Oil Pressure Switch

[daveejhitchins]

I'm doing a comprehensive refurb on my 'Ruby' Traveller - But more of that in another thread . . .

I recently pulled the oil pressure switch ready to fit a replacement. The old switch had a tapered thread which didn't go into the block very far. This seems to have left the deeper threads blocked e.g. I can't fit the new switch fully home.

Would anybody have the size and thread details for the switch, please? I'll need to obtain a tap to clean out the block. Yes, I know this may drop swarf into the sump - OK, as I still have to clean-out the sump - I'll also be fitting a magnetic sump plug before firing her-up.

Thanks - Dave H.

[philthehill]

The oil pressure switch has a taper male thread and will not go fully into the block. The threads in the block are 1/8" National Pipe Thread(NPT) and are parallel. The taper oil switch threads will never go fully home into the block.
Just fit the oil pressure switch and gently tighten until it will tighten no more and that is the switch fitted.
There is no need for a tap.
Any swarf generated will not drop straight into the sump - it will travel right around the oil galleries damaging all bearing surfaces.
I would recommend that the oil pressure switch threads are coated in Loctite 'Loc & Seal'. There is absolutely no need for PTFE tape.

[oliver90owner]

In addition to PTH’s posting, what makes do you think any/all metal swarf would simply end up in the sump, rather than potentially through a bearing?

[daveejhitchins]

The oil pressure switch has a taper male thread and will not go fully into the block. The threads in the block are 1/8" National Pipe Thread(NPT) and are parallel. The taper oil switch threads will never go fully home into the block.
Yes, I realise both your points, however, the OD of the threaded section only varies by 0.15mm and doesn't seem to tighten-up like the part I removed - which only screwed-in about half the thread length and was 'very' tight!

Just fit the oil pressure switch and gently tighten until it will tighten no more and that is the switch fitted.
As above it's not tightening fully - It's like I could carry-on until it breaks! Maybe a replacement is in order - they're only a fiver and I've spent more time on this than I should have . . .

There is no need for a tap.
Any swarf generated will not drop straight into the sump - it will travel right around the oil galleries damaging all bearing surfaces.
I would recommend that the oil pressure switch threads are coated in Loctite 'Loc & Seal'. There is absolutely no need for PTFE tape.
As mentioned I still have to remove the sump and clean-out the bottom end. So It won't be running any time soon.

Thanks for the replies - any other thoughts?

Dave ~H.

[philthehill]

I have just checked several oil pressure switches in a 948cc block. They all go in just sufficient to cover half the threads of the oil pressure switch. That equates to about 8mm. Because of the taper thread the more you screw the oil pressure switch in the tighter it becomes and that is how the thread is sealed.
The oil gallery behind the oil pressure switch does not drain into the sump. The oil in the gallery goes to all the bearings before it goes back to the sump. Cleaning the sump whilst an overall benefit to the engine does not remove any swarf/crud from the oil galleries so no real benefit. Only with the oil pump turning does oil move around the engine oil galleries.
You can help catch the swarf/crud by greasing the tap. The grease traps the swarf/crud which can then be removed with the tap.

[daveejhitchins]

I have just checked several oil pressure switches in a 948cc block. They all go in just sufficient to cover half the threads of the oil pressure switch. That equates to about 8mm. Because of the taper thread the more you screw the oil pressure switch in the tighter it becomes and that is how the thread is sealed.
My switch goes in, relatively easy, to the last 2mm of thread (a few more turns it would tighten-up to the washer) before I get that "it's going to break" feeling. I'll get back with the results of a replacement . . .

The oil gallery behind the oil pressure switch does not drain into the sump. The oil in the gallery goes to all the bearings before it goes back to the sump. Cleaning the sump whilst an overall benefit to the engine does not remove any swarf/crud from the oil galleries so no real benefit. Only with the oil pump turning does oil move around the engine oil galleries.

Of course it does . . . It is 50 years since my last encounter with an A series. Hopefully the replacement switch will tighten-up so the swarf issue will go away . . .

You help catch the swarf/crud by greasing the tap. The grease traps the swarf/crud which can then be removed with the tap.
Yes, I've used that method before . . .

Dave H.

[philthehill]

What washer? There is no requirement for a washer - the taper threads are self sealing.
If the switch was supplied with a washer you have the wrong switch.
Below can be seen the amount of thread exposed on the oil pressure switch and that is correct.

Gauge feed 1.JPG (1.37 MiB) Viewed 3090 times

[daveejhitchins]

My switch is totally different - see photo (not mine but similar!) The threaded section extends to the body . . . And, it screws-in leaving the washer 'just' loose.

Oil Pressure Switch.jpg (14.09 KiB) Viewed 3070 times

Dave H.

[philthehill]

Many thanks for the photo of the oil pressure switch.
The switch is non standard and that is why you are having problems fitting it.
I would suggest that the threads of the switch are bottoming out.
The correct 'plug' (parallel) tap inserted into the oil switch aperture bottoms out at 7mm depth.
I would also suggest that the correct switch which has a taper thread is obtained and fitted.

[myoldjalopy]

The OP's picture of the switch looks very similar to the one available from ESM: https://www.morrisminorspares.com/engin ... cc-p830270
I fitted one of these from ESM recently and it fitted fine (although it did not have the washer). I noticed the old one I removed had the shoulder (like in Phil's photo) but the new one didn't. Nevertheless, it must have had the taper thread as it screwed in fine and works as it should....

[daveejhitchins]

New switch on order . . . Dave H.

[philthehill]

myoldjalopy
The ESM switch in your link has a taper thread whereas the OPs switch has a parallel thread.
The parallel thread has no sealing qualities and that is why a washer must be used.
Phil

[daveejhitchins]

New switch arrived - fitted perfectly

Dave H.

[geoberni]

What washer? There is no requirement for a washer - the taper threads are self sealing.

Phil
I'm a few months late catching up on this, but I found your comment interesting about having a washer, or not.
I've just noticed that the original Parts Catalogue, AKD 3541, shows a Copper Washer.....

pressure switch.JPG (10.83 KiB) Viewed 2798 times

[philthehill]

As I mentioned above - if the original oil pressure switch has a parallel thread then it will require a washer. Parallel threads have no sealing qualities.

[geoberni]

As I mentioned above - if the original oil pressure switch has a parallel thread then it will require a washer. Parallel threads have no sealing qualities.

So the original was a parallel thread.

[daveejhitchins]

Hmmmmm! So, If anyone is looking for an original (?) I have one

Dave H.