Thread: Baffeling Oil Pressure problem

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I have a problem with a SBC 400.
The eninge Spec:
Eagle steel crank, 6" rods, Melling HV pump with strongest oil relief spring, roller cam, roller rockers, no oil restrictors (Crane adviced against), Milodon 31145 sump. Valvoline racing oil.

Oil pressure was low at idle, so I striped the motor, and found all bottom end bearings damaged from oil starvation.
So I replaced the bearings, polished the crank, and got 2-2.5 thou clearance through out. I checked the pump over, and ensured that the relief piston was sliding freely.

Started the motor, and got 35lbs hot at low RPM idle. Rev the motor, and the pressure climbs to about 70lbs at about 6500, raising the RPM causes the pressure to drop to about 45lbs at 6500.

I'm baffled.....
Limey

Sounds like the relief spring is coming open. 45 PSI should be plenty @6500 RPM..

The oiling system on a stock chevy is oustanding. Too much oil pressure is as bad as not enough. It will wash the bearings out, the oil needs to stay on the bearing long enough to lube and carry heat away. too much pressure passes the oil across the bearing to fast to do either. A high volume pump will suck the pan dry, not good. On a properly clearanced engine, stock oiling system is excellent, only a very few engines require a drysump or alteration of the oil system. This is just my opi.

Pressure drop at high RPM is a bad sign. The oil isn't getting to the pump for some reason. The sucker may be too close to the pan. I've heard about small blocks sucking the pan dry, but never actually seen it, and I've run them to 7500 RPM. with both stock and hi-volume pumps.

Did you check to see that the plug was installed in the galley under the rear main cap??

The pick up is just less than 1/2" off the bottom of the pan.
Techinspector, what plug are you refering to?
There is nothing below the rear main bearing other than the pump.
Do think that the high volume pump is too much? If so then why do Melling and others sell them?
Limey

"Techinspector, what plug are you refering to?
There is nothing below the rear main bearing other than the pump"

Sorry, below as in having the block on an engine stand and looking at the main caps.

If the pressure relief valve is opening at say 60lbs, then oil will flow through it while the pressure is over 60lbs. How can the pressure drop to below 60? Surely the valve should shut.
Has anyone had a problem with distributer leaking where it plugs the gallery?
Limey

I really stumped now!
I have tried some oil gallery restrictors. They don't seem to make any difference to my problem.
I ran the engine up, got in warm, and got about 75lbs at 6500RPM, then after a few seconds of holding, the pressure drops gradually to 60lbs, then a few seconds later dives to 40lbs, at which point of course I shut off. When I tried this previously, it carries on dropping even further! This is off load sat in the garage!

I have checked under the rocker covers immediately, and they are wet, but not flooded with oil, so the oil isn't been stored up there.

I drained the oil within 2 mins of shutting off, to see if it was full of air, but it isn't.

I'd convinced myself that the oil was getting back down into the pan, and thus the pan was being emptied by the pump. Now I'm not so sure.

Considering the pump..... If the oil relief valve will be blowing open, so it will be circulating oil back into the pump inlet. If that could cavitate the pump, then surely the ensuing droppng pressure would shut the valve again, and not drop to 40lbs.

I wonder if there is a windage problem, where the bottom of the motor is pressurizing so much that it's blowing the oil that should be falling into the sump back up the return holes in the block.

Has anyone got any ideas?

Limey

Have you tried a different gauge? Some engines set up a harmonic fluctuation in the oiling system that drives some gauges crazy. Electric gauges are notoriously finiky. Line-type ones need to be bled of all air to work right.

this is the plug that Mr. Tech was talking about:

http://www.sdpc2000.com/faq/kbhowto.asp?mt_sc=1

if it asks you to search, enter "oil" and check "SDPC" knowledge solutions. When the search returns, there are a list of topics on the right side....choose "small block chevy oil crisis" for an explanation
mike in tucson

could the crank be churning air into the oil?

The pump in the SBC is an high volume BBC pump. It has a relief valve that when the oil warms up it opens at 45. What you describe tells me it is an healthy system. My van has the same pump in my 383/350. It starts and goes way up. At idle it is 45, at high rpm it is 45.
When I fear oil starvation, I watch for pressure drops. Not jumps. A small block does not need high pressure, nor really high volume. I just like the high volume pump.
It sounds like you are like me. I get the willies on some things. In reality, if you have that pressure at idle, and at high speed, I would not lose an ounce of sleep. If you find trails in the oil, or it disappears, or drops to 0 at cruise, or drops while accelerating, I would definately freak out.
Steady pressure off idle is a good indication to me it is working as should be. I have the same pressure as you do in mine, and I feel real good about it.

I've tried a different gauge with the same results.

The block is a stock 400 ci (Casting '511), and I pretty sure the oil gallery plug under the rear main is in place, since when bearings failed all the debris was caught up in the filter, and the rest of the motor was clean. If the plug wasn't fitted, then the debris would bypass the filter and be all over the motor.

Anyone got any ideas?

Limey

Originally posted by Limey
I've tried a different gauge with the same results.

The block is a stock 400 ci (Casting '511), and I pretty sure the oil gallery plug under the rear main is in place, since when bearings failed all the debris was caught up in the filter, and the rest of the motor was clean. If the plug wasn't fitted, then the debris would bypass the filter and be all over the motor.

Anyone got any ideas?

Limey

I disagree. Not all the debri was caught up in the filter. I would be concerned about cam bearings. If you wiped the bottomend from oil starvation, why do you think the cam bearings were not treated to the same thing? Also did you clean the oil galleries out? I mean run a brush and soap through them and get them clean? A very small partical of dirt can distroy a bearing very quickly. Just my opi.