Oil pressure problem - new engine rebuild
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Oil pressure problem - new engine rebuild I have a lm7 that I just rebuilt. Installed mild cam, springs, hardened pushrods and port and polished heads. I put it all back together and when I go to prime the engine before I start it I have only 1.25psi oil pressure. The cranked the engine 4 or 5 times to build the oil pressure but I'm not getting anything. Can some one help me on were I went wrong. Thank you.
Sometimes they are just slow to prime.
Since it's already together, try filling the oil filter, then remove the oil pressure sending unit out at the back of the block and pour oil in there.
This at least fills the passages.
I did all this and it finally primed to 10 psi. I fired it up and it immediately went to 40 plus psi.
Since it's already together, try filling the oil filter, then remove the oil pressure sending unit out at the back of the block and pour oil in there.
This at least fills the passages.
I did all this and it finally primed to 10 psi. I fired it up and it immediately went to 40 plus psi.
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So I did fill the filter and the sending unit with oil and I pulled the plugs and tried to prime it and still nothing. Any other ideas you have for me that I can try before I dismantel the engine back again?
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When you say rebuilt did you completely dismantle the motor or did you just do the heads, cam, etc.? If you left the bottom end alone then I would think you could have possibly damaged the oil pickup o-ring. I would probably briefly fire it and see if it builds oil pressure in 10 seconds or so.
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I took the oil pan and the pickup tube complete off and reinstalled them. I went back today and took them off again in the mornings just to make sure the o-ring was not pinch or something. Everything down there is where it should be. Nothing is out of place.
On The Tree
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If you didn't use the prime port there in the front of your block to the right of the timing over, to prime the oil pump, that would be a good place to start, as just filling the filter and oiling the oil sending unit hole, because it doesn't fill the oil galleys in front of the filter that leads to the oil pump.. so it isn't enough lots of times..
It wasn't enough for me.. but as soon as i filled the prime port there in the front of the engine, the oil pressure jumped to 50+ right off the first few cranks with out starting the engine.. its going to be hard to fill once the engine is in the vehicle but.. i think you can do it.. just make sure to get it completely full let it burp a few good times before your ok with it being full enough..
Other than that, maybe barbell or the wrong pickup tube O ring size or even if reused old one, and if you reused the cam retainer plate, even if it looked good, or if you didnt clean the matting surface on the block really good, it can leak, even so by just reusing the old one.. as i tried 3 old ones all looked fine, but all leaked like a water fall out of the top between the bolts...
But yeah, try the prime port there.. i think it should work.. i hope so neways.. sure hope its something simple man
peace
It wasn't enough for me.. but as soon as i filled the prime port there in the front of the engine, the oil pressure jumped to 50+ right off the first few cranks with out starting the engine.. its going to be hard to fill once the engine is in the vehicle but.. i think you can do it.. just make sure to get it completely full let it burp a few good times before your ok with it being full enough..
Other than that, maybe barbell or the wrong pickup tube O ring size or even if reused old one, and if you reused the cam retainer plate, even if it looked good, or if you didnt clean the matting surface on the block really good, it can leak, even so by just reusing the old one.. as i tried 3 old ones all looked fine, but all leaked like a water fall out of the top between the bolts...
But yeah, try the prime port there.. i think it should work.. i hope so neways.. sure hope its something simple man
peace 
Did you put a new O-ring on the pickup tube or use the old one? I've fixed trucks with low or no oil pressure with a new ring. The o-rings shrink and harden and won't work even if not pinched.
You are doing way more damage trying to prime it with the starter than just starting it and letting it run.
The best way to prime it is pump the oil into it with pressure.
Tim
The best way to prime it is pump the oil into it with pressure.
Tim
On The Tree
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Because iv done it both ways and i got way more damage by starting it and letting it run.. if doesn't prime up by turning the engine over with the starter, how is letting it run at no oil pressure with combustion going to be better for it... i was able to get 50 something psi at only 125 or so rpms
See time count around 4 mins
But yeah unlike the engine i just started and let run, it didn't ever build pressure.. so the more damage was obviously done by starting and letting run with no oil pressure .. i wouldn't risk damaging your bearings by starting it and hoping it builds pressure ..
