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Oil pressure gauge adapter


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What thread/size is in the block on a 1600 x flow?

I've got a pressure sensor which I think has a 1/4 ntp male thread but it seems too big to fit in the block. It's not massively big, just a mm or so.

I've tried a 1/8 ntp fitting but this is far too small.

Are there any other thread sizes?

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i removed a junky repro oil pressure pipe from a crossflow recently, and because the pipe had modern fittings, it had been supplied with specially made adaptors both ends to mate it to the original block and clocks, but in usual repro crap style, the dash had to be ground out to fit it

cant beat the original parts

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6 hours ago, Miniliteman said:

All 70's XFlow blocks have 1/4 NPT thread. Maybe the sensor you have is metric M14. (VDO has M14 x 1.5 sensors)

Thanks for the confirmation. I'll order something with 1/4 ntp thread which I hope will fit ok.

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Update: I ordered another oil adaptor but still having problems fitting it. The attached photos show the old adaptor, the new one and the old sensor.

The new adaptor won't screw into the block as it seems too big. If I measure the thread in the block with callipers it's 11mm. The thread on the new adaptor is 13mm. I know I'm measuring the major diameter on the adaptor and the minor diameter in the block but a 2mm difference seems a lot. 

I also understand that the thread is tapered so the dimensions will be slightly different along the length of the thread.

As you can see in the photo the thread on the old adaptor has been badly damaged so there was obviously a problem when this was fitted previously.

Strangely the sensor will screw nicely into the old adaptor but will only go two turns in the new adaptor before it comes to a stop. I'm reluctant to force it as the thread in the aluminium adaptor will easily be damaged. The sensor will not screw directly into the block.

I've checked the thread in the block by running a pick along the thread and it appears to be undamaged.

All this keeps me thinking that the thread in the block is slightly different to the adaptors but it's very close. The block is definitely not 1/8 ntp as that is far too small.

I'm at a loss so has anyone got any suggestions?

 

IMG_20240709_115202938_HDR.jpg

IMG_20240709_115210573_HDR.jpg

IMG_20240709_115213210.jpg

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18 hours ago, Miniliteman said:

Looking at the damaged thread of the old adaptor me thinks that some of that damaged thread is stuck into the thread of the block.

I've checked that and it's all clear 🤔

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just a few thoughts, nothing definite, just a few thoughts, so don't shoot the messenger

my block and correct original union match your 11mm and 13mm

even in the pictures, the pressure switch looks too big

Aluminium threads have a habit of picking up, mainly when undoing, especially if the threads are dry, causing that sort of damage

that aluminium fitting, firstly are you sure its 1/4 NPT, 1/4 BSP is very close, but different, ive just checked 2 taps together to make sure, and also tried putting a 1/4 BSP in the hole in a block and appears marginally too big, whereas the NPT tap fits, the thread pitches are marginally different, but the BSP made in aluminium, could probably be forced in and cause that damage

the block is a straight 1/4 NPT designed to have a STEEL fitting of 1/4 NPT tapered so its threads seal, not a crappy soft aluminium piece, when using the pressure gauge

not had to fit a switch, only removed them tbh, but looking at your picture, that looks like a straighter thread and would use a sealing washer to seal it, but as said, it does look too big

the aluminium block also looks as though its possibly been overtightened, possibly to get the tee off in the right place, which again could cause that degree of damage, and if so, ur lucky it didnt snap in there

it would worry me as to how much debris (if any) has entered the engine 

if your insistent on wanting both pressure gauge and pressure switch, i would get that block manufactured with the correct required threads in steel, and the same with that brass fitting, better off in steel imho

