Morris Minor Owners Club

Hi Folks,
After renewing the oil pressure relief valve system using ball bearing and spring instead of the bullet type that came out I notice on startup that the oil pressure reading is off the scale on the gauge but does drop back on warm up.
Is this acceptable or should I go back to the original bullet and spring system?

The relief valve is there to limit the max pressure when the oil is cold.
If you're going off scale, then it needs to be fixed.

What's the top of scale on your gauge?
Have you checked your gauge for accuracy against a known good gauge?

Max reading on the gauge is 80psi,
pressure relief should operate at 60psi although I have read on this forum of engines running at 80psi fully warmed up!
Just need to know if excessive oil pressure would cause damage.

One night the pressure relief valve jammed shut on mine. The engine felt laboured and the gauge, up to 100 psi, was as high as it could go. I stopped the motor and on restarting it was ok again. Drove home, keeping a close eye on the gauge.
The next day the results were a small bit of grit in the valve and a leaking gasket between the oil filter housing and block.

If the gauge has been pushed beyond the top reading - it will no longer be accurate. Why did you fit the ball?? This is a competition modification (I did it on my race/rally engines) - but yes the spring needs to be shortened - simply because the ball is 'thicker' than the bullet when installed. 70 psi is plenty pressure when hot - the ball should be able to dump enough oil to have no more than 90/100 psi when cold - but of course - you must never 'rev' a cold engine.

Thanks Roy, Got the ball from ESM thinking that it would seat better than the bullet, as you rightly say the ball puts more pressure on the spring which was why I had a bit of a job refitting the valve system.
I have now ordered a new bullet to replace the original one and will be refitting the valve when time and weather permit.

Or just shorten the spring!

When using the ball bearing instead of the standard plunger (Pt No: 12H865) you should use shorter and stronger spring (Pt No: AEA536) which has a free length of 66mm. Original oil pressure relief valve spring (Pt No: 6K853) has a free length of 73mm and is much weaker.
If finer control of the max oil pressure is required then use an adjustable pressure cap instead of the standard cap (Pt No: 12A1851). Adjustable pressure caps are available from the majority of 'A' Series Tuning Firms

The AEA 536 spring was specified for the S - but it will still be too strong for a ball..... Just cut a coil or two off the standard spring. it works !

If you are determined to cut the spring make sure that it is the remaining correctly formed end that sits on the ball bearing and the cut end sits inside the cap.

Indeed yes - I should have added that! Thanks Phil. I have tried the S spring in the past - and it still put the gauge off the clock when cold - which of course ruins the gauge.....

Just use the standard bullet, it works fine.
Remember if it ain't broke ..........

I agree for a road car. But I used the ball in my comp engines because there is virtually NO chance of it ever sticking....

Idealy when fitting a new oil pressure relief valve it should be lightly lapped in. Great care should be taken to ensure that the lapping paste DOES NOT get into the oil ways. BMC reccommended using Oil Pump Relief Valve Grinding Tool Pt No: 18G69 specificaly for the lapping of the relief valve but a piece of suitable hose pipe inserted into the valve will surfice. Make sure that all traces of lapping paste are removed from the valve seat, the valve and housing before fitting the valve and not forgetting to put a new washer under the cap.

The dowel handle of the valve grinding tool - with a twist of tape added - fits tightly in the valve.... Ball saves all that hassle!

bmcecosse wrote:The dowel handle of the valve grinding too - with a twist of tape added - fits tightly in the valve.... Ball saves all that hassle!

I agree, I believe I will just clip the spring!