Rb30 Oil Pump Dilemma

[PSI086]

I've put together a new single cam RB30 and fitted an RB25DET oil pump as the VLT pump was worn on the drive flats. I fitted the spring from the VLT pump to the RB25 pump and used the existing RB25 piston. After finding the oil pressure a bit too low I've done a bit of measuring after pulling 3 pumps apart (RB30ET, RB25DET and RB26DETT) and also found a few differences between all the pumps. So I'm now scratching my head with what do do.

I know the RB30 pump has around 65psi when the engine is first started (cold) so I'd like to try and keep it as close to that as possible. I presume the RB25 pump will have sky high pressure if I reinstall the stock spring into that as its a much higher pressure spring. In saying that the relief hole in the cylinder where the piston is fitted is 5mm closer to the bottom than the RB30 pump, so the piston doesn't have to travel as far to let pressure out. As you can see from the pictures the piston is also totally different in design to the other pumps even though all 3 measure up identically in size. The threaded section on the actual pump also protrudes further than the other 2 pumps which would have been easily overcome if the relief holes were the same height in the bore. RB30 - 10mm from bottom of the bore, RB25 - 5mm and RB26 - 7mm.

I'm after feedback from anyone who has either fitted the RB25 pump as it is and had normal operating pressure for the single cam motor or has fitted different springs, pistons, shims, etc so that the pressure will be spot on.

At the moment I'm thinking of running the RB30 spring and piston with a 5mm shim in it which will bring the spring up so it protrudes the same distance from the bore therefore spring pressure will be correct once the retaining bolt is screwed in. But then theres the difference in relief hole height (5mm) so I'm not sure how well that will work as the piston will only move 5mm instead of 10mm to let pressure out. Will this affect my oil pressure much? The design of the piston from the RB25 pump also looks as though it will let pressure out without moving due to the holes and groove in it

Heres a few photos of what I've found

The RB26 retaining bolt also has a deeper hole inside of it

Edited September 4, 2009 by PSI086

[shanef]

Seeing as to fix ur problem one way or another you have to remove the sump, so just find a good condition rb30 pump and put that in, and hey presto!

[psi]

...OR,

be a little out there and weld a large bung fitting into the bottom of the sump (where the oil pump releif vavle is).

Just unscrew the bung and you can get at the vavle!

we did this on an old (R31) Race engine that gave us oiling hell...

I will be doing it to my 25/30 as well (bit over the top, but i HATE taking the sump off!)

does that help ya?

[PSI086]

I did actually consider doing that while the sump is off. At least that way I can swap and change bits and pieces

[psi]

DO it.. you wont look back!

[T04GTR]

use the relief valve for the pump your using.

on a 26 cold oil pressure is around 100psi depending on the oil clearances in the engine.