Edit: Now on the engine i started and let run to get oil pressure though it didn't get pressure the first or second or even 3rd start, i said O WELL and started it a 4th time and i hit the rev limiter and let it ride, then about 30 sec later, she got pressure.. ha lol though it had a O ring problem had to take the pan off, reused the same oil, after starting the 5th time it had pressure.. 60+idle, 80+WOT
I drove it about 100miles changed the oil and it was FLAKY BIG TIME.. looked like glitter.. and even the next oil change at 300 miles, but that engine seen 6700rpms for the first year and 6200 for the next 4 years 20,000 miles..
I will be making a video soon of that engine and what the bearings look like..
But yeah neways hope this doesn't offend and hope it helps ev1 out ...
peace Last edited by the404man; Jan 3, 2016 at 04:58 PM.
Cranking on it for 3 min or it running for 1 with no pressure the damage is done. My point is cranking on it is harder that just starting it. If built correctly it will have oil pressure. 125 rpm of the starter is not always enough to prime one. Pressure priming is what should be done and it within 15 seconds it does not have oil pressure should be shut off.
Tim
Tim
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If you didn't use the prime port there in the front of your block to the right of the timing over, to prime the oil pump, that would be a good place to start, as just filling the filter and oiling the oil sending unit hole, because it doesn't fill the oil galleys in front of the filter that leads to the oil pump.. so it isn't enough lots of times..
It wasn't enough for me.. but as soon as i filled the prime port there in the front of the engine, the oil pressure jumped to 50+ right off the first few cranks with out starting the engine.. its going to be hard to fill once the engine is in the vehicle but.. i think you can do it.. just make sure to get it completely full let it burp a few good times before your ok with it being full enough..
Other than that, maybe barbell or the wrong pickup tube O ring size or even if reused old one, and if you reused the cam retainer plate, even if it looked good, or if you didnt clean the matting surface on the block really good, it can leak, even so by just reusing the old one.. as i tried 3 old ones all looked fine, but all leaked like a water fall out of the top between the bolts...
But yeah, try the prime port there.. i think it should work.. i hope so neways.. sure hope its something simple man peace
It wasn't enough for me.. but as soon as i filled the prime port there in the front of the engine, the oil pressure jumped to 50+ right off the first few cranks with out starting the engine.. its going to be hard to fill once the engine is in the vehicle but.. i think you can do it.. just make sure to get it completely full let it burp a few good times before your ok with it being full enough..
Other than that, maybe barbell or the wrong pickup tube O ring size or even if reused old one, and if you reused the cam retainer plate, even if it looked good, or if you didnt clean the matting surface on the block really good, it can leak, even so by just reusing the old one.. as i tried 3 old ones all looked fine, but all leaked like a water fall out of the top between the bolts...
But yeah, try the prime port there.. i think it should work.. i hope so neways.. sure hope its something simple man
peace On The Tree
Joined: Jun 2012
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Cranking on it for 3 min or it running for 1 with no pressure the damage is done. My point is cranking on it is harder that just starting it. If built correctly it will have oil pressure. 125 rpm of the starter is not always enough to prime one. Pressure priming is what should be done and it within 15 seconds it does not have oil pressure should be shut off.
Tim
Tim
peace man I miss spoke, and i took what you said before by saying to "starting it and letting it run" wrongly.. sorry man
guess anyone with common sense would know if it didn't get pressure to shut it off .. i wasn't thinking correctly .. haha totally thought you meant to start it and just let it run even if no pressure lol .. i should have thought about what you said a little longer before replying ..
but yeah
peace Tim On The Tree
Joined: Jun 2012
Posts: 122
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Yeah i so wouldn't be happy with 25, but it is pressure.. i would think it would be fine to start and let run now for a bit longer to see if it increases..
im not so learned on superchargers don't they require oil pressure from the engine or is it a sealed unit...?
but yeah if it does get oiled from the engine, maybe air still needs to get pushed out..
I will say, if you do decide 25psi is ok, once your up to temp and all, check your dip stick see if there are bubbles on it, if not and you then decide to run with it at 25psi, after driving hitting the higher rpms, check for bubbles again, then if so you either have a O ring problem or even the cam retainer plate.. not so sure about the bubbles for the retainer plate leak, but the retainer plate also could very well cause low pressure...
Really hope things work out
peace man