Lotus Elan

1/4" NPTF Oil Gallery Plugs

PostPost by: rgh0 » Sat Apr 04, 2015 10:43 am

englishmaninwales wrote: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: )?


Brass will work fine and I have pulled them out of a few blocks, i am not sure what was originally fitted. However like you observe they do round off more easily than steel plugs so I always put steel plugs back

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PostPost by: ort » Sat Apr 04, 2015 11:35 am

the plugs are NPTF as I have stated in other posts I spent 25 years making the cutting tools for Ford and Lotus
oil plug.jpg and


I wouldn't use brass as it has a tendency to flake which will end up in the oil galleries, this is why you should never use a brass drift on bearings. I have come across factory fitted brass plugs usually with a screwdriver slot which are a right royal pain to remove

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PostPost by: rgh0 » Sat Apr 04, 2015 12:12 pm

Iain

An interesting old blueprint - I notice the Pinto reference on the drawing - was this drawing for American made blocks for the Pinto which would perhaps explain NPT use there?

i will get out my measuring tools again tomorrow and go over a few blocks again but it sure did not look like it was NPT when i measured them previously


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PostPost by: ort » Sat Apr 04, 2015 3:47 pm

Rohan
the blueprint covers all the 4cyl engines produced at Dagenham the plugs are common across the engine ranges.
as a side note the line transfer m/c's for the kent based engines were only pulled out in the late 90's.
the only bsp/bspt taps produced were for the tractor plant at Basildon and from memory I think they were discontinued in the early 60's.
NPTF or Dryseal does not require sealant to provide a gas tight seal as it is full metal to metal contact, if you look at a used plug you can see the damage to the thread crests where it has been in contact with the crests of the female thread. BSPT is not a gas tight seal and requires a sealant.

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PostPost by: englishmaninwales » Sat Apr 04, 2015 4:39 pm

Ah, so we're back to NPTF again :?
So why don't the NPTF replacements fit?
Quality?
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PostPost by: tonyr27 » Sat Apr 04, 2015 5:27 pm

Malcolm

I wonder if they have been replaced on a previous rebuild with BSP plugs, which may have slightly opened up the threads.

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PostPost by: englishmaninwales » Sat Apr 04, 2015 9:00 pm

Hi Tony
Yes maybe that's the reason. I'm getting a couple of 1/4 BSPT plugs after the weekend and then I can compare how they fit against these NPTF ones.

Missing your Caterham yet? I'm off to Loton Park Hillclimb tomorrow with mine, first time after a 2 year break from competition, so I'll be rusty and given it is the first event after the winter, it will be a touch slippery, despite nice new A24 Avon ZZRs :shock:
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PostPost by: tonyr27 » Sat Apr 04, 2015 10:56 pm

Hi Malcolm

Yes, I'm starting to miss the Caterham but enjoying learning about Elan's!

Good luck at Loton, hope it goes well and the weather is a little warmer for those new tyres.

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PostPost by: rgh0 » Sat Apr 04, 2015 11:58 pm

ort wrote:Rohan

NPTF or Dryseal does not require sealant to provide a gas tight seal as it is full metal to metal contact, if you look at a used plug you can see the damage to the thread crests where it has been in contact with the crests of the female thread. BSPT is not a gas tight seal and requires a sealant.

Iain


While i know that the design intent with NPTF threads was that they did not require a sealant I have 30 years experience of using them in practice in the petrochemical industry on small bore piping and instrument fittings that says you need a sealant !!!

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PostPost by: rgh0 » Sun Apr 05, 2015 4:11 am

Well I spent a happy hour or two in the garage measuring up plugs and ports and i was wrong about having BSP plugs and ports and Iain is correct :oops: :oops: :oops:

I discovered I had a mix of NPT and BSP plugs. When I sorted out and measured them carefully I found the plugs that looked original from engine blocks i had dismantled were all NPT in both the 1/4 and 1/8 sizes.

The ports in the engine blocks also look like they are NPT based on how the plugs thread in. Not possible to measure the inside thread pitch directly and the port diameters are identical for NPT and BSP so you cant tell by that either I discover. So how the plugs thread in is the only way to tell.

All the original 1/4 NPT plugs were around 9mm long and screwed in about 5 threads or 7mm to be about 2 mm above the surface before locking up on the taper. The 1/4 BSP plugs screwed in about the same distance until what felt like the threads jammed rather than the taper locking up

The 1/8 NPT plugs screwed in about 5 threads until the taper locked up, The 1/8 BSP plugs felt looser in the hole and screwed in about 8 threads until the taper locked up.

My conclusion is the threads in the block are NPT. You can screw BSP plugs into them in practice and get them to seal OK with appropriate thread sealant but you should use NPT. Incidently the water jacket drain tap or plug is also 1/4 NPT not BSP.

The people who decided to make NPT just slightly different from BSP sure created a challenge in identification.

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PostPost by: Lyn7 » Sun Apr 05, 2015 7:15 am

Hi Guys, quite a thread! I agree completely with Rohan's findings. I have worked on a number of twin cam blocks and cross flow and all the gallery plugs have been NPT. I am currently building a 100E Ford block for an OHIV conversion. The engine number indicates it is a late 1958 build date and the gallery plug (only one) is NPT.
Regards Lyn...
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PostPost by: promotor » Sun Apr 05, 2015 7:57 am

englishmaninwales wrote:Ah, so we're back to NPTF again :?
So why don't the NPTF replacements fit?
Quality?


They don't fit because Burton don't know what they are doing (and when you raise a concern with them regarding this very issue as I have they don't care). Profit over quality.

Go to an air line product company and ask for some industrial type ones. That's what I did when I needed replacements.

And as with a lot of stuff nowadays (from a number of vendors) I simply replace with used good condition genuine parts rather than new because original Ford parts are still amazing in comparison. I nearly always re-use Ford gallery plugs and have never had an issue.
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PostPost by: ericbushby » Sun Apr 05, 2015 8:29 am

Well, there you go, I was wrong again.
With Iain's background knowledge and Rohan' s hands on research we appear to have a result.
This is an excellent example of what this forum is good at.
A problem often occurs with suppliers employees not having sufficient experience and knowledge to know the difference between similar looking fittings or not knowing how to measure them.
How could they as they are not as old as some of us, well me anyway.
Let us know how you get on Malcolm.
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PostPost by: RichardHawkins » Sun Apr 05, 2015 4:14 pm

Malcolm,

I am reluctant to comment, as what Rohan says is usually correct, especially the bit about the threads being similar and you not noticing the difference of one thread per inch on a plug that is probably only 3/8" long. However, although our engines were built in Britain the ownership of the company was Ford of America. At this time the British motor industy particularly Ford was using American thread systems, which is why we have UNC & UNF threads all over our vehicles. I thought the plugs you refer to were National Pipe Thread Taper. Of course I could be wrong, and with Lotus I often am, so check carefully, and if you do not have any, buy some thread gauges, and a reference booklet, so that you can drive yourself half crazy trying to tell the difference between similar threads.

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PostPost by: englishmaninwales » Sun Apr 05, 2015 8:54 pm

I'm very grateful to all the contributors on this thread, especially to Iain for the background information on the correct specification of the oil gallery plug and posting on here the Ford blueprint, also to Rohan for the time spent in his garage on Easter Sunday looking at oil gallery threads (when he could have been sitting beside the pool in his Melbourne garden with some tinnys in the esky!).
I've learnt a bit about tapered pipe threads too :D
I shall update the thread once I've had a chance to order some more plugs from a different supplier.
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