oil pressure problem

[79transam]

I have a 434 sbc. with a motown block. i ran this car last year and when i let off at the end of the track my oil pressure would drop to 10lbs. so i put a new pump in this year with a copper gasket and it wouldnt hardly carry any pressure at all when it warmed up. so i put another new pump in and removed the gasket. same problem still. i was using a bolt on pump screen, so i removed this pump and brazed the screen. i dont think its sealed 100% but its prob pretty close. so today i take it out and it will carry 60lbs of pressure for a good while, if i get on it or cont. quick reving it it will drop down to almost 0 then climb back up to 20lbs and may hit 40 but if i rev on it it drops down as soon as i let off the throttle. im stumped. i run 20/w50 lucas oil with a wix racing filter. and yes ive tried a different gauge. any help will be greatly appreciated

[Rob Petrie E395]

A couple of things come to mind after reading your post.
1. Have you tried a different oil filter. I know it sounds crazy but there are people who let a car sit all winter without changing the oil and filter. If the filter was collapsed and you never changed it just pumps well you get the idea
2. Did you remove the bypass spring before you brazed the pickup on? If it gets too much heat while brazing the inlet on it will get weak and can cause low oil pressure
3. Define pretty close. If there is a leak couldnt it pull air instead of oil? I could be wrong but I would think it would be easier to pull air through a gap than 20W50 through the pick up.
4. How old is the engine? could it have been built with loose bearing clearances and now that its got some wear on it its way too loose. Sounds kind of like when the oil is cold its ok but when the oil gets hot and thins out a bit its loosing oil pressure couldnt that be a sign of too much clearnace somewhere.
I am no engine builder by any means but thought I would throw it on here. I am sure if I am a idiot someone will tell you in a minute. LOL

[79transam]

the engine has prob 75 passes on it. it is a new filter just put it on at the initial start up this year. no the bypass spring was still in it when we brazed it. it is the same problem as before the brazing though. i ordered a new pump from competition products with a bolt on pick up i guess i will try this to. im sure it would suck air easier than pulling the oil. when we brazed it we sprayed some soapy water and shot air into the pump to see how well it was sealed and it only had a couple of small leaks. but im for sure not ruling that out. im honestly stumped.

[Rob Petrie E395]

Have you pulled some caps and looked at the rods and mains to see how they look and check some clearances? Another thing that comes to mind is this scenario.

Something was not right from the get go (IE not enoughf oil in the pan, pan that could not controll the oil ect) So when you crossed the finish line the pan was already low on oil or the pan could not controll it. You hit the brakes to slow down and whats in the pan goes forward away from the pickup uncovering it and oil pressure went low and hurt one or more bearings.

[Phillip marvetz]

I have had exactly what Rob is desribing. It hurt 1 rod bearing and was very low on pressure once warm at a idle. Never made any noise just lost oil pressure and this on a car with exhaust so I would have heard it knocking. When I dropped the pan the bearings all looked fine but one had lost it's tension in the cap, I almost reused it it looked that good. I put new bearings in with the old pump and it was back to idling hot at 40psi in gear again just new and went all last season like that.

[Mike Taylor 3601]

Your original problem sounded like oil getting away from pickup,Your next problem sounds familiar,you did'nt say what pump you put in when you changed,but I ran into problems w/ 3/4 pickup hex drive pumps that melling has,they idle good and drop pressure when rev'd.I sold several and everyone has been took back out& replaced for that reason,replaced with 5/8 pickup HV melling select pump and fixed it.
It acted like cavatation,but could'nt get to stop tried different pickups,clearances on pickup,overfill w/oil, just switched to 5/8 pickup pump and fixed everytime.
Years ago we used run 3/4 pickup bbc pumps in sbc without any problems,so I don't know why we could'nt get those pumps to work,I remember comparing pumps and could see no difference other than pickup diameter.
Mike Taylor 3601

[Pvt Parts]

Originally Posted by Rob Petrie E395

Have you pulled some caps and looked at the rods and mains to see how they look and check some clearances? Another thing that comes to mind is this scenario.

Something was not right from the get go (IE not enoughf oil in the pan, pan that could not controll the oil ect) So when you crossed the finish line the pan was already low on oil or the pan could not controll it. You hit the brakes to slow down and whats in the pan goes forward away from the pickup uncovering it and oil pressure went low and hurt one or more bearings.

X2

Yeah, I'd be pulling some caps and checking bearings and crank. I had a Z28 that did that very same thing about 3 months after a rebuild with a new crank. I pulled the motor out and apparently the crank had not been tuftrided. It looked like it had 200,000 miles on it. GM warrantied the crank and I was back in business.

[79transam]

i checked the bearings over the winter, just visually when i put the first new pump in. they all still looked brand new. i didnt get this motor in my car until late in the season and it still looked great.

[CrateCamaro]

I agree with the others....could be a pickup to pan clearance issue or a windage issue. Another thing that wasnt mentioned is this...I have seen pipe pugs with tiny holes drilled in them for BBC to oil the chain....is it possible you didnt install an oil plug or you have put one of thses plugs with the tiny hole in it by accident?

If u have to try a new pump get a Mellings M55A pump...the best afordable alternative to a high dollar race pump. Thats what I have in my 377 Street engine with a Mowtown block and crossed drilled crank.....60+ psi of oil pressure and ive turned it well past 9000 RPM.

Also check the clearance between the front main cap and the timing cover...if its too tight oil will get trapped in the cover and not drain back to the pan. Mowtown blocks have a super thick main cap and some aluminum covers (even tin covers) come close to the cap. I know on a jesel front cover we actually had to machine a relief in the cap and the cover to allow the oil to pass by.

I also know that my oil pressure is as responsive as my tach.....when I rev it up the oil pressure moves just as quick but I always thought that was because of the priority oiling built into the block. Also not sure what pan you are running but there is a 1/4 pipe tap on the pan rail that is not level with the pan rail...im assuming if you didnt have this plugged you would have zero oil pressure but who knows. It doesnt go in all the way and the pipe plug actually needs to be ground down a bit to get the pan on...ive seen some big "bath tub" superstock pans that would cover this but im just brainstorming. Hopefully you can figure this out. One more thing...Usually if the filter is colapsed the oil pressure gets locked at a certain psi or is very sluggish and low...Ive had this happen with a Fram and a Quakerstate filter.....switched to a wix race filter and now I put them on everything.

[P Bailey]

You might want to check the cam bearings. Have seen the same problem after it warms up goes low on pressure. Phil