Lotus Elan

1/4" NPTF Oil Gallery Plugs

PostPost by: englishmaninwales » Fri Apr 03, 2015 7:54 pm

I bought 2 replacements, but find that they screw in too far, well below the surface of the block and partially block the oil feeds to No1 and No5 main bearings. Much worse at the rear than the front.

The threads in the block seem ok as far as I can see.

The replacements I got are 10mm long (about 2mm longer than the originals). This extra length doesn't seem to be the problem, rather they seem to screw in too far. The one original has gone back in as per normal (on the oil pump side half gallery) with about 2mm proud of the block.

Done a search on here, but the only the solutions to this I could find were:
1. Tighten up with PTFE tape - Not keen on tape near oil supplies
2. Shorten the plug - I think this will break into the hex key way as 7.3mm deep

I don't know much about pipe threads, but is it possible to get oversize NPTF?

Thanks
Malcolm
Last edited by englishmaninwales on Tue Apr 07, 2015 11:35 pm, edited 1 time in total.
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PostPost by: Lyn7 » Fri Apr 03, 2015 8:28 pm

Hi Malcolm, some pipe thread types are tapered, but I cannot speak for yours? Maybe you could purchase alternative plugs from another supplier. You could try an on line search as you know what to look for.
Good luck Lyn...
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PostPost by: ericbushby » Fri Apr 03, 2015 8:31 pm

I wonder if the original plug is BSP, british standard pipe thread, not NPT, national pipe thread, which I believe to be american. These threads are similar but different. A british engine will have had common british threads.
I had worked in engineering for many years before I even heard of NPT. That was only when my employers started exporting to the states. We certainly had never heard of it in the 60's and would have had trouble sourcing fittings.
A local plumbers merchant should stock BSP plugs.
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PostPost by: prezoom » Fri Apr 03, 2015 8:34 pm

I've seen tapered pipe threads tightened up by cleaning the plug very well in the thread area and then applying a light coat of solder to the threads. The solder will deform when threaded in, but will also provide a good seal.
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PostPost by: ort » Fri Apr 03, 2015 8:51 pm

Eric
the threads are NPTF not BSPT
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PostPost by: ericbushby » Fri Apr 03, 2015 8:58 pm

Iain,
OK, I am surprised and now better informed. Thankyou.
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PostPost by: AHM » Fri Apr 03, 2015 10:01 pm

Eric,

I believe you are correct - The oil and water tapings are either BSP or BSPT.

Of course if you try putting an NPT fitting in it will lock-up because it is 27 tpi rather than 28 tpi.(edit - wrong size! Should be 18 / 19 tpi)
Last edited by AHM on Sat Apr 04, 2015 1:19 am, edited 1 time in total.
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PostPost by: englishmaninwales » Fri Apr 03, 2015 10:38 pm

The plug at the cross drilling on the RHS engine mount is BSP.
I wonder if it is of poor quality with insufficient taper, it feels that way when tightening it up. Measuring there is approx. 0.1mm difference over its 10mm length.

I'll try some different suppliers.
Last edited by englishmaninwales on Tue Apr 07, 2015 11:38 pm, edited 1 time in total.
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PostPost by: AHM » Fri Apr 03, 2015 10:50 pm

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PostPost by: ericbushby » Fri Apr 03, 2015 11:22 pm

AHM
Thankyou, but that's nonsense, I am never right, ask the wife.
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PostPost by: rgh0 » Sat Apr 04, 2015 12:44 am

Later Edit ::What i wrote below is wrong !!!! - see later post for correction :oops: :oops: :oops:


Dont know why Burtons say NPT oil gallery plugs? All my plugs are 1/4 BSPT for the oil galleries in my blocks which are 1/4 BSPT.

The NPT plugs will be slightly smaller in diameter than equivalent BSP and thus go in to far as you observe. The 18 TPI for NPT versus 19 TPI for BSP will probably not be noticed when fitting together given the smaller diameter and short length of engagement.

Cheers
Rohan
Last edited by rgh0 on Sun Apr 05, 2015 3:34 am, edited 1 time in total.
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PostPost by: AHM » Sat Apr 04, 2015 1:14 am

Eric,
I've never come across, nor had cause to use NPT. I hadn't even heard of the more obscure NPTF. Even in Japan, where NPT is common they use BSPT on engines. I can't fathom why a UK manufacturer would switch between everyday BSPT and an obscure American thread on the same engine, let alone machining station..... But that doesn't mean we are right!

Malcolm,

You can walk into somewhere like toolstation or screwfix and get a BSPT fitting. Ask for NPT and they will give you a blank look.

The Burton fittings don't appear to be very tapered. Have you held one up against the good one to see if the threads match?
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PostPost by: englishmaninwales » Sat Apr 04, 2015 7:07 am

Well that would seem to be the explaination :D
I'll get some 1/4 BSPT plugs.

I thought the taper looked minimal on the NPTF ( measures 0.1mm) after I discovered the problem. I'm reluctant to remove the one original to compare as I installed that first and there will be thread lock debris left if I remove. The new ones I trial fitted dry, that's how I found the problem.

Great forum, thanks.
Malcolm
Last edited by englishmaninwales on Tue Apr 07, 2015 11:39 pm, edited 1 time in total.
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PostPost by: englishmaninwales » Sat Apr 04, 2015 8:08 am

Any reason why I shouldn't use brass 1/4 BSPT plugs (other than getting them out at next rebuild - probably not my problem :lol: )?
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PostPost by: AHM » Sat Apr 04, 2015 9:17 am

I would prefer brass but they may be a few pence more expensive. Usually depends what is available for flush fitting hex drive etc

If you don't want to take the other one out you could try a known bolt as a thread gauge.
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