20V CQ Tidy Up

[mcandmar]

I noticed in this AAN oil pump when I stripped it down there was a shim washer that I'd not seen before in the 7A or 3B pumps I'd stripped. It's not in ETKA either so wondered if anyone else had come across it? Net effect will be to raise the peak oil pressure. Looks OEM as it is black zinc plated and thicker than an off-the-shelf washer.

I believe its 034 115 197 in the parts system, 100% meant to be there, and as you found it only seems to be fitted to ABY/AAN/ADU engines.

[Thuppu]

Hmm, don't know how it can rise the oil pressure? Can someone explain?

[Error404]

The washer puts more pre-tension on the relief valve spring, so it takes more oil pressure to force the relief valve open. Effect is the peak pressure is raised.

[Greg_S]

that makes sense, not something I would have considered though. Good move on oil pump with vaseline too

[AndyP]

The washer puts more pre-tension on the relief valve spring, so it takes more oil pressure to force the relief valve open. Effect is the peak pressure is raised.

But under normal operating conditions you'll only see peak pressure when something is wrong or maybe from cold, right?

[Error404]

I was thinking about this earlier and I guessed the pump must begin to produce excess flow/pressure somewhere before the peak torque of the standard map? I guess that would be the point of the rpm range where most force was exerted on the bearings?

[mcandmar]

I dont know what pressure it peaks at as i've never plumbed a proper gauge in. But i suspect it opens instantly on a cold engine, or anything over 2000rpms on a warm engine. Or to put it another way if the dash pressure gauge pegs at 5bar, i would lay money its bleeding off excess pressure.

[Pirvu Eugen]

Too much oil pressure will push the tappets out and you will loose compression. Iff more than 5...5,5 bar cold...not ok.

[Thuppu]

Alex, can you measure and share the dimensions of the washer?

[Error404]

No problem

[andy10v]

It used to be fairly common practice to shim to get more oil pressure, a few engine building books still mention it.

Does vaseline just dissolve in oil then?

[PRY4SNO]

Does vaseline just dissolve in oil then?

It's petroleum based, so it'll break down under heat and shouldn't negatively affect anything. I think.

[Error404]

Andy, same as I have seen - all of the blueprinting books I have read suggest shimming the relief valve spring to increase oil pressure and also to pack the pump drives with petroleum jelly for instant oil pickup. I'll measure this shim washer in a bit.
It will be an upgrade for 3B owners for sure, as its not there to begin with

[andy10v]

Yup its petroleum jelly in both books I am reading just now.

Is the pressure relief valve otherwise identical on 7A/3B, they just shimmed in on AAN?

Something else to do then? Or as the car was fine previously don't ****** it about?

[Error404]

I've got a 3B pump here. When I get time to measure the washer for Thomas, I'll compare the two relief valve assemblies.