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Allan G Offline OP
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So. I have a set of cases which has had the wrong oil pressure switch fitted. Despite ordering the correct switch I didn’t check the thread, and it was indeed a taper thread switch. I have since fitted the correct switch but the taper switch did damage the thread somewhat. The NPS switch screws in tightly but only if the crushable copper washer is omitted. I fear that this won’t be enough.

Annoyingly, you can get BSP and NPT timesert kits but there is nothing for NPS (not even a wire thread insert and I know a wire insert isn’t the right way to to seal a pressurised thread).

So I’m stuck for what to do.

The NPT timesert kits look to have an NPS outer thread, but it will still be a taper internal thread. But I could fit a taper switch with no worries of the thread being damaged further.

I could go the BSP timesert kit, but then I’m looking to what switch would fit.

Or I could get the 1/8 NPTF tap and see if I can clean up the thread so the taper switch fits best. (That would be the cheapest option)

I could suck-it-and-see. There’s a chance that there’s enough thread to hold it, I did apply some loctite 542 to the thread when fitting. It might never blow... or it could act like a 50psi cannon when it does.

Has anyone else had this?


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Or I could get the 1/8 NPTF tap and see if I can clean up the thread so the taper switch fits best. (That would be the cheapest option)


Yes.

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Allan G Offline OP
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Thanks Nick, I wasn’t sure if that was a wise option or not. There must have been a reason why BSA switched to an NPS type switch and I didn’t know if the NPTF was not suitable for screwing into aluminium or something like that?

Would the NPTF switch want to seat all the way flush with the case like the NPS switch does or just until the switch is tight in the thread? Being NPTF it should be self sealing as I understand it (although I’d still feel more comfortable using a liquid thread sealing compound).

Still happy to hear other opinions on the matter.


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The switch should seal without any help if it's a taper fitting.
My opinion on this is that they should always have used a taper fitting
across the group. That way there wouldn't be so many damaged triumph
timing covers around and one switch could have served all the bikes.
(when you screw a taper switch into a triumph cover it breaks the casting.)

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Originally Posted by Allan G
Would the NPTF switch want to seat all the way flush with the case like the NPS switch does or just until the switch is tight in the thread? Being NPTF it should be self sealing as I understand it (although I’d still feel more comfortable using a liquid thread sealing compound).

Still happy to hear other opinions on the matter.
For some reason straight pipe threads are rare in this country. For most applications it is quicker and easier to simply tighten the fittings without the need for sealant or tape.
Problems arise if one tries to screw the fitting too tight, it only needs to be tight enough to deform the threads enough to seal. I can't say why the new switches come with a washer, it is not needed. Seems to me that the washer only tempts people to overtighten the fitting to get the washer flush.


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Hi Allan,
Originally Posted by Allan G
set of cases which has had the wrong oil pressure switch fitted. Despite ordering the correct switch I didn’t check the thread, and it was indeed a taper thread switch. I have since fitted the correct switch but the taper switch did damage the thread somewhat.
Firstly, a specifically-NPT switch shouldn't have damaged a NPS thread - in the days when Wikipedia had the dimensions, the maximum OD of NPT and NPS were the same; someone better equipped than me needs to say whether NPTF and plain old NPT are the same or different.

If NPTF and NPT dimensions are the same, the oversize switch that damaged the case NPS thread was just one of the crappily-made ones that've now been around for a couple of decades. crazy

Originally Posted by Allan G
The NPS switch screws in tightly but only if the crushable copper washer is omitted. I fear that this won’t be enough.
can get BSP and NPT timesert kits
stuck for what to do.
You don't say what the cases are for? Not a triple, why don't you try wrapping PTFE tape around the switch thread; only worry about Timeserts and similar if the PTFE tape doesn't seal?

Originally Posted by Allan G
must have been a reason why BSA switched to an NPS type switch and I didn’t know if the NPTF was not suitable for screwing into aluminium or something like that?
The first engines with OP switches were the triples, they started off with NPT. Risking starting an internet rumour, it's possible Meriden had trouble making the tapered thread in twin timing covers consistently, given how little material there is; perhaps they were scrapping too many timing covers? Then the BSA buyers simply wanted one switch, so they could order larger quantities and ask for a bigger discount?

Originally Posted by Allan G
Would the NPTF switch want to seat all the way flush with the case like the NPS switch does
It appears so, given as I say, NPT and NPS OD maximum were supposed to be the same? Certainly there's a US Triumph Service Bulletin showing a NPT switch could be fitted in a NPS 'ole just with the addition of a sealing washer.

Originally Posted by Allan G
or just until the switch is tight in the thread?
Unlikely, given the fragility of Triumph twin timing covers and the average home bodger ...

