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Old 12-23-2008, 08:05 PM
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Oil.. how does it flow around an SBC?

Hi there,

I have an oil pressure problem on an SBC.. before I try and diagnose the issue and ask any specific questions I'd really like to understand how oil is pumped and managed inside the SBC.. I guess, any engine really.. but specifically the SBC.

If you know how it all fits together I'd really love a description of how the pump is driven, where the oil flows etc.. I know that removing the distributor provides an opportunity to prime the system and some information on how that is done would really be appreciated to.

With many thanks,

Dunc.
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Old 12-23-2008, 08:14 PM
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Quote:
Originally Posted by duncan_m
Hi there,

I have an oil pressure problem on an SBC.. before I try and diagnose the issue and ask any specific questions I'd really like to understand how oil is pumped and managed inside the SBC.. I guess, any engine really.. but specifically the SBC.

If you know how it all fits together I'd really love a description of how the pump is driven, where the oil flows etc.. I know that removing the distributor provides an opportunity to prime the system and some information on how that is done would really be appreciated to.

With many thanks,

Dunc.
What kind of oil pressure issue?
The pump is driven off the distributor by the cam gear. There's a shaft that fits between the dist and the pump.

The oil comes out of the pump, goes through the filter, hits the pressure switch, goes up to the lifter valley, heads, runs back down into the pan. that's pretty simplistic, but basically how it works.

Slap on a new filter just to see if the filter is the problem, just in case.

Cut the old one open see if there's metal in it.

Drain the oil pan and see if there's metal in the oil.

Take off the pressure switch and put in a mechanical gauge.

Report back.
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Old 12-23-2008, 08:22 PM
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Quote:
Originally Posted by Jsup
What kind of oil pressure issue?
The pump is driven off the distributor by the cam gear. There's a shaft that fits between the dist and the pump.

The oil comes out of the pump, goes through the filter, hits the pressure switch, goes up to the lifter valley, heads, runs back down into the pan. that's pretty simplistic, but basically how it works.

Slap on a new filter just to see if the filter is the problem, just in case.

Cut the old one open see if there's metal in it.

Drain the oil pan and see if there's metal in the oil.

Take off the pressure switch and put in a mechanical gauge.

Report back.
Thanks, that helps..

Lost pressure about 3000klm after build.. no mechanical gauge, just a warning light.. I bought a mechanical gauge today.. I will fit that, change the filter and see how I go..

The shaft from the distributor to the pump can be driven with a drill?

Thanks for your time and help.

Dunc.
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Old 12-23-2008, 08:49 PM
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My friends Vega with a 383 had the exact problem right after the motor was installed... The pump pickup fell off.
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Old 12-23-2008, 09:23 PM
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Quote:
Originally Posted by Zimmo
My friends Vega with a 383 had the exact problem right after the motor was installed... The pump pickup fell off.

my friend liked silicone so much , it would suck to the screen and light come on , gage drop to bottom .
push it back to pits and run fine ,good pressure .
back to track , same thing .drop .
only sucked it in when at 6000 rpms at the lights .
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Old 12-23-2008, 10:56 PM
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lost oil pressure

do you have any knocking noise's it could be the pick up tube fell off
oil pump pressure regulator stuck open in the small block first the oil is pulled through the filter then pumped throught the mains and rod throws in the crank also splits off from the rear main cap and oils both sides of the lifter bores from the lifters goes up the push rods through the lube holes in the rockers and splash lubes the valves and guides also the best way to prime is to use and old dist cut the advance off the top take the gear off and you should be able to pump oil all the way through the engine 's oil system
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Old 12-23-2008, 11:48 PM
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duncan_m,

Yes you can reach down and turn the oil pump but you will not build any pressure because the distributor housing needs to be in the block, otherwise the oil just gets pumped back into the lifter galley. So you need an old distributor with the gear removed and then a shim installed where the gear was.
A drop in oil pressure can be caused by a few things and since you did not say that the engine knocks I figure it has not spun a bearing which is good.
But if the pressure stays low don't keep running the engine until it does start knocking, then it is too late.
But two things come to mind as to what might have caused this. The first is rather easy. If the pan has been pushed up then the space between the oil pick-up and the bottom of the pan is now so small that oil can not get "sucked" up into the pump and the oil pressure drops.
The other thing that could have happened is that one of the three oil galley plugs at the front of the engine right behind the cam gear has been pushed out causing the pressure loss.

Good Luck
Scholman
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Old 12-24-2008, 03:58 AM
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heres my 2 cents.... if you have a MSD dist. with the adjustable ring loosen the ring,then u have to let the dist slide all the way in then pick up 20 thousands i had lost oil press. or had little flow & oil no reading on mech gauge. soon as i adjusted the dist OH WOW OIL flowing everywhere

Last edited by smrat; 12-24-2008 at 04:03 AM.
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Old 12-24-2008, 07:50 AM
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If it's just a warning light they are set to go on pretty low 20lbs or so.

Good advice up top, all things to look for. I went to metal in the oil because if that is the problem you don't want to be running that motor anymore.

the rest of it is benign.
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Old 12-24-2008, 09:47 AM
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Oil flows to the mains first, then the cam oil gallery. Mains always get lubricated first in any engine.

I would suspect the sensor is bad, pretty common, checking oil pressure manually is a good idea...you can just plumb an off the shelf gauge into the block to check pressure temporarily.
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Old 12-24-2008, 07:05 PM
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Quote:
Originally Posted by 4 Jaw Chuck
I would suspect the sensor is bad
Bingo!

I plumbed a mechanical gauge in and I'm getting 55psi at idle... and the sensor started working again at the same time.. I guess I knocked it enough to dislodge the fault in it..

I'll put in a permanent mechanical gauge and replace the sensor.

Many thanks to everyone! I can sleep easy tonight.

Cheers,

Dunc.
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