I have a 1990 gmc k1500 , The original owners swapped the efi engine with a 1993 tbi 350. I just got done rebuilding this engine. I had the crankshaft ground, cylinders were bored .030 over and a new mid range cam shaft installed.
When the engine starts my oil pressure is fine. It hovers around 50-60 psi. At first i was told it could be a bad gauge or oil pump. i replaced the oil pump with a high flow pump and put a after marked gauge in as well. I am still having the same problem. when the engine heats up my oil pressure will drop down to about 4-7 psi per both gauges and i am out of ideas as to why. Any help would be greatly appreciated.

 

I'm assuming that the block was properly washed after the machinework was done, before assembly?
What were the bearing clearances on the mains and rods?

 

Cam bearings?

At the end of the day it doesn't matter - you have to tear it down. It's got bad clearances somewhere.

GD

 

Honestly i was hoping for some magic that it was a simple fix. i guess not. I have been having nothing but problems with the engine after i had it rebuilt. To keep the amount of wrench time i will need into the engine as low as possible. would it just be best at this point to put a new crankshaft and bearing kit in the engine when i pull it out again? and if so. is there any you would recommend i use?

 

I had the prep work all done before hand. This was the first time i rebuilt a engine and i was having a mechanic show me how to rebuild. i know the engine got hot tanked and honed. i do not know the clearances on the mains and rods. From what people are saying is this just a problem with to much clearance on the crank or cam?

 

The engine pumps oil to the cam bearings first on the SBC. Often loose cam bearings are responsible for low oil pressure.

When assembling the engine it is critical that all clearances be measured to ensure the correct parts are going in, and that the machine work was done accurately. Who purchased the bearings? I always have the machine shop order the bearings to match whatever they do to the block, crank, rods, etc. And of course I triple check their work and my assembly to ensure all clearances are as expected during actual assembly - if they are not then we stop and evaluate - possibly contact the machinist, etc. Personally - I get the best results from not touching the bores unless absolutely necessary - too often people go hog wild and want to do a bore job on perfectly runable cylinder walls - all this does is make break-in a much more unpleasant and sphincter exercising operation and needlessly removes material from the block making it weaker and less able to dissipate heat - the 5 whole cubes you get from a 30 overbore aren't in any way worth the trouble IMO. It's easier to just find a (Vortec) block with good bores. In addition I ALWAYS align-hone the block and square the decks with the pistons 0.025" in the hole (if possible) and have the crank matched to it and the rods matched to the crank.

GD