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Old 07-18-2012, 08:27 PM
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no oil pressure at idle

Hi all. I rielly need help.
350 small block just got it back from shop borred out 40 thousands.
10/10 grind on the crank.
and valve job completed.
I have 40 to 50 psi. when i throttle the gas and 20 psi at idle but 0 psi in gear at idle rpm is at 550.
I have changed out the oil filter due to being a fram filter. I am still breaking in the engine with 95 miles on it so far.
Is it the brteak in oil causing the no oil pressure?
I performed a plasti gage on crank and is .001 to .003
Any help sure would be great.

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Old 07-18-2012, 08:54 PM
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It still has oil pressure at idle otherwise it would have already let you know.
The problem is the gauge. Just about all gauges are not accurate below 10 psi, some as much as 20 psi.
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Old 07-18-2012, 11:03 PM
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no oil pressure at idle

I hooked up an external gauge and no differance. My son did have the wrong gasket on the oil filter adaptor which may have let the break in material reserculate back into the engine. Could of this caused me to loose pressure while I am breaking the engine in?? Damaging cam bearings and crank bearings
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Old 07-18-2012, 11:43 PM
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If that was the case, I'm sure you'd hear the death rattle...

Are the rockers noisy at idle, in gear?
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Old 07-19-2012, 12:22 AM
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no oil pressure at idle

Yes the rockers get louder the longer the gage is at 0... Buy no noise with oil pressure.. the cam and bearings are brand new. New oil pump, even checked that oil is flowing by spinning the shaft with the oil tube in a bucket of oil. After it sets for awhile the oil cools and then I run the engine till temp reaches 190 I have 40 psi at idle until the oil heats back up. Then back to 0 oil pressure.
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Old 07-19-2012, 05:43 AM
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Was the core plug installed under the rear main cap properly? Oil pickup installed in the oil pump ok? not leaking or sucking air? Could be too much main bearing clearances also. Its not your Fram filter.
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Old 07-19-2012, 07:49 AM
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Quote:
Originally Posted by Richiehd View Post
Was the core plug installed under the rear main cap properly? Oil pickup installed in the oil pump ok? not leaking or sucking air? Could be too much main bearing clearances also. Its not your Fram filter.
Leaving the core plug out has nothing to do with low oil pressure all it does is by pass the oil filter.

I have to ask since you wrote this leaving the core plug what do you think causes the low oil pressure ??????????????????
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Old 07-19-2012, 10:32 AM
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Quote:
Originally Posted by riderrich View Post
Yes the rockers get louder the longer the gage is at 0... Buy no noise with oil pressure.. the cam and bearings are brand new. New oil pump, even checked that oil is flowing by spinning the shaft with the oil tube in a bucket of oil. After it sets for awhile the oil cools and then I run the engine till temp reaches 190 I have 40 psi at idle until the oil heats back up. Then back to 0 oil pressure.
A few things to check off the top of my head:
• leaking/missing galley plugs at the front of the engine under the timing cover
• rear galley pipe plug leaking/missing
• distributor body is a too-loose fit to seal off the lifter galley crossover
• bearing oil clearances are too wide
• oil viscosity is too low
• oil pump bypass is hanging open

Quote:
I have to ask since you wrote this leaving the core plug what do you think causes the low oil pressure ??????????????????
Is the reason you posted just to try to make someone look bad? That info has been circulated since day one and can be found even on otherwise reputable sites and from sources that are otherwise trustworthy. That doesn't make it true that the oil pressure will be zero w/the plug left out- but it damn sure doesn't call for anyone trying to belittle anyone else for repeating it. A simple explanation would have been plenty. And maybe an answer to the original poster would have helped, too.

A diagram of the plug and measurements of its location so the block can be checked for the plug being in the right place is HERE. By examining the diagram, you can see that the oil pressure shouldn't be lost if the plug is left out.
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Old 07-19-2012, 11:04 AM
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I have seen such a pressure problem on a few occasions caused by the rear cam bearing not being installed all the way and exposing the groove in the journal.

