High Oil Pressure

[zKars]

My understanding of oil pressure is that is caused by the balance of two controlling factors. One is the internal relief valve in the oil pump, and the other is main and rod bearing clearance. The pump relief is a spring pressure controlled device that just allows internal bypass at a certain max pressure, but the bearing clearance and pump volume determine the overall pressure over the range of normal operating conditions.

I can't see one bad bearing causing high pressure. When the pump relief valve sticks, the pressure gauge becomes a tach, ie rpm determines pressure and it can quickly get WAY above 60 at as little as 3k. Doesn't sound like your case.

Time to take it apart and diagnose. If its one bearing seized and the other have correct clearance and no sign of scoring and starvation, likely just a blocked passage to that bearing and bad luck...

[Patcon]

I hate that. I have built a number of engines Z's and others. I agree the bearing clearances on a polished crank running standard bearings should be on the loose side not too tight. I am curious to see which bearings or whether it's all of them. Take some pictures of each bearing and keep them in order. I have had motors destroyed like this but from different circumstances. I have one motor I built that has excessive oil pressure that I have yet to identify. I tend to agree that you had a blockage or partial blockage somewhere, junk out of the filter, a piece of gasket or a loose piece of RTV something. If the bearings are evenly worn and cooked It would have to be a serious blockage to blank the whole crank. Remember that you may not be able to remove the bearings from the crank. I had one fail like that too, they were welded on. I really feel for the loss of time, parts and machine work.

Charles

[madkaw]

Did you plastigauge all bearings?

[Lazeum]

I'm sorry also to hear that. Was it on your L28 with L24 crank?

I'm posting also to follow up on your findings

Bleed valve from the oil pump should be able to maintain 60psi at 3000rpm but also at 6000rpm. Could too high pressure at 3000rpm be related to by-pass restriction since it should be capable to do the job also at twice the rpm?

I would suspect something is going on inside the pump. I would also check galleries inside the block between the sender and the pump.

Regarding crankshaft clearance, too much clearance would make the oil layer to fail withstanding high pressure resulting in metal contact => failure.

I don't know what are the limits, they might not be that small.

Bearing failure could also come from clogged galleries inside crankshaft.

[Patcon]

I also second Madkaw's question. I assume you assembled the bottom end did you plasti-gage or mic your clearances?

C

[Diseazd]

Lazeum.....No it was the L24 block and crank on the gold 71.....I didn't use plastigage, but every standard on standard I've ever plastigaged has been acceptable, plus the crank spun effortlessly with the mains torqued. Besides, the pressure increased later, if it had been a clearance issue, it should have started from the first start up, but you're correct, it could have been an out of tolerance shell, but I don't think so. I'm bummed and haven't pulled the engine yet, but will keep everyone informed. Luckily, I have the L28 motor with the L24 crank and rods almost finished....it didn't have anywhere to go......now it does.....could be the gods.

Edited July 28, 2013 by Diseazd

[Travel'n Man]

Sorry for the bad luck - but the good part is the new engine is going to rock. Let us know about the new configuration with the crank and rods.

[Lazeum]

You've got a golden back-up At least, there's some positive outcome to this failure.

[Diseazd]

This is the engine before installation .......sure was pretty.

[Diseazd]

Thanks everyone for your condolences in my time of need........you guys are the best!

[Captain Obvious]

Woof. That sucks... Hope you get to the bottom of it.

Hoping to help in that endeavor, I'm no hydraulics expert, but I think you can rule out filter bypass problems.

The purpose of the bypass on the filter is that as the filter gets dirty, the pressure required to force oil through it goes up. If the pressure differential between inlet and outlet of the filer gets too high (like in the event of a badly clogged filter), the bypass valve will be forced open and unfiltered oil will pass around the filter instead of through it. The engine will still get oil and the theory is that even unfiltered oil is better than no oil at all. There is a filter bypass valve built into the block, and most commercial filters have one built into the filter themselves.

All that said... The opening pressure differential across the filter required to open the filter bypass is only a couple psi. I didn't look it up, but probably about five psi or so. Remember that you're only concerned with the differential between inlet and outlet. The absolute pressures don't matter. The point is that a clogged filter should not result in significantly higher oil pressure. The pressure increase even from a completely blocked filter should only be the pressure required to force open the bypass.

Here's a snippet from the FSM that shows the lube scheme. You can see the pressure relief valve in the pump and the bypass valve on the filter:

As for the pressure relief valve getting plugged with something? I doubt it. It's built right into the pump and essentially short circuits the pump. If the pump pressure gets too high (and we're talking absolute here) it will force open a valve that connects the outlet of the pump back to the inlet. The passages are large and if you've got a goober in there big enough to clog them, then you've got other serious issues.

The valve might stick shut, but I'd be surprised if it got clogged shut.

My theory is that as your bearings started to weld and the clearances went away, you started bouncing off the pressure relief in the pump. Prior to that time, your pressure was limited by the bearings, but when the bearings went south, the pressure went up until the pressure relief took over.

Maybe you spun a bearing or five and blocked the oil supply holes to the crank as a result? Is that even possible?

My condolences...

[Jeff G 78]

OMG Guy, this is terrible! I'm so sorry to hear that your Safari Gold car is down.

The only thing I can think of is if there was a blockage in one of the oil galleys that occurred at the machine shop or shortly after startup. If a piece of flash got lodged in an oil passage, it could create the high pressure and starve the bearings. Hopefully, the damage is limited and has not ruined everything in the engine.

Have you drained the pan to see how much metal is in the oil?

Please let us know what happened.