426 Hemi variable oil pressure

[elocho]

Good afternoon,

we have a A990 tribute with a stroked 426 Hemi where the oil preassure is behaving very suspicious. At idle it does hardly 8-10psi, at 2500rm it starts at 40psi but drops to 20psi after 1min of running approximately. The external oil pump has been replaced & checked, removing the oil pan indicates that the rorating assembly is brand new with just a few miles on it. I also tried 2 different gauges, both show the same fluctuation. Next stop would be to pull the engine and take it apart...but before going down that rout i thought i ask if that rings a bell for anyone who has had a similar issue in the past? Thanks for help in advance

 

[dvw]

Does it have a solid roller cam? Are the lifter bores bushed? Are you pushrod oiling, or factory to the rockers? What type of oil pick-up, Internal or external?
Doug

 

[elocho]

Hi Doug,
thanks for getting back, i did not built the engine / nor have i taken it apart (yet) but from what I can judge:
- solid cam
- lifter bore bushed - i do not know
- factory rocker oiling
- factory oil pickup internal

thanks

 

[snakeoil24]

Did you check rocker shafts are installed with groove facing down? Besides this really need an inspection of internals not knowing the history of this engine makes it difficult to determine what is going on.

 

[gtx6970]

Sounds like excessive bearing clearances

 

[69Bee]

Rod/Main/Cam bearing clearances excessive

 

[dvw]

We've taken apart engines with -.010" crank and standard bearings that had more oil pressure. The fact that it drops drops at RPM increase is telling us something. I'm thinking the pump supply is lacking. Look for a cracked pick-up tube near the threads sucking air.
Doug

 

[beanhead]

at 2500rm it starts at 40psi but drops to 20psi after 1min of running approximately.

Possibly excessive aeration? Does it have a windage tray?

 

[Runcharger]

It does sound like it's pumping oil up to the heads and then sucking air. One minute run time isn't enough to heat and thin the oil.

 

[PRHeads]

If you’re at the point where you’re thinking of pulling the engine, I’d pull the intake and run a priming tool and see if you can spot any excessive leaks.

Cam bearings, lifters, excessive oil running down from the heads, etc.

 

[Rich H.]

If you’re at the point where you’re thinking of pulling the engine, I’d pull the intake and run a priming tool and see if you can spot any excessive leaks.

Cam bearings, lifters, excessive oil running down from the heads, etc.

Good advice and worth the effort.

If no huge leaks are found on the top and the engine does come out, as an additional test before tearing it down it's also possible to view the entire lower end while pressurized and look for excessive leaks there as well (clamp a hose on a short section of npt pipe threaded into the block, run the hose into a bucket of oil, set a metal catch tray under the engine, run the priming tool and watch oil escape each rod pair). If there were something like a cracked internal oil pickup boss it might reveal itself with odd noises. It does make a mess, but not horribly bad if you do it quickly.

It's an old test from the days of poured-in-place lead babbit bearings and is not commonly done anymore, probably because of the mess, but can help give some clues.

 

[RemCharger]

A buddy's aluminum indy block rattled out the #4 cam bearing once. Pretty low pressure

 

[dvw]

The problem here is it loses pressure with engine speed. It also has idle oil pressure. Seeing these two parameters, it should gain pressure with engine speed. If there was an internal pressure leak I could see it not gaining enough pressure, but not losing pressure. This points to a delivery problem to the pump in my eyes.
Doug

 

[Dragon Slayer]

Do you have oil into the water or vice versa. What is capacity of the pan and do you have proper oil level?

 

[elocho]

thank you all for providing suggestions! a couple of responses:
i have a stock oil pan with 6.25qt and a stock oil pump - no high volume pump (reducing the pobability of not enough oil in the pan). There is no water in the oil, we had pulled the pan but it all looked like expected. Running a priming tool sounds like an iday to try although its on cold oil.
Thanks again for your ideas

 

[dvw]

When the pan was removed what was checked? Were caps removed? Clearance's verified? Pick up removed and inspected?
Doug

 

[73HEMI_RR_GTX]

Did you check ROD side clearance? Shouldn't run more than .017 max for a street motor. Also verify oil pick-up to bottom of pan clearance.
Back in 1980 when I bought my 1968 426 Hemi used. It also was a fresh rebuild with great oil pressure running a priming tool. Once I installed it in the Road Runner I noticed a similar oil pressure issue. It would start at 80 psi cold @ idle. Then after warming up it would dip to 8 psi @ idle, but would rise with rpm to 60 psi @ 4,000. I pulled the engine out and removed the pan to check crank bearing clearances and inspect the crank. What I found after measuring the lower end was the crank had been machined for .022 rod side clearance. It had Velasco stamped on the crank and the journals were hard chromed and polished for .0025 rod and .003 main clearances. So it appears that a used Velasco Chrome crank from a fuel race motor was used for a street build. I replaced the crank with stock side rod clearances solved the oil pressure issue. Now 80 psi cold 45 psi hot @ idle and 80 psi hot @ 4500 rpm. Just a note, I run 40w Valvoline oil since my car never sees below 40 degrees outside temps.

 

[elocho]

thanks again for the hints! i will check again carefully and let you know what i find.

 

[dvw]

Side clearance won't affect anything. The limiter is rod bearing clearance. Many engines built with Chevy width rod on a Mopar journal adding aprox .050" to the normal side clearance. The stock pickup should set on the bottom of the pan. Unless the shield is flattened against the screen it can't be to close to the bottom.
Doug

 

[Geoff 2]

I suspect the front oil gallery pipe plug has been left out.