The Stovebolt Site Forums The Shop Area Engine Shop Excessive High Oil Pressure

Hello all,

I just finished rebuilding a stock '70s 292 I-6, and installing it in my 1955 Chevy truck. At start up, the oil pressure gauge pegged at 60 PSI, and I've got oil leaking badly out the rear main seal. I connected an oil pressure test gauge, and read 80 PSI at idle with it going over 100 PSI with some RPMs. The oil pump I used was supposed to be a "stock" replacement in a rebuild kit from Engine Tech. The cam timing set came with an aluminum gear, and there is a fair amount of whine coming from that, am assuming part of that is the load on the distributor drive gear driving the oil pump.

I did some surfing online, it seems that it's possible the oil pressure bypass valve on the pump is stuck and not relieving pressure. At any rate, I need to pull the engine back out and open it up.

Questions for y'all:

- Ever hear of a stuck oil bypass spring before?
- Can excessive oil pressure at the rear crank journal force oil past the rear main seal?

thanks,
JW

Yes and yes.

Yes, and "maybe" If there's enough oil squirting out of the rear main bearing it can overpower the tension of the lip seal against the crankshaft. Oil (or any liquid) can't be compressed- - - -if the clearance at the bearings can't leak enough back into the oil pan, the pressure goes up as a function of RPM. A fellow racer called me to see if I could adjust the carburetor on his new engine- - - -"it won't idle"! The engine would start, shudder a little, and stall- - - - -repeatedly. I finally told him to rev it up and keep the engine running long enough to warm it up so I could try to adjust the idle mixture. Start- - - -wide open throttle- - - -within 10 seconds it blew the side out of the oil filter and covered me in lukewarm oil. He had shimmed the relief spring down tight enough it wouldn't move, and pegged out a 100 PSI gauge at idle. I have no idea how high the pressure had to be to rupture a filter can! The stall was caused by a hydraulic lock at the oil pump stopping the engine from turning.
Jerry

I finally got the time to pull the engine back out of my truck and attempt to fix this issue. I hate trying to "fix" something if I don't fully understand the root cause, and lucky me, I found it.

I pulled the pan and removed the oil pump. Took it apart, removed the pressure relief spring, and tried to remove the plunger. It is stuck in there solid. The moron that assembled this oil pump had to have used a hammer and punch to get it into the bore, it absolutely will not come out or even budge a little. So, root cause: pressure relieve valve stuck closed, oil pump over-pressuring the entire system, and is likely pushing oil out the rear main bearing with such force it's blowing past the rear main seal. I have all the parts to fix it including a new oil pump. Will see how it goes in a couple weeks.

-JW

Was this a new oil pump or did you send it somewhere to be rebuilt?

All this new stuff is poorly machined, shoddily assembled, and OEM tolerances and specifications are ignored.

New, it came with an overhaul kit from Mabbco. It's been a while but I kind of recall the brand name Engine Tech. Hencho in Mexico.

-John

Order stock Melling brand pump.

Already have a new pump from Sealed Power, made in USA.

-JW