Only 40lbs oil pressure after re-build.

[Xray50]

Ok. Question for you engine guru's! Just re-built big block chevy. Main bearings plastigauged within specs. 40 lbs of oil pressure at idle. Wen I rev up t stays at 40psi. The plugs are in the lifter valley and behind the cam shaft. What else can I look at and check?

[WETTE VETTE]

Hook up a mechanical guage and see if it agrees. Have you changed the oil and filter since break in?

[Ratickle]

That's weird.......


First the double check as said.....

[old377guy]

That's weird.......


First the double check as said.....

So there you have it xray, Paul in our technical dept. has determined that it is weird

[Ratickle]

So there you have it xray, Paul in our technical dept. has determined that it is weird

What do you expect???????


I'm from Oregon......

[old377guy]

I know, I know, "Keep Portland Weird" etc. etc. etc......... you'd think that all the weird had washed out of your system by now Paul,... Now back to our regularly scheduled thread about oil pressure...

[ROGUE]

First thing that comes to mind is the pressure relief valve in the oil pump. Was the spring removed before the pickup was welded on? If not, it could have gotten hot and lost it's "spring" . If are sure of all the oil plumbing and the preesure reading, I would change the oil pump first.

[Mopower]

Had an engine do a similar thing. Only 40 lbs cold and would drop to 5 lbs at idle when warm. Running 30 to 35 lbs. Problem turned out to be rods. Top to bottom they miked good, side to side at the parting line they were way large. Squashed then a bit in a press, clipped them and resized them until they were round. Then 70 cold, 60 warm and running and 40 at idle warm
Just my experience

[ROGUE]

Yeah, I cringed when I read you used plastiguage, thats not an accurate way to setup an engine. And like Mopower said, rods have to be resized. By your brief description, I took it to mean that you have 40 lbs all the time, idle and wot, hot or cold, if thats the case, look to the oil pump relief valve.

[Xray50]

Changed oil pump and working fine now. I'm guessing it was something with the relief valve. There must be a piece of metal or something stuck in it. I'll see if I can get it apart and find it just for confirmation.

[ROGUE]

Cool, glad you found it.

[Xray50]

Hey Rogue. How do all the pro's build engines? do they mic the inside of the crank and then mic out on the rods?

[ROGUE]

Hey Rogue. How do all the pro's build engines? do they mic the inside of the crank and then mic out on the rods?

I use a good set of micrometers, outside set and inside set. I prefer Starretts. They need to be accurate to a tenth and everything must be temperature equalized. I check three spots on each journal then the same at 90 degrees off and then mount each bearing and check them also. If anything is not right where I want it, it gets remachined. Sometimes I use bearings that are 1 under or 1 over if that gets me the right clearances.

[Blue Thunder]

Yes, what rogue said. You use 1/2 shells in 1 over/under to get the .0005".

[afr]

when i assemble a engine i always do both mic crank and rods torqued up and plastic gauge to see if they match kinda a double check thing
i have seen the cam bearing be off a bit and give a low pressure reading as well you got lucky a pump is far cheaper
another check i do on a new motor is after the break in oil i cut the oil filter open to read how the break in went

[Xray50]

Thanks for all the great info. I may have gotten lucky this time but will do it better next time. If you want to go fast you're going to pay for it one way or another. No engine lasts forever. I want triple digits. As soon as I get the engine broken in I got to get my slip factor down. I'm at 18%! Way to high for my Cat! I got to wait acouple of months. My wife will have me sleeping in the garage if I drop $1500 right now for a 5 blade!