B.S
https://www.classicbritishspares.com/blogs/news/guide-oil-pressure-sending-units

I have a BSA service bulletin that shows 60-2133 as tapered?


"Triumph (All) 750 Triples 1969-1976 1/8" X 27 (NPS) 60-3719
BSA (All) Unit Singles 1969-1973 1/8" X 27 (NPS) 60-3719
BSA (All)Triples 1969-1973 1/8" X 27 (NPS) 19-6508 / 60-3719
BSA (All) 500 & 650 Twins 1970-72 1/8" X 27 (NPS) 19-6508 / 60-3719
"

As far as I'm aware, the 60-3719 switch wasn't introduced until the 1974 model year so what Triumph part number NPS switch did Triumph triples (or twins) have before 60-3719?

Also...
"Triumph Trident 1968 Only 1/8" X 27 (NPT) 60-1943 (60-2133)
BSA (All) Unit Singles 1968 Only 1/8" X 27 (NPT) 19-6504 / 60-2133
BSA (All) 500 & 650 Twins 1969 Only 1/8" X 27 (NPT) 19-6504 / 60-2133
BSA Rocket III / A75 1968 Only 1/8" X 27 (NPT) 19-6504 / 60-2133
"

BSA 19-6504 is Triumph D1943/60-1943 as both are 5307/05, not D2133.

BSA:
[Linked Image from i.postimg.cc]
Triumph:
[Linked Image from i.postimg.cc]


Therefore, logically BSA 19-6508 is Triumph D2133/60-2133, Smiths 5300/1/07 NPS as Stuart said in the previous link and quoted below, or there would be no NPS switch until '74.

Originally Posted by Stuart
Of all the original Smiths o.p. switches I've seen, each of the three different types supplied to Triumph and BSA has a different Smiths part number stamped on it - PS 5307/05 (taper thread, Triumph D1943, BSA 19-6504), PS 5300/1/07 (first parallel thread, Triumph D2133, BSA 19-6508), PS 5330/1/03 (second parallel thread, Triumph 60-3719).

Edit.
Also...

The 650/750 timing cover part number remained the same (E9246/70-9246) from '69 (DU85904) when the pressure switch was first fitted to the 650 until '77 T140 indicating the timing cover thread and therefore the D2133/60-2133 switch was NPS from the beginning and a change of timing cover thread without a change of part number in this instance seems unlikely.

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OK, here's an update on this if anyone's interested...

Morgo sent me a BSP fitting. It does screw into the T140 timing cover, apparently nicely. But the threaded section is only 5/16" long, so I guess there isn't enough thread involved for the mismatch to show up. Having taken on board everything people on here & elsewhere have said, I double-checked with the chap at Morgo. He backtracked from saying Triumph made two different timing covers and used two different oil pressure warning light switches. This time, he said he only assumed that because so many people buy BSP fittings for their T140s, he thought some must actually have been made with this thread. In fact, it seems that people have been buying and fitting them without knowing they're not technically correct.

He was good about it though and is sending me an NPS banjo bolt with a 90 degree adaptor free of charge. So, the question is finally resolved - L.A.B and others were right, the thread is NPS in all T140 timing covers. It would have been better not to have been led down the garden path but hey ho.


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