MBC Racing

iTrader: (3)

Since these are G-rotor style pumps, what fails on them? If they start making low pressure what is the culprit? is it the valve taking a **** or increased clearance in the gears? What changed on 98 to the new ls1 pumps???

I really don't want to pull mine, but most likely will have to. Would be nice if I can just shim the spring or pull the spring and valve from the 45k mile lq9 motor I have sitting there.

eallanboggs

iTrader: (1)

How would changing the spring or shimming it increase pressure?

kyles2000z

iTrader: (8)

more clearance in gears i would think.

Notmyvette

iTrader: (1)

Unless I'm talking about volume, but changing the spring tighter in anyway possible is going to prevent the relief valve from bleeding off pressure as soon thus building more pressure....I think

01ssreda4

iTrader: (96)

If they bleed off pressure too soon then they would need to be replaced. I have had one do that before. Fatigued spring i suppose.

DaveX

Very good question. I don't see how the gears could wear out.

eallanboggs

iTrader: (1)

The job of the pressure relief is to relieve pressure over a threshold set by the strenght of the spring and shim if used. You add a shim or stronger spring and the point at which relief takes place is raised. Conversely, a weaker spring bleeds off pressure sooner. The pressure relief doesn't contol pressure or volume UNLESS you excede the threshold

TEE_99WS6

iTrader: (9)

Oil pumps DO NOT create pressure, they create oil flow, pressure is created by restriction, i.e. the clearance in the bearings. If you're oil pressure is bouncing around or getting real low, you need to check/change the bearings and check you're main,rod, and cam shaft journals for wear and taper. The only thing putting a shim will do to your oil pump is increase the point of pressure at which it would dump some oil back into the pan. Which wouldn't do you any good since you dont have that much pressure any way. Hope this helps.

98RedBird

iTrader: (77)

You're statement is only partially true. No, pumps do not create pressure, that is a true statement. They create flow and the restrictions throughout the system is what creates your pressure, as you said. Also, your statements regarding excess main/rod/cam bearing journal clearances contributing to lower oil pressures is also true.

However, I would never tell someone to jump straight in and suspect worn bearing clearances right off the bat unless the motor had 150K+ miles on it. Checking bearing clearances means tearing the motor down completely, which is completely pointless if it is in fact a weak pressure relief spring in the pump, or a faulty oil pressure sending unit. A fatigued spring CAN cause a pump to output low flow numbers, thus creating low pressure as seen by the driver.

For instance, if your pressure relief spring is so tired that it's opening at 5 psi, at 10psi you may have it open all the way and will be dumping a very good margin of your flow back to the pan right from the get go. Again, creating low pressure numbers.

Regardless, bearing clearances should be THE LAST thing that you check.

blackLS1m6

iTrader: (14)

Have you checked to see what the oil pressure is with a oil pressure tester gauge? I would start there. Do you hear any kind of valvetrain noise or engine noise?