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Discussion Starter · #1 ·
Video Link below. What would cause my oil pressure to fluctuate like this? Constant cruising speed it will drop almost in a timed pattern. 400 Pontiac block stroked to 460, Solid roller cam. Wix Oil filter and I know the Filter bypass in housing is plugged. VR1 20w50 oil. I have already tried another mechanical gauge. Same result. Pressure taken from oil filter housing. 4an braided line. I have only had the car for 2 years and have put a good amount of street miles on it. Oil pressure rises with rpms quickly. Cold oil pressure at idle is 60psi +. When fully heat soaked I am getting 20psi in neutral and around 10 in gear. I am looking for input before I pull the motor out. Thanks.


 

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Discussion Starter · #5 ·
This just started? Try another gauge.
First thing I'd do is look at the rocker arms with it running. See if the flow changes with the gauge fluctuation. Thats an awful quick change on the gauge and the engine sound is steady.
That is a good idea. I tried another gauge with same results but I used the same line. Im wondering if its true about “bleeding” air out of the line?


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1) What is the scraping/squeeling noise I am hearing in the second video near the end when the pressure takes a dive? ....
2) Pump sucking a bit of air or bypass valve is funky, the sharp gauge movements make me think mechanical alignment something moving exposing a pressure passage causing a drop....How does the distributor body fit up in the block with oil galleies in these ponchos? anything like the chevies?

With solid rollers there is probly a lot of leakage from the lifter bands to oil galley positions, the lifter to pushrod seat cup, flow through the pushrod to rockers......
Would be an eye opener to run the engine with intake valley pan removed......
 

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Discussion Starter · #10 ·
1) What is the scraping/squeeling noise I am hearing in the second video near the end when the pressure takes a dive? ....
2) Pump sucking a bit of air or bypass valve is funky, the sharp gauge movements make me think mechanical alignment something moving exposing a pressure passage causing a drop....How does the distributor body fit up in the block with oil galleies in these ponchos? anything like the chevies?

With solid rollers there is probly a lot of leakage from the lifter bands to oil galley positions, the lifter to pushrod seat cup, flow through the pushrod to rockers......
Would be an eye opener to run the engine with intake valley pan removed......
I am not sure about that noise, I have only ever heard it in this video. Thats what I have heard before is the bypass can act up like that. I know there is a hidden plug behind the distributor in the block. But I was told if thats missing then I would have zero oil pressure. The valley pan think has been something I always thought would be cool. To make a clear valley pan and be able to see everything rolling.
 

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I use an old cast iron intake manifold cut in two, so just the distributor hole and last 2 bolts on each side remain. Makes priming and inspection of the oil flow around the lifters and cam bearings easy to see. There is more going on there than you would expect.
 

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I would start by getting a filter cutter, longacre makes a nice one and cut the filter open to spread the media out. Full of metallic debris it's rebuild time. No debris, I'd start by pulling the valve covers. idle with v/cs off, is oil coming up all pushrods? Can form a little splash guard. Pull distributor. Nothing obvious then it's going to be time to dive into the pump and bearings. Cam bearings can do weird things. If they are going out, filter would show the debris. Are you using a racing filter like a WIX racing? Seems like if someone blocked the bypass, and using 20w50... really need to use a free flowing racing filter. And that is some heavy oil to only have 10psi at idle in gear. I'm suspecting the lower end may need a good look see.
 

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I think the flutter could be from the 4an line and connection right at the filter. These fluctuations are majorly dampened by using a port further from the filter and/or smaller line. I don't think they're a problem.
I agree. The larger the line the more sensitive. I would try longer 1/8 inch line and see what happens. I had a 5/16 line on a Chevy and it looked just like that one, fluctuating all the time and very sensitive to the slightest engine rpm change.
 

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Discussion Starter · #16 ·
I would start by getting a filter cutter, longacre makes a nice one and cut the filter open to spread the media out. Full of metallic debris it's rebuild time. No debris, I'd start by pulling the valve covers. idle with v/cs off, is oil coming up all pushrods? Can form a little splash guard. Pull distributor. Nothing obvious then it's going to be time to dive into the pump and bearings. Cam bearings can do weird things. If they are going out, filter would show the debris. Are you using a racing filter like a WIX racing? Seems like if someone blocked the bypass, and using 20w50... really need to use a free flowing racing filter. And that is some heavy oil to only have 10psi at idle in gear. I'm suspecting the lower end may need a good look see.
Finally got around to it. I cut open the filter and there is some copper flakes. Not a ton of metal but it is noticable. Going to tear down and inspect.
 

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if you have debris , then maybe that points to it holding the bypass open. Since your initial post 3 months ago, I had the same problem.... some black 'something' sticking the bypass plunger in my BBC. Good luck, hope you found it early!
 

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Discussion Starter · #18 ·
Well I tore into and this motor was barely hanging in there. All bearings are toast and No. 2 main was spun. The main looks like it might have spun pulling it into the garage the last time I drove it. I know the guy I bought it from neglected it. Thoughts on cause?
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Hard to know if it was chicken or the egg, but Pontiac pumps, while reliable, are pretty susceptible to having trash get trapped between the check ball and seat. Maybe bearing clearances were garbage from the get go? Either way, glad to see you got it apart while things are still salvageable. Butler sells pressure tested and blueprinted high pressure pumps that I would recommend for the rebuild.
 
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