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Blog on oil pumps and such

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jlaird

jlaird

Great Pumpkin
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Now that I have had some days to think, consider the options, and check with folks in the know. I am even more sure that my oil pressure is a failing pump. Here's why.

Initial start up of engine when cold. 50 lbs @ 2K
Pressure decreases when engine warms to 185 degrees to 23 lbs @ 2k

Warm engine idle is 8 lbs warm and 20 lbs cold.

The harder I turn the engine, increase RPM, the better the oil pressure is.

I know for a fact that this pump is an old one. The only old, unrebuilt part in the engine.

Yes I will try the bearing trick in the overpressure switch thing first but hold no hope for that.

Remains to be seen of course wether a new pump is going to fix the problem but I feel real secure with my analysis.

Will also replace the clutch plate when engine is out and smooth out the 1/2 transmission detent to remove the sticking.

All in all it will be a good exercise. At least when I get it back it is road worthy, ie tages and insurance are in place.

Tomorrow I have a bit of surgery on my eyes for some nerve damage I had about 10 years ago. Doc says 100% fix is in the works. Should only take 20 min or so but will put me out of action for a few days, prob till next week in any case.

Raining here for a change and boy do we need it. Tis lovely.
 
Jack

Sounds like a plan, good luck tomorrow.

Pat
 
Jack, like I told you on the phone, when you get the pump out disassemble it, look for scaring on the points of the pump drive and check and make sure the scroll (the female section of the pump) is not cracked, make sure to take it out to check this, they look fine sitting in the pump body.
 
Yes sir I certinaly will. hehe.

Hap, I value your advise and guidance greatly. Rest assured that I will follow it letter by letter.
 
Jack, I hope all goes well with your eyes tomorrow. I had the exact same symptoms with my 948. 50 psi when cold, less than 10 psi at idle when hot. I too thought it was the oil pump because I too did not replace it when I rebuilt the engine. I was a college kid doing my first rebuild alone and did not get second opinions on things because I knew I could not afford to do it perfect. My mistake was in the crank and cam journals. They measured within the minimum, but barely. There were some lines in them as well, but I convinced myself they would be OK. I was not thinking about oil pressure as much as mechanical integrity. I know you were much more careful when you rebuilt yours, but I will ask the obvious- did you check the bearing clearances with plasti-gage? If it were mine, I would pull the oil sump while I had it out and check the mains again. Replacing the pump is a good idea, but I would recheck as much as I could while I had the engine out. Especially if you don't find obvious problems with the pump. I have never had that problem again since my first one. It's one of those life experiences that sticks with you. The 948 never gave any problem, but I was always worried about the oil pressure. After many years of being easy with it, I built a 1275 for the car. I'm going to rebuild it again someday and do it right. Best of luck to you.
 
Noop, did not use plastic gauge but the mains and journals are stock and were polished and measured by a machine shop.

Hap and I had a discussion on bearings. Seems there is a three part bearing material which is the best then some other one part kind. I will check that and make sure I have the good ones. Rest assured I will also double check bearing sizes with Plasti gauge when the engine is out.

Oh yea, if I need new bearings guess where I will get them. Haps the man for engine stuff. His word is my command.
 
Hap, I'm Right in your back yard in Piedmont. Been here 18 years. I was heavy into the hobby for about 5-6 years and then got too busy working an 8 to 5 and running a business. I'm catching the fever again. Still too busy to do as much as I want. I apologize to everyone here for not making an introductory first post. I just got carried away and jumped into the discussions.
 
"""""I know for a fact that this pump is an old one. The only old, unrebuilt part in the engine.""""""

Very rarely the old, not availiable new, "Concentric" brand oil pumps fail....unless they had trash put thru them.

Edit note.....the Concentric design was very good. The availaible pump now comes from a country of undetermined origin. It's style is different in that it has a flat cover plate which distorts.

Follow Haps recomendation re; the pump. Make sure the gasket is positioned properly and the three screws are not bottoming in the case (block).


"""""""Noop, did not use plastic gauge but the mains and journals are stock and were polished and measured by a machine shop."""""""

So if you dont find anything visually wrong with the pump, then bearing clearances are your problem. If the rod and main bearings are on the high side of clearance and the cam bearing(s) as well.....and the rod side clearance is excessive, and your getting an excessive amount of oil into the rocker shaft , the pump just cant keep up.The indicator here is that the oil pressure starts out ok when cold, then it decreases as the oil comes up to temp.....hot oil= thinner oil = less pressure.

Your easiest solution is live with the engine internals that you have and get (or make) an adjustable oil pressure bypass.


""""""""Seems there is a three part bearing material which is the best """"""""

Well yes, the old Vandervell Tri-Metal bearings are better than the now availiable aluminum backed pieces as they can take more loading than the ally's. But for a street motor the aluminum bearings are just fine.
 
JerryB Your easiest solution is live with the engine internals that you have and get (or make) an adjustable oil pressure bypass. [/quote said:
Yep I have one, and will try that next as soon as I eyes get to feeling better. Allthough it shows 62 pounds on startup.

If that does not do it and I can not find anything wrong with the pump when I pull the engine. ie no worn parts, I will send it to Hap for evaluation, if he finds no prob I think I just may plunk the engine in the back of my pickup and head up to Greenville and let the master look at my bearings and such and make durn sure all is well before it goes back in.

I owe Hap lunch in any case and would love a tour of his shop. Heck, might even learn how to use plastiguage.

Have a daughter in Alatana so would even take the wife that far or maybe she would go the whole way and we could checkout Biltmore house. Has been 20 years or so and understand lots more rooms etc are open.

Anyway, it is a pain but not a great big deal, just a pain.
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