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2 hours ago, Ray said:

just a few thoughts, nothing definite, just a few thoughts, so don't shoot the messenger

my block and correct original union match your 11mm and 13mm

even in the pictures, the pressure switch looks too big

Aluminium threads have a habit of picking up, mainly when undoing, especially if the threads are dry, causing that sort of damage

that aluminium fitting, firstly are you sure its 1/4 NPT, 1/4 BSP is very close, but different, ive just checked 2 taps together to make sure, and also tried putting a 1/4 BSP in the hole in a block and appears marginally too big, whereas the NPT tap fits, the thread pitches are marginally different, but the BSP made in aluminium, could probably be forced in and cause that damage

the block is a straight 1/4 NPT designed to have a STEEL fitting of 1/4 NPT tapered so its threads seal, not a crappy soft aluminium piece, when using the pressure gauge

not had to fit a switch, only removed them tbh, but looking at your picture, that looks like a straighter thread and would use a sealing washer to seal it, but as said, it does look too big

the aluminium block also looks as though its possibly been overtightened, possibly to get the tee off in the right place, which again could cause that degree of damage, and if so, ur lucky it didnt snap in there

it would worry me as to how much debris (if any) has entered the engine 

if your insistent on wanting both pressure gauge and pressure switch, i would get that block manufactured with the correct required threads in steel, and the same with that brass fitting, better off in steel imho

Don't worry, I'd never shoot the messenger. I'm always open to all suggestions or opinions and never assume anything. You have in fact raised some very interesting ideas.

The aluminium adaptor was very hard to get out so I'm not sure whether it got damaged going in or coming out. I did check straightaway in the engine block for debris and didn't see anything although I do share your concern that some may have found it's way into the engine. I will consider changing the oil.

I can only assume that the thread on the adaptor is NPT as that what the eBay listing stated. Unfortunately I don't have any taps to check. All the adaptors I see on eBay and elsewhere state NPT so I can't see that the supplier got this wrong.

I'll do a bit of research for another adaptor unless anyone can suggest a good quality one?

Thanks again for your post 👍

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i have a set of thread restorers, ill try the unf one in a block later, but tbh i think the threads in my spare blocks, are way too course for it to be unf, and i matched my union to the NPT tap earlier

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3 hours ago, Miniliteman said:

Then it might be that the thread is 1/2" UNF. Get a 1/2" UNF bolt and see if it fits into the block / adapter.

https://www.merlinmotorsport.co.uk/p/oil-pressure-gauge-t-piece-1-2unf-tp-1-2unf

I don't think it's a UNF thread. I've tried a 1/2" UNF tap which doesn't fit nicely. I've tried to take a photo which I think shows that the thread in the engine block is courser than UNF.

IMG_20240710_165503908_HDR.jpg

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Compared an M12 bolt, a 1/2" UNF bolt, a 1/2" UNC bolt and an oilpressureswitch with 1/4 NPT thread. Plus from all the above (measurements and photos) me thinks the block has had a NPT helicoil. If you fit one and the hole it goes into is a bit too small the helicoil will adapt to the hole and becomes a 1/4 NPT - (minus) thread. Fit an alloy (or soft metal) adapter into such a hole will deform the thread on the adapter. Check if it is a helicoil, if it is, take it out, rebore to proper diameter and fit a new 1/4 NPT helicoil.

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13 minutes ago, Miniliteman said:

Compared an M12 bolt, a 1/2" UNF bolt, a 1/2" UNC bolt and an oilpressureswitch with 1/4 NPT thread. Plus from all the above (measurements and photos) me thinks the block has had a NPT helicoil. If you fit one and the hole it goes into is a bit too small the helicoil will adapt to the hole and becomes a 1/4 NPT - (minus) thread. Fit an alloy (or soft metal) adapter into such a hole will deform the thread on the adapter. Check if it is a helicoil, if it is, take it out, rebore to proper diameter and fit a new 1/4 NPT helicoil.

Do you think that in the past someone has put the aluminium adaptor in and that's why the thread is so damaged?

How do I check that it's a helicoil?

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Just as an update I decided that I needed to get the car back on the road before I miss anymore of summer such as it's been this year!

I decided to put the old adaptor back so with some careful filling and cutting I managed to make use of the bit of thread that was undamaged. I carefully screwed it back into the block, it was fairly tight and I got about two full turns. Being aluminium it has probably damaged what thread remains but I used a bit of thread sealer to prempt any potential leaks. This also meant that the existing electric sensor could be reused.

I'm leaving it 24 hours before testing to let the thread sealer to 'go off' although the one I used doesn't harden.

Once we get to the winter I can spend a bit more time getting it sorted.

Thanks everyone for your input and suggestions, always good to get ideas to help progress a situation.

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