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Fresh rebuild on a 360 we primed it had 50psi of oil pressure. Fired it up 70psi breaking it in a 2000 rpm oil pressure slowly dropping 10 minutes in down to 25psi after 20 minutes down to bout 10psi at 2000rpm back it down to 800rpm and it’s got bout 2psi shut it down. Drained the oil checked the filter nothing that goes that’s why. Any help would be greatly appreciated.
 

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Oil passages cleaned? Block cleaned prior to assembly? New oil pickup?

My bet is a blocked oil passage that kept getting more and more dirtier restricting flow......

Is it leaking anywhere? Smoking?

Neil
 

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Just a thought, how about oil thickness? your bearing clearances may be way to loose with the type of oil you are running. Is motor getting up to temp really quickly and losing oil pressure as a result?

Neil
 

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did you use DIESEL oil with the ZINK in it , if not you probly cooked the motor

diesel oil is the ONLY oil to use on FLAT tappet cam motors
 
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Try a thicker oil and see if it lasts longer oil pressure wise. It may be too loose in there and not building pressure. Did you buy bearings that matched your crankshaft being turned down?

Neil
 

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'79 Macho 360 Magnum, Comp 480 cam, Hughes springs, 650 Thunder AVS, Pertronix Flamethrower ignition
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Well, your cam bearing clearances, rod side clearances, main bearing clearances all play a role in oil pressure. I see you have roller rockers, what pushrods are you using? Are they hollow? Did you check the spring in the oil pump? Did you try a different gauge? Does the engine knock or tick loudly? These are the things I'd be looking at.
 
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'79 Macho 360 Magnum, Comp 480 cam, Hughes springs, 650 Thunder AVS, Pertronix Flamethrower ignition
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Does the oil smell burnt? I'd pull a cap or two to see what's going on for piece of mind.
 

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pull the oil filter, cut it open, remove the media and lay it out for inspection. It'll at least help you figure out what direction to go if you see any evidence of bearing material in the filter media.
 

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so it has good pressure when cold, but no pressure when warm. Initially it sounds like mismatched bearing clearances and it's bleeding to death past the bearings...but if the bearings were too big then you'd probably have some real noise going on. Even if you wiped out the cam you'd still have decent oil pressure. Oil viscosity wouldn't cause a no-pressure situation. The obvious thoughts are a purpose-blocked passageway is 'unblocking' itself when warmed up and it isn't retaining pressure, and that leads me to think along the lines of bad oil pump/bypass valve...
 
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Fix from an Old thread here, "NOW I'm getting pissed!" (pasted from it) but similar symptoms after a rebuild...sounds worth checking.

SpotShifter said:
Have you checked all oil galley plugs? There is a plug in the back end of the drivers side lifter galley that will allow oil to pour out, go straight back to the pan & give you low oil pressure. If you pull out the distributor & stick your finger down there you will feel a hole (if no plug), it's a 1/2" NPT plug I believe & it's trick to get it in with the motor in the truck (don't ask me how I know!). Ferlin
 
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