THE MINI MAG. Volume 2 No.9
  September 2000

Vol.2 Home Page | Index Page


Adjustable oil pressure release valve.
Construction / Installation.

The problem with the design of the pressure relief valve is that the valve plunger is a cylinder which is tightly confined along its length. One small shaving is all that's needed to cause it to jam open or closed. All that's really required is enough of a valve to seal against the seat. A ball bearing can replace the plunger and get around all the problems.

Here's how it's done:

1. Remove the oil pressure relief valve dome nut (1" wrench).

2. Remove the pressure spring.

3. Insert a finger into the hole and extract the plunger.

4. Drill and tap a 5/16" UNF thread in the centre of the dome nut, thread a nut onto a 2" bolt and screw it into the dome nut.

5. Cut 3 coils off the pressure spring and roll the last coil over to make a nice square bearing area. To be able to use the bolt as an adjuster, you'll need to ensure the spring bears upon it properly. This can be accomplished by either searching around until you find an appropriate washer, or make up a thin steel disk which just fits inside the diameter of the dome nut.

6. Obtain a 1/2" diameter ball bearing. CV joints are a good source for these, or go to a bearing supply shop who will likely just give you one since it's not worth their while to write it up.

7. Insert the ball bearing, then the spring and capture it all with the dome nut.

8. Screw the adjuster all the way out and start the engine. Watch the pressure gauge closely: if it reads: >60 PSI, shut the engine down and take another coil off the spring. <55 PSI, close enough, <50 but >20 psi, go to the engine and screw in the bolt until the gauge reads 50 PSI; <20 PSI, you've buggered a spring and you need to find another one! Mine ended up needing 4 coils cut off, but I started with 3.

9. Once you've set the pressure you want, I recommend 50 PSI, set the lock nut.

An interesting thing about this setup is that the oil pressure stays at 50 PSI. Cold starts with thick oil: 50 PSI. Hot starts with thin oil: 50 PSI. Highway running at 90 MPH: 50 PSI. Hot idling: 50 PSI. If the oil pressure flutters or varies widely, shorten the spring and pack the space between the spring and dome nut with washers to reduce the operating range of the release valve.

Ed: Taken from U.K web site. This is passed on for your information. No responsibility taken by the editor or the Mini Owners Club.