SBC & oil pressure at idle

[Tom68]

Yes, this is a stock GM spring.

When I spun the pump, I got a good amount of oil on the rockers (all of them). so I was convinced all was good. Didn't check for pressure as I don't have an oil pressure gauge to do it with and I normally fire the engine up in the car and look at the car's oil pressure gauge to verify.

You'd know without a gauge that it's alright, 38 psi would have worked the drill hard and tried to wind the drill backwards when you stopped.

[RDY4WAR]

What temperature was that though? The high today in Belgium was about 55°F. At 55°F, the 15W-40 oil is 400-500 cSt. It's about 150 cSt @ 85°F and about 100 cSt @ 100°F. It's much easier on the drill to pump 100-150 cSt oil than it is 400-500 cSt oil. If the dyno guy's drill was struggling to stir that molasses, wasn't able to get much rpm, that would explain that lower pressure.

Still though, I don't see a problem. The drill could lose half its rpm due to higher viscosity oil, but the engine will still idle at the same rpm. (just with more power loss / fuel consumption to turn the pump)

[Belgian1979]

Got it back. It doesn't make any pressure at all which is strange as when I had it here I had resistance on the drill and could pump oil up to the rockers quite fast. So something is wrong here. Going to dig into it.

[rebelyell]

Got it back. It doesn't make any pressure at all which is strange as when I had it here I had resistance on the drill and could pump oil up to the rockers quite fast. So something is wrong here. Going to dig into it.

What If ?
What if the plug under #5 cap was R&R --- But was driven in too far --- partially obstructing an "oil filter" galley ? If so, could that affect pressure ?

[Belgian1979]

Took the pan off, oil pump, took off cap nr 5 and took out the spring in the oil pump.
Plug is definately under number 5 so that scenario we can leave behind.
Nothing particular that I can note about the oil pump (Melling M55). Can very easily push the plunjer for the bypass back. Took the spring apart but nothing specific that I can see. The plunjer of the bypass doesn't come out, but blowing air into the bypass passage returns it to the inlet side, so that's ok I think.

PS: engine was not yet run. So there is no real damage. It's however a PIA.

[prairiehotrodder]

i had a 377 SBC (400 block, 350 crank) that had low oil pressure and no matter what i did i couldn't fix it. However i was just a kid and didn't really know what i was doing or how to measure stuff correctly. It had about 5 psi at hot idle and it never went above about 50 psi even when revved to 7500 rpm. Finally i just gave up and drove the thing. It lasted for about 4 years of a 19 year old kid torture. Ran high 11's in a 65 chevy pickup with 4.88 gears. It never did blow up but eventually cracked a cylinder and started using coolant. My machinist told me that it can be caused by loose fitting cam bearings which he said was common on 400 blocks. Don't know if thats true.
Brian

[Belgian1979]

The shop (fwiw) said that the pressure was really slow to build up. Didn't get that feeling when I was priming the system, had a lot of resistance when turning it with the drill. So this has me stumped.

[Tom68]

Can't believe you've dropped the sump for half a look. You either run the motor, or drop the sump pull the pump and test it or you strip and remeasure. I'd run it.

[Belgian1979]

Can't believe you've dropped the sump for half a look. You either run the motor, or drop the sump pull the pump and test it or you strip and remeasure. I'd run it.

I'm going to change the spring anyhow, so I had to drop the pan. Will retry and also try another filter. Just to be sure.

[Tom68]

Can't believe you've dropped the sump for half a look. You either run the motor, or drop the sump pull the pump and test it or you strip and remeasure. I'd run it.

I'm going to change the spring anyhow, so I had to drop the pan. Will retry and also try another filter. Just to be sure.

I just saw the post where you say you now have 'no pressure ?? have you blown a plug out the front of an oil gallery or something.

[Belgian1979]

Can't believe you've dropped the sump for half a look. You either run the motor, or drop the sump pull the pump and test it or you strip and remeasure. I'd run it.

I'm going to change the spring anyhow, so I had to drop the pan. Will retry and also try another filter. Just to be sure.

I just saw the post where you say you now have 'no pressure ?? have you blown a plug out the front of an oil gallery or something.

Don't know , haven't taken the timing cover/waterpump off. Didn't find a plug in the pan if that's what you mean.
Going to replace the spring, temporary mount the pan back with the old gasket and start pumping oil. Attach the line of the pressure tester to various locations and see where I have pressure and where not.

[Tom68]

I'm going to change the spring anyhow, so I had to drop the pan. Will retry and also try another filter. Just to be sure.

I just saw the post where you say you now have 'no pressure ?? have you blown a plug out the front of an oil gallery or something.

Don't know , haven't taken the timing cover/waterpump off. Didn't find a plug in the pan if that's what you mean.
Going to replace the spring, temporary mount the pan back with the old gasket and start pumping oil. Attach the line of the pressure tester to various locations and see where I have pressure and where not.

No pressure is no pressure. You could pull the timing cover whilst the sumps off, put the sump back on, spin the pump and see if there's a flood of oil behind the timing gear.

[fabr]

After going that far just pull the cam gear off and look.

[fabr]

If I was betting I would put a few bucks on the pump bypass piston was stuck open. Check it for free operation when all bolted up on engine. Pull the spring out and verify free motion. Verify it does not stick even a little in the full open position.

Did you install the gallery plugs yourself? If so were they the drive in cups and did they go in snug and then were staked in place? That would be the second most likely culprit.

It's either of those or you have some seriously screwed up clearances . Cam bearings,rods or mains. That's about the only things it can be.

If you had started the engine even once maybe the distributor gear could have a sheared drive pin. But since you say the dyno guys also tried to prime it and got some pressure that is ruled out as any possibility. It will be interesting in what you discover.

[Belgian1979]

If I was betting I would put a few bucks on the pump bypass piston was stuck open. Check it for free operation when all bolted up on engine. Pull the spring out and verify free motion. Verify it does not stick even a little in the full open position.

Did you install the gallery plugs yourself? If so were they the drive in cups and did they go in snug and then were staked in place? That would be the second most likely culprit.

It's either of those or you have some seriously screwed up clearances . Cam bearings,rods or mains. That's about the only things it can be.

If you had started the engine even once maybe the distributor gear could have a sheared drive pin. But since you say the dyno guys also tried to prime it and got some pressure that is ruled out as any possibility. It will be interesting in what you discover.

All well noted. Not going to be here for a couple of days. Will be in the weekend.
I had the impression the piston of the bypass was not freely moving. I would think it would need to slide by itself which it wasn’t doing and it didn’t want to come out either (new Melling BTW).
A question: if I remember correctly these were pipe plugs.
In my other block (86 up -1piece rear seal) these front pipe plugs were some strange size that couldn’t be tapped and sit really deep. How do you stake these plugs?