The plug has nothing to do with pressure issues, just filtering.
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Old 07-19-2012, 11:58 PM
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no oil pressure at idle

Recieved what is called a wet bottle test tank... From the machine shop that did the workIt's a 5 gallon pressure tank with 2 quarts of oil in it. Connecting line goes to the oil sensor plug hole. I hooked up air from my air compressor and them removed my pan. The shop told me to watch where all the oil is coming from to see were the leak is. I found all the oil coming from the rear main cam bearing. Had around 80 psi on the tank so I am sure it is the rear main cam bearing not installed correctly.... I sure hope the machine shop will fix this issue for me for free. I paid almost 2 grand for this rebuild so far.
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Old 07-20-2012, 06:22 AM
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I was not sure if the plug under the rear main would lose pressure or just by pass the filtering, I have been corrected. However I do know too much clearance will affect oil pressure especially when hot. Sounds like the original poster did the right thing. I would still check the oil pump and see what pressure the pump is capable of. I have seen bypass valves hung up, pickups fall off and pumps break off the rear main cap, so I am not new to this game.
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Old 07-20-2012, 06:22 AM
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Quote:
Originally Posted by riderrich View Post
Recieved what is called a wet bottle test tank... From the machine shop that did the workIt's a 5 gallon pressure tank with 2 quarts of oil in it. Connecting line goes to the oil sensor plug hole. I hooked up air from my air compressor and them removed my pan. The shop told me to watch where all the oil is coming from to see were the leak is. I found all the oil coming from the rear main cam bearing. Had around 80 psi on the tank so I am sure it is the rear main cam bearing not installed correctly.... I sure hope the machine shop will fix this issue for me for free. I paid almost 2 grand for this rebuild so far.
What may have happened (and is harder to see but easier to feel, and in my experience happens as often if not more so than an incorrectly positioned rear cam bearing) is a #3 or #4 cam bearing is installed in the rear position. Which then would beg the question, what happened to the #5 bearing- is it in the wrong spot too? If you end up pulling the cam, be sure to see if the #3 or #4 cam bearing has been shaved down/clearanced. If you see that, it's a pretty good chance that it'll be your rear bearing.

It never ceases to amaze me how the simplest things are still being botched by shops who charge guys good money for their "expertise". I realize that 'stuff' happens, but come on.

OT- Recently, someone here at Hotrodders said they never measure the cranks they get back from the shop. I replied that I always check everything I can. And it's examples like THIS that is the reason why I say what I said and do what I do!
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Old 07-20-2012, 06:27 AM
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Originally Posted by cobalt327 View Post
Is the reason you posted just to try to make someone look bad? That info has been circulated since day one and can be found even on otherwise reputable sites and from sources that are otherwise trustworthy. That doesn't make it true that the oil pressure will be zero w/the plug left out- but it damn sure doesn't call for anyone trying to belittle anyone else for repeating it. A simple explanation would have been plenty. And maybe an answer to the original poster would have helped, too.

A diagram of the plug and measurements of its location so the block can be checked for the plug being in the right place is HERE. By examining the diagram, you can see that the oil pressure shouldn't be lost if the plug is left out.
Not at all but some one posts this info they should know what they are talking about. Just checking to see if poster could back up what he was saying. Thats all.

Some people make up things to post and this might be a good example!!!
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Old 07-20-2012, 06:48 AM
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What I'm saying is this info has been circulating for ages. It appears in reputable publications- someone said Lingenfelter has repeated it although I don't own his books. So I do not think he "made up" anything. Hell, the same info is repeated in another thread "350 chevy, oil pressure drops to zero when warm", running the same time as this thread!

In any event, hopefully good informative posts like by oldbogie, on the other thread, the following diagram (from here, feel free to add to the page or edit as you see fit), and even your posts will help dispel this myth:


Last edited by cobalt327; 07-20-2012 at 07:04 AM.
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Old 07-20-2012, 03:49 PM
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Quote:
Originally Posted by cobalt327 View Post
What I'm saying is this info has been circulating for ages. It appears in reputable publications- someone said Lingenfelter has repeated it although I don't own his books. So I do not think he "made up" anything. Hell, the same info is repeated in another thread "350 chevy, oil pressure drops to zero when warm", running the same time as this thread!

In any event, hopefully good informative posts like by oldbogie, on the other thread, the following diagram (from here, feel free to add to the page or edit as you see fit), and even your posts will help dispel this myth:

If you believe John that kind of proves your just book reader and really don't know how a SBC oiling system works LOL.

CAN YOU TELL WHY YOU WOULD LOOSE OIL PRESSURE WITH OUT THE PLUG BEING INSTALLED AND WHERE DOES THE OIL BLEED OFF.

Here is a good post about John Lingenfelter if you read this John is wrong about the plug under the rear cap.

PLUG UNDER REAR CAP • Speed Talk
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