The guys at the shop started my motor for the first time today. Initially they had 70 pounds of oil pressure. After running the motor for a couple of minutes the oil pressure at idle dropped down to around 10 pounds and when you rev it up they can hear a little rattle or knock. It sounded like it was running smooth before it warmed up. Any thoughts??

The engine is a 72 340 bored 40 over with basically a stock rebuild.

I spoke to the guy who assembled the engine in 2004 and he thought it could possibly be the pressure relief on the oil pump not working properly. Everything in the engine was replaced with a new rebuild kit after it came back from the machine shop.

I have zero knowledge when it comes to engines so I am acting as a go between trying to get information. I know that if there is help out there, I can start here for info.

Thanks for any input
Scott

Maybe they used a thin break-in oil, and the timing is a little too advanced causing some slight detonation.

Check the valve adjustment/ lifter preload, change the oil and filter(cut open the oil filter and see what it's caught) and double check the timing. Let us know what the initial timing is set at and the what the total timing is too.

How accurate is the gauge?

Did you use a 340/360 oil filter plate (8 holes) or a 318 (4 holes bad news)?

Was it overheating?

HV, HP or stock oil pump?

There is a plug inside that if it doesn't get installed will cause low oil pressure . Did they prime the engine with a drill before starting it ?

assuming the gauge is correct i would hesitate to run that engine any more until the problem is diagnosed and resolved. low oil pressure and knocking isn't what you want to hear from a new build. with regards to the pressure relief not working correctly he's thinking it's stuck open, this would to some extent affect the oil pressure under all conditions and it might not have made 70# if it's stuck open some.

Are you saying this engine was built in 2004 and never started. Lots can happen in 7 plus years. A Friend of mine just started one that sat half that long and the same thing happened with his oil pressure. He removed the oil pan and a mouse hade built a nest in his oil pan and plugged up the oil pickup. MORE INFO WILL BE NEEDED.

Thanks for the replies. I just got a call from the shop, they dropped the oil pan and found the clearances on the crank off by more then 20 thousands, so back to the machine shop she goes......

I spoke to the guy who assembled the motor and he said he plastigauged it back then and found everything to be within the correct tolerances. Does that make sense??

It's only money right?

My bad on this last posted info, what they told me is that the crank was ground 20 thoundsand and the are finding clearences now between 5 and 6 thousands.

So we contacted a new machine shop (because the one I used won't take an assembled engine) who is going to tear down the motor check everything out, fix it up and reassemble it the right way.

How much I ask................that remains to be seen.