Oil pressure relief valve

[k. rogers]

Would someone know if the piston and spring inside a vintage pressure relief valve is interchangeable with the pre-war variety, or where I might obtain such a thing. Obviously, I will try club spares next Monday, but would be useful to know from someone more informed in the meantime. My vintage has an adjustable relief valve fitted, but with no insert it is running at a ridiculously high pressure, ie 50lb plus.

[k. rogers]

I know I am replying to my own question, but it has just occurred to me that if there isn't a piston inside the valve then I would be getting no or low oil pressure! Perhaps I will dig around in case it is stuck closed.

[ian Howell]

The oil pressure relief valve on my 1930 Long Four was a bit sloppy so I turned up a new piston that was a better fit in the valve body. I reused the originl spring.

Point to note: - There are a couple of TINY holes in the sides of the piston near the closed end. I think these may be to avoid 'hydraulic locking' of the piston in the open position.

I will be interested to see what effrect releasing the piston in your engine has on oil pressures at 'cold' and 'hot' states.

[Tony Fearn]

Hi Ken.
Search 7HP oil feed in Pre-war.
I did a sketch on Dec 18 2014.
Mr. Box may have what you want. Give him a ring.
Tony.

[k. rogers]

Thanks Tony, I did in fact see your diagram, however, mine is different from the pre-war type, though obviously works in the same way. I am hoping I will find the piston and spring stuck inside - I will post my findings.

[k. rogers]

I've had the (what I thought was) the pressure release valve off from the rear of the engine and there is no piston and spring!! Yet there is an adjustable bolt on the end with a lock nut. Is it possible there is a PRV somewhere else in the oil system? Surely if there isn't one present there would be very low pressure? Any ideas, anybody?

[ian Howell]

Thinks: -

IF there IS a reading on the pressure gauge, and

IF the gauge is connected via a pipe to the relief valve body, and

IF there are no piston or spring in place,

THEN possibly the outlet from the valve housing has been blocked off, either by not having a hole in the gasket or possibly by some sort of plug in the passageway through the crankcase.

Lots of IFs but the truth must surely lie somewhere there?

[k. rogers]

There was a lot of crud in the valve body which I have now cleaned out - I might be in for a shock when I start the car again ie low pressure!

[ian Howell]

With crud cleaned out there could be a couple of outcomes:-

1/ Low oil pressure due to the absence of the piston/spring. They should regulate the maximum pressure but this may be higher when the engine/oil is cold.

2/ High oil pressure due to blockages further along the oilways.

Either way, as long as you have plenty of oil in the sump there should not be too much - if any - damage to bearings etc. as long as oil is reaching the parts . (etc).

The Jowett manual suggests in the event of oil pump failure, overfill the sump and rely on 'splash' lubrication (and gentle driving) to get you home.

[k. rogers]

Unfortunately, because I have removed the distributor and dynamo to replace the drive gear I can't start the car at the moment, but after cleaning out the oil ways I am now getting about 15psi turning over by the starter as opposed to the 25-30psi I was getting before. The worry is how little pressure I might get when the engine is hot. I need to source a suitable piston and spring, but that could be difficult without knowing which car the valve came from originally. The 'thirties Jowett type plunger is too big a diameter, so I might have to get one machined down. The valve body has 'WADE' impressed on it which I should imagine means from the Stanley Wade engineering works after a bit of internet research.

[k. rogers]

The car is now running again after sourcing the correct dynamo drive gear from club spares. I am getting 20 -25 pounds pressure with the engine warm - I have yet to give it a run to get the oil really hot, but I am quite confident the readings will be adequate, considering it still doesn't have the piston in the PRV.

[k. rogers]

Just an update - I took the car to a rally yesterday, a very warm day, and she's running at around 25lb pressure going down to 5lbs on idle, so I don't think I need to worry too much about not having the piston and spring in the PRV body.

[ian Howell]

This is really weird! With no piston in the relief valve body obviously there should e no pressure - but \Hey!

As long as oil is reaching the bearings - as it presumably is or else you would not be a happy bunny - the mystery will eventually solve itself.

Since my car has only about 10psi when running 'warm' I will surely have to sort out the bearings soon - but not too soon I hope!

My concern/curiosity, is that starting 'cold' the oil pressure is way up, around 40psi, even with the relief valve set to as near 26psi as I could manage.

I suppose this could indicate congested oil ways but then the 'warm' pressure would surely be higher too?

Wouldn't it?

[Keith Clements]

Depends if you are using a multi grade.

[ian Howell]

Using 20/50 at present, have tried straight 40 and 30 in the past, but being an old (VERY) Javelin man I thought I would try 20/50.

Either way, it seems to make very little difference to the 'Warm 'pressure, so as you previously pointed out, as long as the bearings are getting oil . . . .