Originally Posted by NickL
The switch should seal without any help if it's a taper fitting.
thumbsup

Originally Posted by NickL
My opinion on this is that they should always have used a taper fitting across the group. That way there wouldn't be so many damaged triumph timing covers
Only if all taper switches could've screwed consistently all the way into into all Triumph twin timing covers; any switch diameter larger than the maximum hole diameter buggers a Triumph twin timing cover; that's what the current switch maker either can't understand or can't be bothered about. mad

Originally Posted by NickL
when you screw a taper switch into a triumph cover it breaks the casting.
Only if a switch has a larger OD than the timing cover hole. The original NPT switches I've been given fit into NPS 'oles.

Hth.

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The O.D. of a NPT and NPS may be the same but the root of the NPT becomes imperfect at 0.2639" from the end of the male thread. Screwing in a NPT male into a NPS female too far will start distorting the tip of the female thread, pushing the female hole outward. Replacing the NPT with a NPS will feel loose from the distorted thread.

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There are four of my Triumph engines with NPT fitting screwed into the Triumph timing cover...no cracked cover, nothing distorted because even a hillbilly like me knows to use proper sealer and not reef down on fittings....Geez, it's that simple..... crazy


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons.."I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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Originally Posted by Hillbilly bike
There are four of my Triumph engines with NPT fitting screwed into the Triumph timing cover...no cracked cover, nothing distorted because even a hillbilly like me knows to use proper sealer and not reef down on fittings....Geez, it's that simple..... crazy


Unfortunately, the blokes who undertake this operation tend to overdo the tightening, hence
the abundance of broken covers around. Remember 99% of people are morons, you being
in the 1% is definitely not a true depiction of the typical triumph rider.

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Hi Dave,
Originally Posted by DMadigan
The O.D. of a NPT and NPS may be the same but the root of the NPT becomes imperfect at 0.2639" from the end of the male thread. Screwing in a NPT male into a NPS female too far will start distorting the tip of the female thread, pushing the female hole outward. Replacing the NPT with a NPS will feel loose from the distorted thread.
thumbsup Thanks for the clarification.

Is the "imperfect" male thread accommodated in a NPT female thread, or is that length useless? Reason I ask is the standard OP switch thread is only about 3/8" long, that'd be a lot of apparently-useless thread on a NPT switch ...

In engineering terms, what's the point of the "imperfect" thread? Is it possible to make NPT switches with less "imperfect" thread length?

Regards,

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Allan G Offline OP
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Some great replies,
Stuart, your right to ask which bike (I often chastise others for not adding that information) it's a 1971 A65 which should use the NPSF thread.

Aiui the difference between the NPS-vs-NPSF or the NPT-vs-NPTF is the F stands for fuel(s) and the thread seals completely when tightened. According to the service sheets the NPS type threads at least should be of the fuels type (aka dry seal) link showing comparison

I think it has been mentioned before that many sellers don't really know what they are selling. I noticed FEKED list the same switch against both Smith's part numbers for the NPSF and the NPTF switch, however it does state tapered on their site. Draganfly (where I got mine from) don't distinguish either way. You buy under the correct part number and you hope to receive the correct switch. You receive a switch in an LF Harris box and unless you have the lack of faith in the first place and check it, the average Joe would do as I did and have faith that it was correct.

It wasn't that the thread was tightening up that made me think there's something a miss, it was that it didn't (and I'm not talking about swinging on the spanner like a monkey on a branch either). What I cannot say for certain is what the threads were like from the previous use (I bought as a set of engine cases), so as I didn't check before hand I can only assume that they were fine before hand.


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Allan G Offline OP
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Originally Posted by Hillbilly bike
There are four of my Triumph engines with NPT fitting screwed into the Triumph timing cover...no cracked cover, nothing distorted because even a hillbilly like me knows to use proper sealer and not reef down on fittings....Geez, it's that simple..... crazy


As mention HB, I didn't reef down on the fitting, the nps switch still fits and tightens but not on all the threads. If you read my first post I'm also using a medium strength thread sealer (not thread lock).

I would prefer to use the correct thread for the bike/engine, though you cannot clean up an NPS thread if its damaged already.

I would imagine there is just as much meat on an A65 as there is surrounding the threads on a triumph casing. My casing isn't cracked, the threads are just not as good through a good portion of the case as they should be, and I don't feel confident that they will give the adequate support over a period of time.



Stuart, I have NPT and NPTF taps so I can measure the OD at each end of the taper.

I'm not a fan tbh of using PTFE to pack out a weakend thread, I'll take some measurements when I get chance and report back.


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Allan, with a tread locking sealant you should have no problems...Time Serts are quite expensive....


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But a V8 engine is a good start for me
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The imperfect thread is how a NPT seals, closing up the space between the male and female threads by distorting them.
Incidentally, some missiles use a NPT thread to attach the nose (although a buttress profile instead of triangle) because it insures a seal and the nose aligns with the body.

