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I know this subject has been raised before but my question has a slightly different angle. The correct thread is 1/8"NPS, but fittings with this thread are proving very hard to find (Demon Tweeks, for example, had never heard of NPS, only NPT, in over 30 years of trading). The reason I'm interested in this is because I'm fitting oil pressure gauges to my project bikes.

The Morgo website offers fittings which are 1/8 BSP. I presume that if anyone buys one of Morgo's oil pressure gauge kits, they come with a BSP fitting. I understand that BSP of this diameter is 28TPI, whereas NPS is 27TPI, but you can cram a BSP fitting into the T140 timing cover successfully(?). If using BSP fittings as a substitute is not the bodge it sounds like to me, that's fine, I'll buy fittings from Morgo. However, if this is the bodge it sounds like, I would prefer to find proper NPS fittings if I can. Can anyone gve a well informed opinion? And if using BSP in NPS is seriously frowned upon, can anyone recommend a retailer that sells NPS right-angle fittings? Thanks.


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Hi; I am interested too due to I have an oil gauge and and the light. PO put it on the external oil filter but I will remove that and put it on the cover.
I do not know what thread is the gauge tube etc.

Thanks

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How about an 1/8 NPS banjo bolt? If you want to run a gauge then it should be with braided hose.
Presume you mean BSPP (parallel pipe)? If Morgo is using tapered pipe fittings you COULD do it but it will expand out the thread and then fitting a BSPP will be loose. In either case the pitch is wrong, an original Smiths switch PS 5300/07 is 27 TPI.

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Hi, While it’s possible to screw BSPP 1/4-28 onto the late timing cover, it doesn’t take torque properly without bending the threads. Don’t do it!! I have personally tried.

You are most correct it is very hard to locate 1/4-27 NPS. Many sellers say they have it. But when part arrives, it’s in fact tapered.

I finally gave up & bought tap & die. Made my own fittings. But…. If you make it to nominal diameter, it will bee too tight & not screw in. So you want to measure OD of a proper fitting oil pressure switch & make the OD of your blank the same.

This thread was a bad idea from a replacement parts standpoint.

It is very common thread in lamp parts, like the threaded tin the bulb socket screws onto. But for hydraulics it’s hard to come by in the configurations that are useful to us.

Good luck on your search.
Don


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It's not surprising to find obsolete threads on obscure things like that. I discovered the 2BA threads in the Lucas taillight are still used for dart heads. Not that a dart tail in a taillight housing would be useful. I have seen brass fittings with lamp threads, though.

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As a side note I bought one of these as they were recommended over on the TriumphRat forum.

https://www.ebay.co.uk/itm/275219256985

Be warned that It was uncomfortably tight right from the get go. it measured 0.2 or 0.3 mm greater OD that my original switch (9.9mm vs 9.6mm) if memory serves.

I happened to have an old 1/8 27 NPT tap that I run the new switch through, it took off just a bit, and now it screws in correctly.


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Ever so naughty, but I have run a die down a thread, in my case to convert for the 26tpi cycle thread of a pre-unit cover.

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1/8 nps is the same as 1/8 ip... or 1/8 ips .
( they are both parallel sided , not tapered 27 tpI )

nps > national pipe straight
IP .>.Iron Pipe
IPS iron pipe straight

straight threads are not sealing threads , a gasket or o-ring provides the seal and the threads compress the seal

IP is an American thread standard , allowing interchangeability
for lighting fixtures , from about 1900 .
As an obscure thread
it lives with most of us in our homes without our even knowing it
taps and dies for 1/8 ip are available ( because wall lights , lamps and chandeliers are still being made)
and short lengths 1/8 ip pipe are available at almost every local North American hardware store .
( I don't know about Europe or UK )

[Linked Image from cdn.shopify.com]

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Definitely keeping that chart. Thanks. quinten.

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I will give Morgo a ring n Monday and ask them why they're selling BSP fittings when they are not correct for the application, unless they claim they interchange perfectly.


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Hi, Problem is with the lighting threads.... They don't make any fittings we have a use for. They don't even make a straight plug that we could put sealing washer on if you wanted to remove OP switch & not use one.

Straight pipe threads are still in use in industry but they don't make fittings that we need. Like 1/8-27 straight to 1/8 taper, or metric. Or an banjo bolt. The oil pressure gauge sellers have them made somewhere, but where? Will they sell them separately?

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Originally Posted by Tigernuts
I will give Morgo a ring n Monday and ask them why they're selling BSP fittings when they are not correct for the application, unless they claim they interchange perfectly.

Morgo are selling an adaptor to fit the very common 1/8” BSP oil light switch and/or 1/8” BSP pipe union (for a gauge), to pre-1968 timing covers.

