oil pressure
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Junior User
Joined: Oct 2004
Posts: 59
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From: newberry mi
oil pressure
helo just freshly rebuilt a 302 and am having some problems, i installed a mellings high vlume oil pump in it and when i first started the motor up it jumped to 60psi oil pressure. after a while it would idle down to 20psi for oil pressure. day 2 i started it up and only went to 40 cold and would idle at 10 psi. day 3 cold would only go to 30 psi cold and drops right off to 1-2 pounds at idle. when i did this motor i replaced the cam but not the cam bearings.(did not know how) and now once it warms up has a small knock at 2500 rpm's and power seems to drop off and will not build oil presure above 10psi so i parked it. my question is, is my oil pump going weak or am i gonna have to change those cam bearings?
if i do have to change the cam bearings how would i go about it, and also how would i test the oil puimp to see if it is failing. thanks much... sam
if i do have to change the cam bearings how would i go about it, and also how would i test the oil puimp to see if it is failing. thanks much... sam
Senior User
Joined: Oct 2005
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Did you pull the oil pan and check the screen on the bottom of the pick up tube? Sounds like the screen may be clogging up. Did you use a moly based assembly lube? Remember that molybdenum is a solid, and if there is an excessive amount, it could clog the screen. This happened to a friend of mine after a Pontiac ram air IV engine rebuild. I would check the oil pick up screen before I did anything else. Hopefully that is your problem, and it's a simple, cheap fix. Good luck!
Hotshot
Joined: Jul 2002
Posts: 14,285
Likes: 12
From: Bend,OR
yep not replaceing those bearings was bad idea. also there is no reason to run a hi volume pump on a stock motor build. did you install new lifters? what about the rest of the motor anything else get reused? i would remove that oil pump and install a stock one first. also did you do the 2000rpm cam break in on first start up? are you using a mechanical oil gauge?
need to know what rig, year your dealing with as well
need to know what rig, year your dealing with as well
Senior User
Joined: Jun 2004
Posts: 353
Likes: 3
From: Mid-Missouri
I agree with Kemicalburns.
Don't really need the HV Pump in a stock motor. The bearing clearances on a stock motor are pretty tight for a HV PUMP. The relief valve could possibly have been damaged by the backpressure experienced during the initial run.
If you were running 1-2 PSI like you say, you probably would have heard some strange noises. Probably did some damage to the new cam and possibly finished off the bearings.
With a gauge you should have 40-60 PSI at 2000 RPM after the motor is good and warm with a mechanical guage.
Minimum oil pressure to operate and not cause significant damage is suppose to be 8 PSI idling. I'd be concerned with any motor that had only 8 PSI oil pressure.
Don't really need the HV Pump in a stock motor. The bearing clearances on a stock motor are pretty tight for a HV PUMP. The relief valve could possibly have been damaged by the backpressure experienced during the initial run.
If you were running 1-2 PSI like you say, you probably would have heard some strange noises. Probably did some damage to the new cam and possibly finished off the bearings.
With a gauge you should have 40-60 PSI at 2000 RPM after the motor is good and warm with a mechanical guage.
Minimum oil pressure to operate and not cause significant damage is suppose to be 8 PSI idling. I'd be concerned with any motor that had only 8 PSI oil pressure.
Last edited by lmadore; Oct 25, 2005 at 10:38 AM.
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Junior User
Joined: Oct 2004
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From: newberry mi
i did install new lifters in the motor and the motor is out o a 85 ford thunderbird. the only thing i reused was crank, pistons, oil pickup tube and cam bearings. pulled the pan off today, the oil was grey. particles in it, so gonna have to pull the motor once again and re bearing the whole shot. hopefully the cam will be allright, crank stil looks good, no scor marks or grooves in it i beleieve i stoped the motor soon enough. on the main bearing just a couple spots where it was down to the brass, but very very little. looks like gonna do it again and do it right this time. also btw anyt tricks to installing them pesky cam bearing i would appreciate it much.. thanks again
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Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
just take it to a machine shop for the cam bearings. about 30.00 or so for labor. did you plastigauge th engine and check all the clearances?
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Cargo Master
Joined: Jan 2004
Posts: 2,512
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From: Cook Forest and Irwin PA
I dunno, the bearing clearance is whatever you set it to be.....if the original motor had excessive clearance than a cheap rebuild with the same original size or +.001 bearings might come close to original. IF you had the crank ground then you would have plastigaged the journals when selecting the oversize.
with suspect clearance, I would actually recommend a hivol pump over a high pressure pump. the oil bleeddown with over size clearance needs to be compensated for.
with suspect clearance, I would actually recommend a hivol pump over a high pressure pump. the oil bleeddown with over size clearance needs to be compensated for.