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Hi Dave,
Originally Posted by DMadigan
The imperfect thread is how a NPT seals, closing up the space between the male and female threads by distorting them.
Thank you; as Allan linked?

Originally Posted by Allan G
Regards,

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Hi Allan,
Originally Posted by Allan G
1971 A65 which should use the NPSF thread.

the F stands for fuel(s) and the thread seals completely when tightened. Zccordi g to the service sheets the NPS type threads at least should be of the fuels type (aka dry seal) link showing comparison
Hmmm ... I would've said Triumph and BSA used just NPS thread? I understand the mechanics of "Dryseal" but, steel switch screwing into ally, "Dryseal" theory was never going to work in practice for any length of time.

Originally Posted by Allan G
noticed FEKED list the same switch against both Smith's part numbers for the NPSF and the NPTF
Ye-ea-ah ... Feked is scary-bad:-

. '74-on 60-3719 - Veglia? They were made by Smiths before '79, Veglia only made 'em after Smiths stopped. 24 tpi or 26 tpi? Originals were 27 tpi NPS ... shocked

. Apart from that, the Triumph 60-2133 number is just the standard trade confusion. The original Triumph equivalent of BSA 19-6504 was D1943 (60-1943). Used first on the triple engines, first built in June 1968. That is a taper-thread switch.

. Meriden then caused the monumental part numbers confusion by printing D2133 in the '69 twins' parts books but fitting some of their early '69 ones with taper-thread switches. When the Triumph triples changed to straight-thread switches is recorded as January 1969; Meriden issued a new parts book around the same time, with D2133 for the switch ... Meriden failed to record when they changed the twins from taper- to straight-thread but afaict before they started using the date-code-5-figure-number VIN format in October 1968.

. Educated guess says Rocket 3's changed from taper- to straight-thread switch (19-6504 to 19-6508) around the same time as the Tridents; however, is there any record of when the '69 BSA twins did?

Originally Posted by Allan G
Draganfly (where I got mine from) don't distinguish either way.
Draganfly is just confused (reflecting they're fairly recent Triumph and BSA dealers) - if you look at their entry for Triumph 60-2133, it's the same switch as BSA 19-6508 but the 60-2133 entry says it's taper-thread, that - as I say - is just the general trade confusion over the part numbers. facepalm If you want an NPS switch for your '71 A65, order 60-3719 from the confused trade ...

Originally Posted by Allan G
would imagine there is just as much meat on an A65 as there is surrounding the threads on a triumph casing.
Mmmm ... I'm only familiar with the switch position on a '70-on single; if the A65's similar, much more "meat" than a Triumph timing cover.

[Linked Image from cdn.shopify.com]

... gives an idea of how little "meat" there is around a Triumph twin's OP switch hole ...

Hth.

Regards,

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I stand shocked and corrected by how little Meat the triumph cases have, I don’t consider the A65’s to be much nuts probably double that.

After I bought the incorrect switch I did some scouting and found some correct Smiths NOS NPS switches with same numbers etc as BSA supplied. I bought a couple and fitted one to a friends OIF.

I’ll try and find the service sheet that I have buried somewhere. I do most of my typing via my iPhone, whilst it works well it’s not great at converting Epserts of PDFs into images... it also has its own mind on spelling..... when I use the works tablet my spelling gets even worse laughing

I rightly or wrongly assume that most if not all fluid type switches would use the F type thread (though I’m certain I got my notes above from the service sheet) though if these switches are specifically made for the classic market and not the same as something that fits a Ford etc then god only
Knows what thread they used on the switch (hence the over sized ones you mention)

Got to add, I’m completely fed up with poor quality parts, and more so vendors that refuse to learn what they are selling. Even seeing the name
LF Harris no longer instills faith in the part being of decent quality. On some parts they give Wassel a good run for their money.


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Why not just run a NPS die over the NPT threads?

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Allan G Offline OP
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Originally Posted by DMadigan
Why not just run a NPS die over the NPT threads?

That wouldn’t gain me anything Dave, I have both types of switch, but only since post the event where the crankcase suffered the damage to the first 3/4 of the threads.

Looks like the only viable option is carefully cleaning up the threads within the crank case with the tap, and doing test fits with the switch.

I might try the PTFE method first, see if it is viable enough to crush the compression washer like that, if not then it’ll be the npt route.


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Ok, so I took some measurements and compared them with the specs I have seen for Npt online.

Online it says the major OD is 0.405” my switch measures 0.402 at this point.

Looking at the NPT and NPTF Taps I have, the major od on both of these are 0.410”.

M10 thread would be 0.395 or just under from what I can tell. But not looked properly at this as it would be more a back up choice.

