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To sum everything up I was having an oil pressure problem under load. After searching we found that the thrust bearing was out of spec at .010 as the book is .002-.008. I pulled the crankshaft out the bottom and had a machine shop check everything.
So I changed all the lower bearings. New mains, rods and GM pump. Everything is in spec. Mainly on the tight side of the bearing clearness. So I primed engine and oil flow was there but not great. My drill was kinda slow. I did spin the engine over while priming to get every rocker oil.
Fast Forward to the test drive. Oil pressure is good anywhere below 3k or if your cursing everything seems fine. Did a pull and guess what pressure drops off again. Can see in the video below that the gauge drops. I trust the electronic gauge as the mechanical one read the same results.
Talked to some people. One guy had this same problem and found it to be his lifters. He had a 383 lt1 as well. At this point I really don't care but I grab my super low mile ls7 lifters soak them in oil and swap them in. Get it all back together and oil flow at the lifters is low. Take if for a dive and no real change. Some oil flow but not what is needed. Seems it was a problem as well on the other lifters. Pull a valve cover and same as before the drive. Some oil but not enough. Should be a flow but its more like a squrit. At this point I am ready to scrap this whole car and move on.
Video Below is the pressure drop I am talking about. See how when I lift off throttle pressure jumps back up. Video is from today with the ls7 lifters.
- Spun a cam bearing and oil is not allowing to go threw
- Bad lifters tho doubt two sets had the same results.
- Block in the oil passage somewhere where I can not see it.
- Front oil passage plugs are leaking, misaligned, or missing. When I had the engine apart I did not notice anything wrong or out of place. Rear ones are good as no oil us pouring out the back of the engine.
- Cracked oil passage that is opening up under load.
- No windage tray issue?
As the problem has not left it has made me curious but not curious enough to pull the engine back out as enthusiasm is back to zero. I have a few mechanic buddies they are stumped as well as a good buddy who has had lt1 cars for 15 years. Anybody got any ideas. Been reading lots of forum posts with the same problem but nobody has figured out the problem or at least not come back and said what fixed it. Including people who have had a fresh rebuild only to have a pressure drop under load, rebuild the engine with all new bearings,plugs, and pump to have the same issue come back. I have a feeling this car is just cursed.
Is the car fully warmed up in that vid? Oil takes 3x as long to heat up compared to coolant. If it is then your oil pressure is wayyyyy too high. 40 psi at idle is up there.
Are you running a HV pump on a motor with stockish clearances? If the pump is nearly at the relief psi @ idle then going up in rpm will only lead to cavitation, hence the pressure drop. No windage tray also makes it easier to aerate your oil because the crankcase turns into a big frothy mess, which in turn causes more cavitation. Running a HV pump is also a good way to toast your drive gear.
The relief spring looks like the stock one on the gauge which I think is 58 psi.
If so, watch this....the fix was a 20185 Moroso Pan and a Canton pickup 20-013. I think the pickup did more for it than the pan, but as I did both at the same time...I can't be sure.
Is the car fully warmed up in that vid? Oil takes 3x as long to heat up compared to coolant. If it is then your oil pressure is wayyyyy too high.
Are you running a HV pump on a motor with nearly stock clearances? If the pump is nearly at the relief psi @ idle then going up in rpm will only lead to cavitation, hence the pressure drop. No windage tray also makes it easier to aerate your oil because the crankcase turns into a big frothy mess, which in turn causes more cavitation. Running a HV pump is also a good way to toast your drive gear.
The relief spring looks like the stock one on the gauge which I think is 58 psi.
Engine was warmed up. Stock GM pump for a lt1 with the screen 3/8 of inch from the pan. I think the gauge is reading a little high compared to the mechanical. However the drops have copied when using the mechanical gauge.
If so, watch this....the fix was a 20185 Moroso Pan and a Canton pickup 20-013. I think the pickup did more for it than the pan, but as I did both at the same time...I can't be sure. Solved LT1 Oil Pressure Dropping issue at WOT! - YouTube
Make sure you don't have a HV pump. There is no need to run them on a street driven LT1.
No High Volume Pump. I only use factory style pump. This one was ordered from gm with a gm pickup.
However still does not explain the issue of now oil flow in the pushrods and rockers. They are almost dry after a drive today.
One I ordered right from Gm Parts Direct. Was the same one that came off the engine. I could go snap a picture of that one if you want. Part number was a M155
So your pressure never gets below high 30s at a hot idle?
What's in the video up top looks like a windage issue to me.
Yep, after looking last night pump is confirmed to be a standard volume pump. I guess the electronic gauge is reading high. Could be a windage issue. Still stuck with this problem and oil not going to the top of the head.
Originally Posted by ******
96
when the motor was rebuilt, was the ball put back in the rear oil passage?
I never took the heads off the engine. I only had the main caps off the engine with it upside down. Pretty much I took the rockers off and pushed the pistons down. This way I saved money on a whole rebuild.
Originally Posted by Catmaigne
^^^ Good point, that would bypass the oil filter entirely
Again unless it has fallen out I am pretty sure it was still there. Can't confirm it tho. Granted I must have missed it in the lt1 rebuild book. It should be there. Last filter had oil in it and it went on empty since I was going to prime the system.
