New Rebuild, Low Oil Pressure
#1
New Rebuild, Low Oil Pressure
I recently rebuilt my 2 bolt 350 sbc. By rebuilt I mean crank honed, new bearings, new cam, new bearings, new pistons/rings, new heads, new oil pump, new lifters, and new gaskets all around. My gauge is only indicating 4-7 psi at idle though, and only going up a couple psi per thousand rpm's. It's only been ran for ~4-5 minutes. The gauge was displaying 80psi before the swap, but I think it wasn't connected or something weird like that. Any ideas? This is with 5w-30 oil and a standard pressure pump.
#2
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Car: 1991 GTA Purple of all colors
Engine: 350
Transmission: 4L60E
Axle/Gears: Crappy 3.23
Re: New Rebuild, Low Oil Pressure
Rule of thumb, 10PSI per 1 thousand rpm's. Drive the car at 3500-4K rpms and see if the gauge shows 35-40PSI. If it is lower the bearing clearances might be high or the oil pump screen is clogged. Did you run the engine for about 20 minutes at 2K rpms? After you do that you have to drain the oil and refill with fresh oil then run it for about 1500 miles and then change it again.
#3
Re: New Rebuild, Low Oil Pressure
I haven't done the 20 minutes yet because I was afraid I was going to hurt something. Oil is definitely flowing as I pre lubed the engine and saw oil coming out cleanly and steadily at a good rate.
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Car: 1991 GTA Purple of all colors
Engine: 350
Transmission: 4L60E
Axle/Gears: Crappy 3.23
Re: New Rebuild, Low Oil Pressure
On a fresh rebuild you will have all the assembly lube; which in itself is very thick; metal from parts breaking in, e.t.c When you 1st fire it up you should run it at about 15-2K RPM's to start the initial breakin then follow the other steps.
#6
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Re: New Rebuild, Low Oil Pressure
Possibly break in lube jammed up in the sending unit of the oil pressure gauge.
#7
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Car: 14 scion tc/91 camaro rs
Engine: 2.5/ 360 pooch
Transmission: 6spd man/th350
Axle/Gears: na/2.73
Re: New Rebuild, Low Oil Pressure
Surely you dont want to break in an engine with low oil pressure? Did the block have anywork done? If so someone could of taken the plugs out on the front of the motor that are behind the cam gear.
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#8
Re: New Rebuild, Low Oil Pressure
It was bored and cleaned. I got the one under the rear main cap and forgot the 1/4npt plugs when I prelubed and oil shot across my garage but I put those in before it went in the actual car.
#9
Re: New Rebuild, Low Oil Pressure
By the way, I did use a LOT of assembly lube. All journals were lubed, 2 packets of cam break in lube for cam+lifters, bottle of zddp additive, piston walls, etc.
#10
Re: New Rebuild, Low Oil Pressure
Which oil pump did you use??. Standard,high volume,high pressure??. Oil pressure is normally a derivative of the bearings,oil pump,pressure relief valve. Did you check the clearances during assembly??. You said the mains are line honed??. Not line bored??. Where the main caps cut to restore them??. Why where the mains machined in the first place??. Where they out of round??. If so,was the crank turned also??. Did you step torque the mains and did they seat correctly on the parting line??. Did you do the same for the rods??. What was the torque value you used for the mains and rods??. What brand name bearings did you buy??. Did you rife brush clean the passages??. A important fact during oil priming a engine is you want to prime it so the drill motor bogs down only twice then stop right after. Once to fill the oil pump and once to pressurize the oil passages to prevent a "dry start". Otherwise you could wash out the assembly lube. The 2500 rpm break-in at 20 minutes is mainly for a cam break-in on flat tappet cams. If it is a roller it isn't as important. Varying the speeds you drive at over time helps set the rings. Don't run it at a consent speed for a long time. If those rings are chrome rings it can take a long time for them to break-in. Did you check the ring end gap??. On a standard rebuild you wouldn't normally check each one,but aleast spot check randomly. The same for piston skirt to wall clearances. How did the walls measure??. Out of round??. Honed??.
Yes,I know it is a long bucket check list. But all important things to consider.
Yes,I know it is a long bucket check list. But all important things to consider.
#11
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Car: 14 scion tc/91 camaro rs
Engine: 2.5/ 360 pooch
Transmission: 6spd man/th350
Axle/Gears: na/2.73
Re: New Rebuild, Low Oil Pressure
None of that will affect oil pressure. Did you get the oil pickup tube pressed in all the way? If so then tou have a bad oil pump or your bearings are wrong. Recheck oil pressure with a mechanical gauge.
#12
Re: New Rebuild, Low Oil Pressure
So I finally got around to pulling the pan after I double checked the low reading. Oil sump is on firmly, and the pump is brand new. The rods, however seem to move horizontally on the crank until it hits the counter-weight or the other rod. Is this normal? The machine shop who turned the crank turned it 10/10, so I bought 10/10 bearings. The crank was already 10/10, the shop didn't mean to say it was an additional .010, do you think?
