Low idle oil pressure

[BOBBYR]

Hi Gang,
Hope you're all doing well. My 65 is running pretty good these days but after a good long ride the oil pressure is at about 10 psi.It has been recommended to me to replace the three inner main bearings and all the rod bearings.This project doesn't really bother me on account I was going to pull the motor ,this winter,anyway. My question is, has anyone done this and how did it work out? I was told this would bring the pressure back and lengthen the engine life around 50,000 miles.Any advice is appreciated
Bobby R

 

[Ed_K]

Hi Bobby,

Replacing the bearings will only help your idle oil pressure if they are worn out. How does the person that recommended this to
you know that they are worn out ?
Is your engine making any strange knocking noises ?
What is your oil pressure while driving say at 60 MPH ?
What kind and weight of motor oil are you using ?
Have you removed the oil bypass plunger and spring and checked the plunger head for a smooth , mating surface and the spring for proper length per the shop manual ?
A worn rocker shaft assembly is the more common mechanical source of low oil pressure than bearings.
My 65 had a little lower oil pressure than I liked until after I cleaned up the bypass plunger and stretched the spring back to the proper length. I also switched to Castrol Syntec 20w-50 after I learned that they put additives in the oil for our old solid lifters ( tappets ). That oil seemed to raise the oil pressure at least 5 lbs both at idle and while running down the road.

Ed

 

[GregW]

A worn rocker shaft assembly is the more common mechanical source of low oil pressure than bearings.

+1 on that. If it hasn't been checked, I'd do that first. If you do it yourself, it costs nothing, 'cept maybe a valve cover gasket.

 

[BOBBYR]

Hi Ed,
I have shimmed the spring which did boost the idle oil pressure by about 5 psi. Also ,the engine is not knocking. The oil pressure at 60 mph is at 65 psi. I know you are right that I should do some troubleshooting before jumping off this cliff. Tomorrow ,I will bring home another oil pressure gauge from work that I know reads correctly and start the process.In work, I rebuild alot of cummins deisels and the common problem with those engines are worn rod bearings.Oh well, like I said ,I guess I should start at the beginning. I don't know if a worn rocker shaft could cause this.I wish I knew more about that and knew a good test to check that.Get back to me if you can. Thanks for your help.
Bobby R

 

[Dave Richards]

65 PSI at driving! What's to worry about there, I'd say nothing. I get about 20 PSI at idle and 40-50 at highway speeds. I have 57,000 miles on the original engine, with no strange noises to date.

 

[MarkA]

Bobby,

The very next thing I would check would be the rockers shaft assembly. It sounds like they are worn and flowing too much oil which is hurting your low-rpm oil pressure. With the engine warmed up and at idle (and valve cover off), the rocker shaft and arms should only be dripping oil and not squirting or gushing. If you have very much oil flow on top of the head, it's time to have the rocker shaft rebuilt.

We have all gone (or will go through) what you are experiencing. My engine only had 64,000 miles on it when I had the rockers rebuilt. It made a big difference. I now get 30 psi at idle and warm. I used Rocker Arm Specialist: https://www.rockerarms.com

Mark

 

[BOBBYR]

Hi Mark,
Thanks for the e mail address.I talked with a friend of mine at Cummins Diesel and he has a pressurized oil reservoir that they use for leak down tests.With this tester, I can check all the oil clearances. I really hope it turns out to be the rocker shaft. Anyway , thanks again.
Bobby R

 

[Ed_K]

Like Dave said, 65 is a little high.
I now get 60 when the engine is cold and 53-55 at highway speed
after it is warmed up.
I get 20 at a fast idle but only 10 or so if it is idling very slowly like mine does after sitting at a stoplight for a while.
10 is a little on the low side at a fast idle. Probably the rocker shaft assembly worn/leaking a little.
What brand and weight motor oil are you using ?

Ed

 

[BOBBYR]

Hi Ed,
Going through the papers that came with the car,my dad always used 30w quaker state.When I got the car, I changed it and put in a straight weight again.I ordered parts from Moss yesterday ,and I'm Switching over to vr1 20-50w.That should help too. I'm sure it can't hurt. Anyway,it's running pretty good these days and I'd like to keep it that way.I'm going to check out this rocker shaft as soon as the gasket comes in and I'll let you know what I find. Thanks for your help.
Bobby R

 

[Stretch]

If you are going for an engine rebuild I recommend an oil pump from D Welsh. I think the commonly available new oil pump is weaker. When my engine was rebuilt the builder replaced my relatively new Welsh pump thinking it was old. Lost 5 psi in the deal.

 

[WALTER]

Correct me if I'm wrong but, doesn't the oil bypass plunger only prevent the oil pleasure from getting too high?

Walter

 

[Ed_K]

Hi Walter,

It works as the controlling mechanism for the oil pressure. That includes both limiting the pressure but it also " builds " the pressure.
If the oil pump is working right and you are not leaking too much oil around worn rocker arms;
.. If the plunger spring is weak ( shorter in length because the spring steel has lost it's shape), the oil pressure in the engine will be low.
.. If you add a spacer under the spring that is too thick, the oil pressure will be too high.
The spring and plunger both " limit " and " build " the oil pressure in the engine if everything else is working as it should.

... Did I get it right Dave ?

// Added the following edit to this post //

I just read Basil's post about Dave ! I had no idea !
I am real sorry to hear this news.
Dave, You are in my prayers !

Sincerely, Ed