The ball won't just fall out when you tear the motor down as it is a slight press fit and needs to be knocked out with a brass drift and put back in that way. Without it the oil wont go through filter I believe so you need to change it more frequently but I don't think it results in low oil pressure if not in
Have you checked the oil pan to oil pick up clearance? Had a LS Vette having the same problem and we found the pick up was only 1/8" from the pan. Put clay on pick up and set the pan on. Remove pan and measure how thick the clay is. Should be around 3/8".
If anything, I think the oil pressure would be higher without the ball in place. I still think the pressure drop is from your lack of windage tray but it's strange that you're not getting any oil to the top end. If there was some sort of obstruction around the rear cam bearing I could see it, but I'd imagine you would have lost a bearing by now.
What kind of preload are you running on the lifters?
This is a generic sbc diagram but the system should be nearly the same.
If anything, I think the oil pressure would be higher without the ball in place. I still think the pressure drop is from your lack of windage tray but it's strange that you're not getting any oil to the top end. If there was some sort of obstruction around the rear cam bearing I could see it, but I'd imagine you would have lost a bearing by now.
What kind of preload are you running on the lifters?
This is a generic sbc diagram but the system should be nearly the same.
I would be thinking the same as the crankshaft is the last thing to get oiled. Starting to think it could be a windage issue. When I got this engine it had a stock oil pan with no windage tray. The corner had some light damage so I used my stock oil pan from my other engine. However If there was a blockage you would think a bearing would be dead by now. You would think the old owner was having this issue as well. Nothing on his forum about it so either he never noticed or this problem started in the accident?
When I had the engine apart the timing chain was off the engine. When I went to reset the pulleys with the rockers loose the cam was kinda hard to get spinning. With the timing gear pulley on the cam took a slight grab to get it going. However after that everything was super smooth. Cam would rotate with one finger. Maybe one of the bearings spun with that initial rotation. I am not talking about a big amount of force. My initial though was a rocker may not have been backed off all the way creating a slight pressure. Pretty sure it spun backwards then I checked all the rockers and found a few that still had pressure. Once those were backed off even more the cam would spin freely with one finger on the timing gear.
As for the rockers this was the second time with these comp pro mags. I used to run the GM lt4 hot cam rockers on the cc503 cam. For those I used 5/16 of a turn and they were always happy. On these Comp pro mag I herd to use about 1/8th of a turn. When I started it the first time they were kinda loud. I have moved to about 3/16 of a turn and they are all much better even with no oil. They still have a little side to side movement when cold.
If you have no rockers making very loud tapping sounds, I would think that the the oil pressure is fine to the lifters....or at least there is enough to pressurize them.
As for no oil to the rockers, can you take the drivers valve cover off(make a cardboard shield to prevent oil from going everywhere), start the engine, let it idle, and see how much oil is going to the top end as it idles....maybe video that too.
I'm assuming this is a 96 per your name. Where did you put the mechanical gauge? In the port around the oil filter? If so, if both the mechanical and in the car gauge agree, then the pressure is being lost before the one at the lowest point. Which, to me, would present as a feed issue.
If you can, get a video of the pressure on WOT through first and second gears taking the engine to around max rpm for your motor. I'd like to see what the pressure does....unless it's so bad you are worried about hurting the motor.
If you rev it to ~5000 at idle(without the car moving) does the pressure drop?
The check ball is something for sure you want to make sure is present. The LT1/LT4 rebuild books makes mention that you will have a massive leak at the rear main cap if it's not present....if that's the case...I'm not certain.
My oil pressure issues only showed up at WOT on hard acceleration. Yours seems to be more concerning.
I use 1/2 turn on my Pro Mags with stock lifters. No issues.
If you have no rockers making very loud tapping sounds, I would think that the the oil pressure is fine to the lifters....or at least there is enough to pressurize them.
As for no oil to the rockers, can you take the drivers valve cover off(make a cardboard shield to prevent oil from going everywhere), start the engine, let it idle, and see how much oil is going to the top end as it idles....maybe video that too.
I'm assuming this is a 96 per your name. Where did you put the mechanical gauge? In the port around the oil filter? If so, and both the mechanical and gauge in the car agree, then the pressure is being lost before the one at the lowest point. Which, to me, would present as a feed issue.
If you can, get a video of the pressure on WOT through first and second gears taking the engine to around max rpm for your motor. I'd like to see what the pressure does....unless it's so bad you are worried about hurting the motor.
If you rev it to ~5000 at idle(without the car moving) does the pressure drop?
The check ball is something for sure you want to make sure is present. The LT1/LT4 rebuild books makes mention that you will have a massive leak at the rear main cap if it's not present.
My oil pressure issues only showed up at WOT on hard acceleration. Yours seems to be more concerning.
I use 1/2 turn on my Pro Mags with stock lifters. No issues.
Ill start at the top. Lifters are getting some oil they are not loud like they are out of oil but they are loud enough that they are not getting enough oil. There is flow but not enough to make them happy. Ill make a video of that tomorrow.
Mechanical gauge went in where the electronic sending unit goes. This way I could drive the car with the gauge on the windshield to watch it. The hose is sort that it would not make it from the lower port. It has always done what the electronic has done. Dropped at wot. Ill make a video tomorrow.
Ill take the car out tomorrow with the mechanical gauge. Ill run as much as I fell comfortable with. If the pressure drops enough I will shut down early.
As for the 5000 rpm. If the car is sitting I can bring the rpm up and hold it with no issues. This video was up earlier in the post here it is again.
12-10-2015, 04:34 PM
Oil pressure problems Again 
