R19KET

James,

The up rated oil pumps (more a case of modified) aren't shimmed, nor do they increase the oil pressure.

The up rated/modified oil pumps have the original piston/plunger replaced with one that doesn't have the groove in.

The original plungers are notorious for "sticking", or "jamming", more often than not, in the open position, causing a drop, or loss of oil pressure.

It may only get stuck for a fraction of a second, and may not even be detected on an oil pressure gauge, but it can be enough for a bearing to pick up.

Personally, I wouldn't recommend shimming the spring, I don't believe the standard oil pressure is an issue. 6bar is already high compared to many other performance engines.

Mark.

jameswrx

iTrader: (4)

Thanks for the replies..

So when high performance Impreza engines are built, and an 'uprated' oil pump is used, is the main issue, to solve the stiction?.

Are people believing that more oil pressure is needed?

Mark, when you say about a bearing picking up, do you think that even a momentary drop in oil pressure removes the sandwich of oil between bearing and crank?, I would assume a longer period of pressure drop to have this effect, but perhaps not one that doesn't register on the gauge?. Or did I missunderstand you?.

remember reading something from a rolls royce mechanic about pressure and bearings, running on 5-6psi through bearings. I found reading about older cars more consistent as far as things like this go.

hypoluxa

James,

Shimming the relief valve will not increase pressure at low revs. It will allow for an increase at high revs.

Stock cracking pressure for the relief valve from memory is 5.5 bar. The low pressure warning switch is set for 0.2 bar. Oil squirters open a tad under 4 bar. So shimming is unnecessary. As Mark and Bob mentioned it's the piston that needs attention.

Tight bearing clearances will increase pressure because the flow of oil is restricted, as loose clearances lead to lower pressures but better flow (and lubrication). I run different clearances to OEM, and consequently have different pressures (but I also have a baffled sump and modified pick up).

BTW a rod bearing about to meet it's maker will show up as a decrease in the increase of pressure as revs rise. Or just a decrease if your unlucky. Whether you spot this is another matter though.

jameswrx

iTrader: (4)

Thanks for clarfying guys.

EMS

Do you need a complete pump assembly, or is it possible only to change the plunger for a better one?

Mark.

EMS

?

Pavlo

if you can get a plunger, that can be enough. The RCM pump is also supposed to have the internals cleaned up, deburred etc.

Paul

hypoluxa

You can buy them separately.

jameswrx

iTrader: (4)

Thought i'd start another thread so as not to go off on hypoluxa's thread here

One question for people with uprated oil pumps; are you running looser tolerences in the engine?, whats the main idea behind it?.

I thought about an uprated oil pump a while ago, done some research and stumbled accross many things, like too much shimming, not good(thats why I said about the bolt, from what I read, apart from damage of piston, more heat is generated), also read that the main reason racing engines use them is because they have larger bearing tolerences to remove heat from the bearing/friction area. Thats why I asked the question about tolerences.

The thing I remember(and correct me if my memory serves me wrong), is that uprating the relief valve is only going to benefit(increase oil pressure) the low engine speed running, and that too much pressure with cold oil is a bad thing.

I didn't see any use in uprating the oil pump in my std engined wrx, was I wrong?.

[Edited by jameswrx - 6/7/2003 10:32:32 PM]

Bob Rawle

A well modified oil pump will not provide extra pressure, the pressure relief valve in the std pump is prone to stiction, a properly modified oil pump involves the elimination of this possibility. Some modified pumps are shimmed to increase pressure but do not address the stiction issue, unless that is done the pump is no better than "standard".

edited for typo !!

[Edited by Bob Rawle - 6/7/2003 11:17:06 PM]

R19KET

James,

There is only ONE reason to use the modified pump, over a stock one, and yes, that is hopefully prevent stiction, or jamming. It's the only thing the modification is designed to do.

Even in a fraction of a second the engine turned several times. A bearing can "pick up" without actually failing there, and then. It will also depend on the engine load when it happens, and how often stiction occurs.

One problem, is that it can be very difficult to identify if the plunger has an issue, without stripping it for inspection, and this is a pain, unless done at the same time as a cam belt change.

Mark.






[Edited by R19KET - 6/8/2003 12:27:16 AM]