The NPS Switch is close on 0.385-0.390, I didn’t pay much attention as I could tells it was quite a few thou smaller despite some sites saying the major OD for NPS was 0.405.

This I think is good news, it gives me confidence to crack on with the NPT switch that I have.


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Allan G Offline OP
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So...

I’ve tapped the case, the npt switch threads in nicely, the starting portion of the threads is smaller than the NPS switch so I will use the 542 sealer again when I fit it properly. The switch tightens up but I wanted to be sure that the switch is tightening up on the thread and not just on the flat face.
The A65 cases are recessed to support the crushable washer so you cannot tell easily. A drop of Stewart’s Micrometer blue and threaded the switch in was sufficient to tell me that it was only the threads it was tightening up on.

These new switches also have a Hex at the wider part of the switch so you have to be careful because the corners of the hex catch the body. (They must all be drilled slightly different as I have seen some fitted where you can slide a socket over without worry. Because of this I have ordered an extension piece just to strand the switch proud by a few mm.

Worth adding that the 542 had such a good grip on the NPS switch that I nearly left it fitted.


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I recently ordered a new switch from The Bonneville Shop. They listed both the early and late parts. I ordered 60-2133.
What I got was LF Harris, and has a straight thread and an O ring in place of the usual copper washer. As Allan pointed out, the switch has a large hex.
I put this on the Trident, using Teflon tape. I used the old switch from the Trident on my A65. I was pleased that it screwed in nicely, as the last thing in that hole was an NPT adapter for a gauge. I had never screwed that adapter in more than snug, so the threads survived.


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Hi David,

Originally Posted by DavidP
I recently ordered a new switch from The Bonneville Shop. They listed both the early and late parts. I ordered 60-2133.
What I got was LF Harris, and has a straight thread and an O ring in place of the usual copper washer.
Intriguing ... 60-2133 is the earlier of the two numbers the trade's used (60-3719's the other); the later number must be NPS; if 60-2133's also being supplied as NPS, what's being used for NPT? confused

Regards,

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Hi Allan,
Originally Posted by Allan G
M10 thread would be
Mmmm ... but it wouldn't be the right tpi - M10 is likely to be 1 mm. pitch, so 25.4 tpi, more coarse than either NP.

Originally Posted by Allan G
These new switches also have a Hex at the wider part of the switch so you have to be careful because the corners of the hex catch the body.
... Original switches have a length of 1/2" OD between thread and hex. ...

Regards,

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Hi Stuart,

This just reminded me
Originally Posted by Stuart
Hi David,

Originally Posted by DavidP
I recently ordered a new switch from The Bonneville Shop. They listed both the early and late parts. I ordered 60-2133.
What I got was LF Harris, and has a straight thread and an O ring in place of the usual copper washer.
Intriguing ... 60-2133 is the earlier of the two numbers the trade's used (60-3719's the other); the later number must be NPS; if 60-2133's also being supplied as NPS, what's being used for NPT? confused

Regards,

I saw a comment on Facebook yesterday, the question I don’t think was related to the switch but one of the many diverse answers was “I can see from here that the switch is taper thread”.

Now I don’t claim to have 20:20 vision, last time I had my eyes checked was when I was 18, but I consider myself to have decent eye sight I couldn’t see from 3 feet whether my switch was taper or not. I had to double check with the vernier, so how this chap could see on a poorly focused image is beyond me.... but that’s just diverting from this topic.


Originally Posted by Stuart
Hi Allan,
Originally Posted by Allan G
M10 thread would be
Mmmm ... but it wouldn't be the right tpi - M10 is likely to be 1 mm. pitch, so 25.4 tpi, more coarse than either NP.

I agree (though it would be hard not to) I noticed a comment by Rod on the Triumph forum saying that he had re-tapped to M10, which is why I brought it up... tbh if it works for him then well and good, but I really don’t like threading ptfe into aluminium to pack the switch in place by taking up the slack in the thread. Reason I say this is I had a similar situation with a 5/16 BSF bolt, it lasted about 6months on the oil feed before it started leaking, when I tried to take it apart at a branch camp it brought the case threads out with it and I ended up on the breakdown wagon. I helicoiled it to 5/16 UNC (which is what the factory did from 1969) and never had another issue. So you can see why I’m so keen to have a decent thread for the switch to thread in to.

Originally Posted by Allan G
These new switches also have a Hex at the wider part of the switch so you have to be careful because the corners of the hex catch the body.
... Original switches have a length of 1/2" OD between thread and hex. ...

Regards,[/quote]

Thankyou, I notice with the original nps switch that it stands further forward than the replacement style also because the hex is on the smaller section. The other option would be to round the corners of the switch and thin the hex down so the switch will fit better in the rubber boot and not be working against the crank case on the corners.


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68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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