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Got the oil pump out today. Here are some pics of it: Oil Pump with cover removed
Oil pump with impeller removed
I couldn't really see anything wrong with it. There was no grit (or red RTV) evident in it. I removed the spring from the bypass valve. It looked ok, the piston seemed to move freely. The only thing I can think of is that the piston may not be sealing properly. I don't know how to test it.
I think the best course of action is to replace the oil pump. Anyone have any suggestions on a resonably priced replacement?
My main concern is that a new oil pump may not solve the problem.
I think most of us have a budget. I always install a new barbell, but that's me. I'm wondering if the gerotor gears are installed exactly as they were removed? IIRC, they can be installed either way, but will only work correctly if installed the correct way. @Che70velle would know this answer for sure. Best of luck to you.....
Yeah, that pump gerotor looks good. No scoring, right?
I always try to replace the barbell as well, but as far as I knew, that one just directs oil flow into the oil filter. Even if you omit it, you would have pressure, just oil won't get filtered.
I wish there was a way to bench test the engine by feeding oil to it externally. I had never wondered how that could be done. I guess with a dry sump system? I'm not really sure how those work and pretty sure all of that stuff is expensive to only use as a test here.
This one's making my head hurt, I was thinking maybe there could be a bigger chunk of debris Left from the machine shop stuck down in the main oil passage or something like that or what if some of the bearings were not clocked properly? because scarily it is looking like a new oil pump may not solve this issue these oil pumps are incredibly simple. Doesn't the regulator only limit the pressure?. There's another guy and another thread that's almost got a hundred PSI oil pressure lol. I agree the RTV on there is a bad idea but still I've had spun cam bearings and ripped o-rings In the same engine and that still gave 10-15 psi at idle so I really think there's something else going on here
The (new) cam bearings and cam were reassembled by the engine shop. So I've got to assume they did it right (the guy there is very experienced and knowledgable). I rebuild the rest. I can't see anything obviously wrong with the main bearing. I'll inspect them closely today and maybe take off one or two of the caps to check further. But I made sure I had all the oil holes lined up, so unless one has spun, I don't think its a problem with the bearings.
I haven't checked the oil filter yet, should do that next. The barbell looks like its in the correct position - you can see it through the two holes at the bottom of the block. The front of the engine looks fine. The new double row timing chain seems to have just the right amount of slack (I was worried about it when I put it on as it was very tight, but the engine shop assured me it would loosen up which it has).
I'll pull the rocker covers off and take at the rockers and pushrods. I had used new pushrods which are slightly shorter than stock, due to the skimming of the heads and the new LS7 lifters which are slightly longer. I've got 7.35" in there as opposed to the 7.4" stock pushrods. I think these are just on the edge of being too long, as the turns from lash were about 1 and 3/4 for most of them (should be between 1/2 and 1 and 1/2 as I understand). Engine shop said should be ok as on occasions they've had engines that can go up to 2 turns without any issues.
Yeah, that pump gerotor looks good. No scoring, right?
I always try to replace the barbell as well, but as far as I knew, that one just directs oil flow into the oil filter. Even if you omit it, you would have pressure, just oil won't get filtered.
I wish there was a way to bench test the engine by feeding oil to it externally. I had never wondered how that could be done. I guess with a dry sump system? I'm not really sure how those work and pretty sure all of that stuff is expensive to only use as a test here.
Just to clarify here, if the barbell is missing, the engine won’t make much more than 20psi at wot. At idle it would virtually read zero. The barbell does direct oil to the filter, but it also has an o-ring on the rear side of it, and it directs oil up the circuit to the OPS, and onto the rest of the circuit…cam bearings, then crank, then rods. Lifters get oiled along the way to cam bearings, which direct the oil up top. Said all of that to say that the o-ring on the barbell seals the oil circuit. If it’s out of the block, oil pressure is extremely low…to zero. The only reason that pressure would even barely register, is because the OPS is on the same side of the block as the barbell…directly above it in fact.
There was a guy on here way back that had ERL sleeve him a block, which he went to a 434 with. Big money build. The gentleman never noticed that ERL removed the barbell. He assembled the engine himself, and when he fired it, oil pressure was zeroish at idle and when revved it would blip up a tad. Long story short, he drove the car hoping that the 20ish lbs of pressure would suffice at WOT. It did not. Pulled it out, tore it down, and after advice here, realized the barbell was missing. ERL ended up covering half of the repair price after much back and forth, he said-she said business. It was a mess. The engine…if I am remembering correctly…had a pretty hot oil pump. High volume, high pressure deal, which is likely why he saw the 20ish psi at WOT. With a stock pump, I don’t think it would have made hardly any pressure at WOT.
I think most of us have a budget. I always install a new barbell, but that's me. I'm wondering if the gerotor gears are installed exactly as they were removed? IIRC, they can be installed either way, but will only work correctly if installed the correct way. @Che70velle would know this answer for sure. Best of luck to you.....
Ive had the rotors out of many pumps…even had them coated. You can see the indicator mark…that little dot…that faces out. Some have them, some don’t. Clocking the two together doesn’t matter, as they spin independently of each other at different rpm. So…dots go outward, and if no dots then it doesn’t matter. Put some oil in there before putting the cover back on to help it prime.
The barbell is definitely in there. I distinctly recall inserting it and noticing that the o-ring made a tight seal with the block. Is there any reason that it would get pushed out ?(due to pressure, etc)
The barbell is definitely in there. I distinctly recall inserting it and noticing that the o-ring made a tight seal with the block. Is there any reason that it would get pushed out ?(due to pressure, etc)
it can’t get pushed out. The rear cover is roughly 1/8” behind it, and the GM engineers allowed for this by putting the o-ring just over 1/8” from the rear.
The barbell is definitely in there. I distinctly recall inserting it and noticing that the o-ring made a tight seal with the block. Is there any reason that it would get pushed out ?(due to pressure, etc)
No. I still believe it is a pickup side issue somewhere. I seem to remember hearing that some LS1s had a problem with the pickup tube cracking at the ear, where the mounting ear is welded to the tube that mounts it to the engine. Your situation is puzzling. Almost like a pickup screen being plugged. When you re-prime, it pushes the gunk off the screen, and it works again......For awhile. I'm not saying that is it, but it kinda acts that way. IDK, this is an unusual problem. It has to be the intake side of the pump is sucking air somewhere. It would be interesting to dump another 4 qts of oil in there, and just let it idle. If the pressure comes up, then it's definitely on the pickup side somewhere.........
Any thoughts about a Melling M295 oil pump? I can get one at a good price. I've read that it has slightly higher pressure that the stock pump (+10psi).
I'm starting to think you are right. The fact that I reprime it and it gets pressure again suggests the pump is being starved for oil. I'm using a pressure sprayer to reprime the pump, and the oil quickly runs up to and out of the sender hole which suggests at lease in that part of the engine there is no blockage.
Has it been confirmed that the OPS is accurate? I know it’s very late to ask, but has that already been covered here? Was a mechanical gauge used to confirm? I’m simply too lazy to go look back…
I have an oil pressure gauge on the dash. I've checked it against the signal from the PCM. When there is pressure, the PCM generally reads around +10psi over the dash gauge. When the dash gauge reads 0, the PCM also reads 0.
BTW, the two times I have drained the engine oil since the rebuild, the color of the oil is rather dark. Its unusual as I've not done a lot of miles since I rebuilt it. Not sure if this is significant?
12-12-2023, 08:17 AM
