Flathead High Oil Pressure

[Tod- NTCLC]

Rebuilt Flathead is now installed in the car - amazing - it started right up on the first quarter turn of the engine, and ran smooth as silk.  Followed all the advice about high rpm run-in for 30 45 minutes.

One thing that concerned me during the run in was that the oil-pressure gauge was pegged to high the entire time.  The gauge is good, and the un-rebuilt engine always indicated low-range oil pressure at idle, and went over to higher range at acceleration (as would be considered normal).  No leaks during the run-in, and for the few miles that I have been able to drive it, everything appears to be okay, but the oil pressure gauge has been pegged to high for almost all of this time - it came slightly down after heating the engine for a full hour, but touching the gas pegged it back over to full high pressure.  Dial gauge on the pressure port shows 65 psi at idle, going up to 90 at slight throttle.

This morning at idle (it is cool, not cold) the needle stayed over to full high pressure, and I suddenly got an oil leak at the distributer tower (where it bolts to the block).  This had not been leaking prior to today.  Not a seepage, but pumping out pretty good.  The tower was cleaned, mating surfaces wire brushed, relief hole in the bottom was clear and compressed air blown to get rid of any dirt out prior to installation, and the bolts are properly torqued. 

I know I can put a schmear of permatex on these surfaces and probably stop this leak, but I am worried that if the oil pressure remains this high, I am going to start blowing oil out the shaft seals and every other gasket.

No oil in the water.  No water in the oil.  I have not yet installed the bypass filter. 

One thing that is different on this engine (1948) than the original (1942) is that there was an oil fitting on the driver's side of the block towards the rear, pretty much in-line with the oil fitting that is midway on the block where the oil line ties in to deliver the oil to the top of the engine.  I can tell you that this fitting is under pressure because as I spun the oil pump prior to starting the engine, oil pumped out of this fitting.  I blocked this fitting off, and figured I would use it the bypass filter when the time comes.

So, any concerns or advice?  Have I missed something?  Anything easy that I can check out?

Here is a picture of the port that I plugged on the side of the engine if it means anything - pressure at this port is the same as the port for the gauge tube.

[Doug Houston]

The oil  pump has a regulator valve in it (AKA re;lief valve), that limits the oil pressure output to 30 PSI. It's simply simply a valve plug in the body of the oil pump, with a spring behind it. If the pressure starts beyond the designed pressure, the valve moves against the spring, to a point, where the valve plug opens a relief port, and discharges oil back into the crankcase. As the engine runs, oil is constantly being re-drained from the relief valve. If this doesn't happen, the pressure goes unchecked, and some rather nasty damage can happen to the oil pump drive, including that important bronze idler gear.

This sounds like the regulatolr valve plug is jammed,or has something holding it from moving, or possibly, the outlet relief port could be plugged, somehow. The pipe plug shown is possibly on all engines. I can't easily look at any of mine just now, but it is in the oil gallery, way past the outlet of the pump.

The oil leak at the distributor base is simply the weakest seal point at the present time, for the overpressure oil to be coming out. Were this my engine, I'd shut it down, and look at that oil pump, to find out what goes. I'd never run it again until this thing is solved. The problem has to be the regulator valve in the oil pump, somehow.

If this is a pump from another engine, now in the one you have, I would wonder if some hotshot could have put a piece of shaft stock in place opf the regulator spring to block the regulating action, and give the pump unlimited output. That would not be out of the question!

[Tod- NTCLC]

Thanks Doug - not exactly what I wanted to hear, but it could be worse.  Fortunately, I followed Walt Brewer's advice to only put gasket sealant on the oil pan and not the block - now I know why he suggested it!.

I am dropping the pan now, and will let you know what I find.  I don't see a very good description of the regulator in the service manual, but hopefully from your description I can figure out what I am looking for.

[Tod- NTCLC]

Guess what - you cannot drop the pan while the engine is in the car without doing some front end work, but I suppose you already knew that. 

So, here is what I have, but I am not exactly sure of what I am looking for.  From appearances, everything looks fine, and I don't see any real problem, but then I don't know what to expect.  I see an opening that might be what you are referring to as the relief port on the top side of the pump (see pic).  It appears to be clear as far as I can tell - no clearance to really get anything down into it.

Then, on the other side of the pump where the pick-up float is located, just above I see an opening.  There is a cotter key stuck across this, and it does not appear to have been properly set (poor workmanship?).  Is this where I should be looking for the spring?  Or do I need to drop the four bolts off of the bottom of the pump in order to sort this out?