#13
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Car: 14 scion tc/91 camaro rs
Engine: 2.5/ 360 pooch
Transmission: 6spd man/th350
Axle/Gears: na/2.73
Re: New Rebuild, Low Oil Pressure
This is where id put a sad face.... ya thats not good, yes its very possible they ment an additional 10 under. So u would need 20 under bearings.
#14
Re: New Rebuild, Low Oil Pressure
Dannnggggiiitt. Yeah that's what I figured. Well, I know what i'm doing tomorrow Would the engine run with the oversized bearings though? And how can I check tolerances so this doesn't happen again? I've read mixed things everywhere ranging from plastigauge blows to jesus checks my bearing tolerances for me.
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Car: 14 scion tc/91 camaro rs
Engine: 2.5/ 360 pooch
Transmission: 6spd man/th350
Axle/Gears: na/2.73
Re: New Rebuild, Low Oil Pressure
Plastigauge, ya it sucks cause its time consuming. If youre not too considered with absolute accuracy is get digital dial caliper measure outside crank journals and then measure inside of bearings.
#18
Supreme Member
Re: New Rebuild, Low Oil Pressure
If I was running the machine shop I would of handed you the 20 over bearings when you where picking up your crank IMO.
#19
Supreme Member
Re: New Rebuild, Low Oil Pressure
Right, they could have been .010 too tight. That would have been much worse, don't you think? ;-)
#20
Re: New Rebuild, Low Oil Pressure
Heh...it's not so bad. Got all the rod bearings done, and end caps off, just need to put the main cap bearings on. I'll let you guys know how it turns out tomorrow...
#22
Re: New Rebuild, Low Oil Pressure
Sonofabitch...this is starting to really suck. Long story summarized, ended up breaking the harmonic balancer bolt turning over the engine and ended up pulling it. Measured and re-measured .010 and .020 bearing clearance. Got .0015 for both on the rods. .020 split the plastigage giving it that reading (expanded, reshrunk?). Crank seized with .020 bearings. The .010 bearings seem to have been correct. Now what caused the oil pressure do you guys think? There was some oil behind the distributer and dripping down the back...but where could that come from and or cause 40psi oil pressure drop? I know the cam bearings were installed correctly (centered upon the oil groove) with the hole in the correct position, etc. Any thoughts?
#23
Supreme Member
Re: New Rebuild, Low Oil Pressure
Well, there is a vertical oil galley hole on the rear rail just behind the intake. Most of the time GM put a sending unit right there. These cars don't always follow that, but the hole is there anyway. What do you have in your hole? That could make for 0 oil pressure if it were open, but there would be oil everywhere. Are you sure about your pressure gauge? A leaking sending unit is often a bad sending unit.
#24
Re: New Rebuild, Low Oil Pressure
Yup... definitely a sender unit there. I'm fairly confident about the oil, as the engine would stall when the oil got to 0 and the lifters would click as well
#25
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Car: 1989-92 FORMULA350 305 92 Hawkclone
Engine: 4++,350 & 305 CIs
Transmission: 700R4 4800 vig 18th700R4 t56 ZF6 T5
Axle/Gears: 3.70 9"ford alum chunk,dana44,9bolt
Re: New Rebuild, Low Oil Pressure
So I finally got around to pulling the pan after I double checked the low reading. Oil sump is on firmly, and the pump is brand new. The rods, however seem to move horizontally on the crank until it hits the counter-weight or the other rod. Is this normal? The machine shop who turned the crank turned it 10/10, so I bought 10/10 bearings. The crank was already 10/10, the shop didn't mean to say it was an additional .010, do you think?
The crank will slide back an forth in the mains also, thats called end play and its measured at the thrust bearing.
10/10 means 10 under on the rods and 10 under on the mains.
Always always check your clearances and write them all down in your engine assembly note book while building.
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Re: New Rebuild, Low Oil Pressure
Um, yes, 1/2" cup plugs, 3 locations. Be sure to stake them, and NO sealant on them. You can also drill small 0.040" holes in the two side ones to additionally lube the timing chain.
I hate to say this, but this is the first I read your thread and they are the first item that came to mind. Wish I had read it sooner. But you'll be up and running in no time.
RBob.
I hate to say this, but this is the first I read your thread and they are the first item that came to mind. Wish I had read it sooner. But you'll be up and running in no time.
RBob.
#29
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Car: 1989-92 FORMULA350 305 92 Hawkclone
Engine: 4++,350 & 305 CIs
Transmission: 700R4 4800 vig 18th700R4 t56 ZF6 T5
Axle/Gears: 3.70 9"ford alum chunk,dana44,9bolt
Re: New Rebuild, Low Oil Pressure
Wow... If your careful you can tap them for pipe plugs..
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