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Discussion Starter · #1 ·
I just started the 496 yesterday and found @ idle 70 psi, but if you raise it to 2500 rpm pressure starts falling down steadily, and once you let it idle goes back up. When you pop the accelerator quickly it also mtries to fall. Any ideas what would cause this?
 

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I just started the 496 yesterday and found @ idle 70 psi, but if you raise it to 2500 rpm pressure starts falling down steadily, and once you let it idle goes back up. When you pop the accelerator quickly it also mtries to fall. Any ideas what would cause this?
doesnt sound good,
sounds like pump/pick up tube? what u running for pan as in size ? Im sure your running the correct one for stroker !
What u running for oil pump? hopefully tube is pressed on and brazed? I do this to all my big block builds.
keep us posted
 

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Discussion Starter · #3 ·
7 quart milidon. Measured to have 3/8" clearance to bottom . It's a new mellings hi volume. Have the lifters ( solid roller 741 lift ) set loose @ 28, could that cause it to loose pressure?
 

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You probably should try another guage, but I agree with the other Randy it doesn't sound good. If it's not the guage I would be hoping it's the oil pump.
 

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Some things that can cause this

Oil pickup fell off , sometimes screen windage trays cause this problem on stoker motors.
Oil not returning from the top of the motor, check that the oil drain back holes in the heads are not partially blocked. by gasket or mismatched holes , oil pump pick up correct distance from bottom of pan.

Regards, Robert
 

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Discussion Starter · #6 ·
It has only been run about 15-20 seconds at a time, I don't think it would have enough time to pump the oil to the top completely. Shouldn't 3/8" clearance to pan be sufficient? The oil is Castrol 20-50.
 

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All of the above is correct, except that the lash won't affect it at all, unless a lifter popped completely out of its bore.

The other thing that can cause this is a massive internal leak. I had one once like this with a custom manifold that had the distributor up too high and its oil groove not aligned properly with the one in the block.

There are other things that can leak too. Oil pump not tight, or trash between it and the main cap. Oiling holes in the lifters exposed. Narrow rod bearings for a big fillet crankshaft exposing rod journal oil holes. I think there are others.
 

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Discussion Starter · #8 ·
I didn't think the lash would matter, but was told by someone else it might. Interesting about the dist., I did change distributor, but the heads and manifold are the same that came out of the 439. I'll pull the pan and check the pickup first. Luckily it's in the nova and not the 55. lol thanks everyone Jim. Shouldn't the slot be the same on all dist?
 

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your symptom indicates the pump is starving for oil
If it was a internal oil leak your pressure would be low at idle as well as higher rpms, think about the pump at low rpms its not pumping near as much as at higher rpms, so if it was a internal leak it would effect idle the most ( unless its a lifter being bounced up high enough that the oil galley gets exposed that only occurs at higher rpms ). Try temporarily overfilling the oil pan with a extra quart or 2 and see if the symptoms change

Regards, Robert
 

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Discussion Starter · #10 ·
Tried adding extra quart yesterday with no avail. Will let ya'll know after the pan comes off. I think the pickup came loose or is too close to bottom of pan. Hopefully today or tomorrow. Gonna be a bad to the bone motor though. 14 to 1 comp. Engine builder said it should make over 100 hp per cylinder plus 225 shot of nitrous in a 2300 pound tube chassis 67 nova. Hold On!!!!!!!!!!!!!!
 

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"If it was a internal oil leak your pressure would be low at idle as well as higher rpms, think about the pump at low rpms its not pumping near as much as at higher rpms, so if it was a internal leak it would effect idle the most"

The engine that I mentioned had the symptoms mentioned, plus this. When you'd fire it cold, it would have normal oil pressure. As it warmed up, at some point it would lose all oil pressure. The pressure loss wouldn't occur at idle, it would occur when you opened the throttle. After it lost pressure, it wouldn't come back until you let it cool. I think that the erroneous gap in the distributor body to block fit was small enough that it didn't leak nearly as much when the oil was cold, and the pump could keep up.

The other key thing on my experience was that this was an engine that never was driven, all this occurred in the shop.

I tore that engine down and reassembled it twice looking for new problems. I had run the manifold before, so I didn't suspect it or the distributor at first. I even dropped the pan and ran the pump with a drill while turning the engine over by hand with the pump pushing oil into the engine with no pan on it. That was messy!

Anyway, I finally found the distributor problem. I also found that there were oiling holes in the lifters that were being exposed at max. lift. And I found the narrow bearing problem. I also found that my machinist had left out the plug above the oil pump which separates the supply and return passages for the oil filter. (That didn't have anything to do with pressure, but it was a total bypassing of the filter.) I fixed all that and the engine ran fine. With all the disassembly and assembly, no oil pan experiment, etc., about 2 months passed by. Quite a frustrating ordeal.

Last thing, I think the oil groove in the distributor body is the same for everything but a 265 small block. Remember that SBC and BBC distributors are generally interchangeable.

I feel sure the distributor problem was the main culprit. The other things were just there and along for the ride, and weren't helping anything.
 

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Hi, in response to your problem, a friend of mine built a 434 small block for drag racing when he started it he had a problem similiar to yours. he called me and asked my opinion, i went to his garage to help him. what had happened his son put the oil pan on and didnt check pick up to oil pan clearance. he tightened oil pan against pick up shutting off oil supply. check pick up to oil pan clearance. hope this helps
 

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Discussion Starter · #14 ·
Update the problem was that the pickup tube was against the bottom of the pan. Reshaped it to 3/8" clearance and worked great. Thanks for the imput everyone. Runs great now hoping for low 9's on the motor. We'll see
 

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Update the problem was that the pickup tube was against the bottom of the pan. Reshaped it to 3/8" clearance and worked great. Thanks for the imput everyone. Runs great now hoping for low 9's on the motor. We'll see
glad things worked out for u, thats great, Hate to say it, but things could of been worse, but wasnt :wavey:
:wavey:
 

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For what its worth, I have also seen a collapsed oil filter cause this same problem. Idles with plenty of pressure but as the rpm's climb the oil pressure drops. Changed filter and all was fine.
Glad you got it fixed. That little nova looks like it will be quick :)
 

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If it's a Chevy and this happened to you, either your oil filter bypass valve has been plugged or it's not functioning.
 
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