Rebuilt lt1 no oil pressure - Chevy Impala SS Forum
 
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post #1 of 7 (permalink) Old 05-20-2019, 03:31 PM Thread Starter
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Rebuilt lt1 no oil pressure

Just rebuilt my LT1, machine shop did crank and bearings, i did cam and all the top end stuff. I've started it up and i've got about 20 psi oil pressure that goes down to 8 when it starts to warm up. Put 20w50 in it and it get a few psi better, but low oil pressure light is coming on and my mechanical guage is reading 10. When i blip the throttle i get instant oil pressure to 40+. Is there something i'm missing here???

Used a melling select high volume pump
replaced the nylon sleeve with a metal oil pump rod

I font have my bearing clearances with me at the moment but they were extremity close the same clearances i had 9 years ago when i did the bottom end myself.

Last edited by fast lt1; 05-20-2019 at 03:48 PM.
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post #2 of 7 (permalink) Old 05-20-2019, 05:34 PM
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"general" rule of thumb is a SBC needs 10 psi per 1k rpm

10 at idle and 40 with rev would seem "ok" although with a HV pump you would typically see more.

would be interesting to know what your bearing clearances are...and that they were measured. Often crank is ground to .010 under requiring a +.010 bearing

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post #3 of 7 (permalink) Old 05-20-2019, 07:11 PM
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You're getting 8 psi with 20/50 oil? On a rebuilt mill? No bueno - not by a country mile. Did you do the work yourself? What was done to the bottom end?

10 psi/1000 rpm is spec for an 'average' lt1. One fresh out of the machine shop should easily double that @ idle. You have an internal leak somewhere - that much is certain.


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post #4 of 7 (permalink) Old 05-21-2019, 06:46 AM
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The front oil galley plugs are pressed in and replacements
are known to be loose and should always be tapped with threads
for screw-in oil galley plugs.
Pull timing cover and timing chain and check behind the cam sprocket that the
plugs haven't pushed out..

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post #5 of 7 (permalink) Old 05-21-2019, 08:06 AM
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It certainly is possible that the crank is undersized on the mains or rods by a few thousandths, but definitely not .010" You would know that as soon as the engine ran, as it would be knocking without question.

Did you happen to save the old bearings?
Did you measure the crank prior to installation?
Did you check clearances with plastigauge?

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post #6 of 7 (permalink) Old 05-21-2019, 03:37 PM
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would not putting in the check ball back in the oil galley that goes in/out (interference fit)from the rear main cap area (can't remember wich side) cause low oil pressure??

Given motor was rebuilt, IDK if this step was skipped....

\'96 BBB 383/T-56
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post #7 of 7 (permalink) Old 05-27-2019, 01:47 PM
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this happened to me one time and was a problem with grinding the crank journals .01 under and putting in std bearings and the pressure would increase with high revs but fell to very low levels at idle. for your sake i hope it is an oil galley plug.
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