Oil pressure drop as RPM increase

75 Jeep CJ5 401

OK Here is my problem, I have a fresh rebuilt 401 with cross drilled crankshaft, a bigger than stock cam, I installed the internal oil bypass line in the right lifter oil galley and put a restrictor in the left lifter bank, enlarged and added the drain holes in the lifter valley and timing chain cover bottom. My oil pressure is 25-27 PSI at idle, 17-20PSI at 2000RPM, and 15PSI at 3000RPM. I don't want to push it past 3000RPM until I figure this out The pick-up to pan clearance is 3/8" and I'm sure that the pan is not sucking up to the pick-up tube, which is good with no cracks. I double checked the clearance of the pump housing and gears, and everything is good there. I've tried the NAPA gold filter and the K&N filter with same results. I'm still getting the same problems with the pressure drop at RPM. Pulled the intake, removed and plugged the bypass line, and hooked up the drill. At full speed with a Dewalt 18volt I got steady 40psi, I didn't see anything obvious, some bleed by at the lifters and the pushrods kind of just pored out no gushing of oil, and not apparent hemorrhaging of the cam bearings. I let it sit for approx 45 minute and restarted the drill two pushrods on the passenger side shot oil out then air popped out as if there was and air pocket some where in the back side of the lifter oil galley. Have I forgotten to check something simple before I start yanking it out of the Jeep? Bill

jeepsr4ever

75 Jeep CJ5 401 wrote
OK
Here is my problem, I have a fresh rebuilt 401 with cross drilled crankshaft, a bigger than stock cam, I installed the internal oil bypass line in the right lifter oil galley and put a restrictor in the left lifter bank, enlarged and added the drain holes in the lifter valley and timing chain cover bottom.
My oil pressure is 25-27 PSI at idle, 17-20PSI at 2000RPM, and 15PSI at 3000RPM. I don't want to push it past 3000RPM until I figure this out

The pick-up to pan clearance is 3/8" and I'm sure that the pan is not sucking up to the pick-up tube, which is good with no cracks. I double checked the clearance of the pump housing and gears, and everything is good there.

I've tried the NAPA gold filter and the K&N filter with same results. I'm still getting the same problems with the pressure drop at RPM.

Pulled the intake, removed and plugged the bypass line, and hooked up the drill. At full speed with a Dewalt 18volt I got steady 40psi, I didn't see anything obvious, some bleed by at the lifters and the pushrods kind of just pored out no gushing of oil, and not apparent hemorrhaging of the cam bearings.

I let it sit for approx 45 minute and restarted the drill two pushrods on the passenger side shot oil out then air popped out as if there was and air pocket some where in the back side of the lifter oil galley.

Have I forgotten to check something simple before I start yanking it out of the Jeep?

Bill

Bill your lucky if your not restricting the mains behind the valley hole when you plugged this hole. Their isnt much meat there for a plug and the valley line if done wrong can be restrictive as well. Just a heads up on this one. You probly achieved 40psi with the drill because of the main blockage. What was the condition of your oil pump? What year is your oil filter adaptor? Sometimes a stuck pressure bypass plunger or oil bypass plunger can cause this as well as a worn out timing cover. Also did you or did your machinist check the crank specs with plastiguage?

75 Jeep CJ5 401

The cover is new so I assume that the filter adapter is the new style, the one that is angled right from the mating surface, and has the filter bypass closed off. If the plunger was sticking or stuck I don't think I would get 40PSI with the drill, but I could be wrong. I'm going to install a temporary rod into the back side of the plunger to hold it into place and test it again tomorrow I did the plastic gauge myself and I got no more than .002 most where .015 on all gearings, mains and rods. The only thing that I didn't do was measure the new cam bearings to the new cam, but I drilled new slightly smaller oiling holes in all of them except the front one. Thanks Bill

75 Jeep CJ5 401

:!:
OK
Well, I finally got lucky and figured it out!!!!
I install a rod behind the cap for the plunger spring to hold to plunger closed, started it up and the oil psi jumped past 80 (80 max Steward Warner gauge) at idle and blow the gasket out, what a mess.
I had another oil pump kit, a Clevite #601-1260 so I put that in in-place of the new Melling kit I was using.
WaaaLaaa!!!!! Oil pressure at idle steady 45psi, and 70psi at 3000rpm. I measured out the plunger and the spring on both kits before installing the Clevite kit and they where the same, the spring must have been the difference, I couldn‚Äôt tell from squeezing them if one was stronger than the other.
The added volume at higher rpm must have been opening the plunger and dropping the psi.

I want to thank everyone for the advice and info, hope this helps someone else down the road.

I know it was driving me madd, just ask the wife!!!!

Go figure, I fixed it on mothers day.

:t:

Goose

Glad it was an easy fix..! And If you are anything like me when an engine problems has you stumped.. your wife just got the best present for mothers day possible.