VX 16V Oil Pressure relief valve

[ECR]

I have been chasing the reason for low oil pressure on my spare engine. It had done less than 1000 miles after a rebuild but ran worryingly low pressure on trackdays. I stripped the relief valve from the pump, polished the piston, and added spacers under the spring. This improved matters but only very slightly. I decided to look at the main and big end bearings to see if i had somehow damaged them. All looked fine there so I stripped and checked the oil pump. All was in tolerance but I linished the cover plate flat just to be sure. I started the engine an had exactly the same problem.

I stripped out the pressure relief valve again and decided to compare it with the prv from an engine with known good pressure. The photo below shows the 2 side by side and the reason for the low oil pressure was obvious.You will see that the "good" prv has more coils of a larger gauge than the "bad"

 I have a collection of parts from old engines bought over the years as spares. The "bad" prv must have come from a vauxhall engine perhaps designed to run at lower pressure. The problem was that unless you have the 2 side by side, you don't notice the difference (especially when they are coated with oil).

Fitting the "good" prv cured the problem instantly. Note to self: If fitting parts from a different engine don't assume they are the same (even if they look the same) ......

Note:

The double hexagon on the "Low" prv is a mod I made to help when refitting to the pump and has no influence on pressures