1991 GMC C1500 low oil pressure and over heating

REDDOGGG2124

MEMBER
1991 GMC C1500
V8
2WD
AUTOMATIC
129 MILES

I just had my 91 gmc 350 rebuilt bored out 30 over had rv cam installed used old heads and intake manifold put engine back in truck fired it up had 15 pounds oil pressure when it heats up pressure falls to 0 and it starts to knock. Now it is begining to overheat and knock when I first start it and continues to knock. Had ckank and bearings changed on the advice of mechanic. Still same problem. Guys ive been in this engine 6 times replaced crank 3 times to include main and rod bearings each time. Im stuck I need help if u guys have any ideas let me know. Thanks

2 Replies

JAMMER74

MEMBER
6 POSTS

Before the crankshaft and bearings were replace, what clearances were measured on the rod and main journals to bearings?Was the block flushed after the boring job?Was the oil pump replaced with a high volume pump?Is the oil pickup tight in the pump?Was the source of the knock determined after the initial job was done?Because the vehicle is overheating now, it really sound like you have a major oil supply problem, One last question, were the cam bearings replaced when the Rv cam was installed?

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Tuesday, October 27th, 2009 AT 8:24 AM

PEAR69

MECHANIC
1,482 POSTS

You have a serious oil system malfunction. My guess is -- when the block was bored out, it was not properly cleaned afterwards.
Any engine that is allowed to run -- to the point of knocking because of no oil pressure -- must be rebuilt. It does not matter if it is a factory new engine or a rebuilt engine, ---without oil pressure, there is irreverseable damage done to the crank, cam, and all the bearings. The block must be stripped and inspected to see if the crank and cam mains can be align bored and honed -- I suspect this was not done in the first place and I further suspect that this block is junk.
It will be cheaper to just put in a crate engine.

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Tuesday, October 27th, 2009 AT 8:35 AM