There’s one on my bike and it works.

What are Morgo doing wrong, that you’re going to phone them about?


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Hi, Morgo sells 1/8-27 NPS banjo bolts & banjo. The NPS straight has 2 rings machined in just above threads. There gauge hose adaptor I think is BSPS.

Here's the page I'm looking at. It certainly is confusing.

https://www.morgo.co.uk/product/multi-point-pressure-adaptor-kit/


Morgo doesn't seem to mention the oil tube fittings are 1/8 BSP (taper). That's why some many options of banjos are 1/8 BSP female. They seem to not make plain exactly what you need to fit gauge. So you can use pressure switch also. If not you must fill space on banjo bolt with blank banjo.

Maybe Morgo is not best kit for your use. Others make kit with adaptor that is just an adaptor. No pressure switch will be used, just the gauge only. Again, very carefully verify the thread on kit is correct for your timing cover. The kit sold in this link comes with both adaptors.

https://www.classicbritishspares.co...581&_ss=r&variant=32118525755494

Don


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Thanks Don, I've had a look at the CBS page but it seems their adaptors are either 24TPI or 26TPI. 1/8 NPS is 27TPI, so I don't know what's going on there.


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Originally Posted by triton thrasher
Originally Posted by Tigernuts
I will give Morgo a ring n Monday and ask them why they're selling BSP fittings when they are not correct for the application, unless they claim they interchange perfectly.

Morgo are selling an adaptor to fit the very common 1/8” BSP oil light switch and/or 1/8” BSP pipe union (for a gauge), to pre-1968 timing covers.

There’s one on my bike and it works.

What are Morgo doing wrong, that you’re going to phone them about?

Thanks for checking up on me again TT, very helpful indeed. My point was clearly made above but as you found it confusing I'll try to explain more simply:

The T140 timing cover has a thread for a 1/8" NPS oil pressure wanring light switch. Therefore, to fit an oil pressure gauge the correct fitting is also 1/8" NPS. Morgo are offering 1/8" BSP adaptors. These are not correct for the NPS threaded timing covers. I am going to phone Morgo and ask whether they can supply NPS adaptors or whether they find that the BSP adaptors fit the NPS threads satisfactorily. Is that OK with you, or do you want to tell me why I shouldn't?


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Originally Posted by Tigernuts
Thanks for checking up on me again TT, very helpful indeed. My point was clearly made above but as you found it confusing I'll try to explain more simply:

The T140 timing cover has a thread for a 1/8" NPS oil pressure wanring light switch. Therefore, to fit an oil pressure gauge the correct fitting is also 1/8" NPS. Morgo are offering 1/8" BSP adaptors. These are not correct for the NPS threaded timing covers. I am going to phone Morgo and ask whether they can supply NPS adaptors or whether they find that the BSP adaptors fit the NPS threads satisfactorily. Is that OK with you, or do you want to tell me why I shouldn't?

Everything’s ok with me. Their adaptor is 3/8” Cycle thread, to fit a pre-1968 cover, so a pre-1968 bike can have an oil light.

It looks like TR7RVMAN’s long Morgo adaptor might allow a 1/8” BSP to be used with an NPS timing cover, but it’s a big clumsy thing.

[Linked Image from morgo.co.uk]


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The Morgo multi-adaptors are a mess! I'll try asking LP Williams, as they sell oil pressure gauges. Hard to believe such a straightforward thing should be so complicated!


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That morgo thing is certainly ugly, though I did see both fittings and the bolt are available in NPS, though they don't specify thread count.

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The answer must be to use an NPS die on a switch with different thread, or do it in a lathe.


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That Heath Robinson style collection of fittings on Morgo's site includes what must be a 1/8" NPS banjo bolt. I will see if they'll sell me a couple of them, then see about getting a hose fitting with suitable size female banjo. Having said that, if it's that simple, why aren't Morgo doing that? I hope to find out on Monday.


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Hi Taps & dies are easy to come by.

But you can’t turn a 26 tip into a 27.

You can run straight for over 27 tapered, but the metal is still tapered.

Don’t use thread chart when making fittings. That’s what I did. The Triumuph straight oil pressure switch thread major diameter is smaller than standard. You make it standard major diameter it won’t screw on. Too fat.
Don


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Too bad that 1/8 NPS die is not adjustable.
If there were demand, fitting like this Radium could be made to fit Brit bikes.
[Linked Image from cdn.shopify.com]

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Hi, Does anyone have an original Lucas straight thread pressure switch that can measure Major (outside) diameter of threads?

I want real life original switch measurement. Not out of a book or chart.
Thanks, Don


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By chance I was looking through my taps and came across a 1/8 NPS 27 tap. Must be rare!


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