Thanks for taking the time to look and advise - I really appreciate it.

Tod

[Mark Lowery]

Tod,
Remarkable how similar oil pumps are from manufacturer to manufacturer!  Other than the pickup assembly, this could be out of an Alfa Romeo, the engines I'm most familiar with.  Anyhow, yes, you need to remove the cotter pin.  Since there is a coil spring behind it, you may have to push in on the spring retainer that is bearing against the cotter pin while you remove it.  I agree w/ Doug in that the problem must lie in the by-pass valve assembly.  My bet is that the piston that the spring pushes against is seized in its bore in the position it ends up in when the engine is stopped.  Was the pump supposedly re-built?  This is a condition that can be bench tested but seldom is.  Also, a spec is probably available for the free length of the spring, but obviously, over time, the spring would tend to get weaker which would lead to the opposite condition your are experiencing.  One other explanation is that in the process of "rebuilding" the oil pump, someone substituted a spring the is too long, to stiff or both.  BTW, once the spring is removed, the piston should come out by inserting a magnet assuming it is not seized in the bore.

Mark Lowery, CLC #25216

[Bob Schuman]

Tod,
Cadillac specifications for the oil pump spring specify free length of 2-25/64 inches, and a force of 5-1/2 to 6-1/4 pounds to compress it to 1-13/32 inches. The regulator plunger should have .002 to .0035 inch clearance in the pump body. As others have stated, after taking out the cotter pin, the spring retainer, spring, and plunger should be free to come out.

Oil pressure should be 30 psi at operating speed and at least 15 psi at idle with warm oil, per the manual.

The small plug in the oil gallery at the left rear of the engine is where the oil pressure gauge was connected on earlier models. My 1940 has the connection there, my 48 engine has it next to the distributor tower.

Incidentally, to remove the oil pan after removing the sheet metal air deflector under the front part of the pan, if the pan won't come out, rotate the engine enough for the crankshaft counterweights to give more clearance(trial and error) and the pan will come right out. I learned this after dropping the steering drag link to get enough clearance.

Be sure to let us know the outcome.
Bob Schuman,CLC#254

[Tod- NTCLC]

Thanks for the information -

I will pull that cotter key tomorrow and see what we have.  My fear is, based on all of the input, the rod is going to be seized in the bore of the pump - not sure what the answer will be to get it out if that is the case.

Bob - where did you find that information?  My service manual does not go into any where near that amount of detail on the pump, and I was trying to figure out how I would test the spring or figure out if I had the correct plunger if I do get it out - very helpful.  Does what you have happen to mention how long the plunger should be?  And thanks for the tip on pan removal - I was looking at the front end assembly to see what was going to be involved in dropping that center link to get the pan off.  Happy to hear that I won't have to start on my front-end rebuild just yet!

I will let you know what I find tomorrow.

[Mark Lowery]

Tod,
Just a partial answer here;  the device for testing the spring length under load should be available at a good automotive machine shop.  Its primary use is testing valve springs.  The same principle applies here, but again, unless someone substituted the incorrect spring, an old spring that has been service for  some time would tend to experience more deflection under the specified load, which would lead to the pump bypassing at a lower pressure, obviously not your situation.

Mark Lowery, CLC #25216

[Carfreak]

Bob - where did you find that information?  My service manual does not go into any where near that amount of detail on the pump

Modified Chapter Docs:  
http://www.modifiedcadillac.org/documents/1940s/1944/1944%20Light%20Tanks%20Service/tn/1944%20Light%20Tanks%20Svc-66.jpg.html

[TMoore - NTCLC]

...ah, the tank service manual.  I have spent hours reading that, and forgot to go back to look for information about the oil pump - thanks for the reminder.

First, thanks Bob - a few bumps of the starter, and the pan slipped right out, which made the rest of my day much simpler.

I pulled the cotter pin out, and the spring came right out - measurement appears to be right on for the size.  I picked up a magnet that would fit into the bore - no joy.  After looking at things, I decided it would be okay to pull the pump off of the block so I could work on the bench.  Looks like I need to order a new gasket for that, but I wasn't going to make any progress under the car.

With the pump out, I shook, tapped, blew, poked, flushed, and still could not get that valve out. I finally opened the bottom of the pump and with the air compressor and lots of patience, the valve came out.  Seems to me it was really jammed in there.  I could not find any scoring or other marks, but I cleaned it with some steel wool and it now appears to slide in and out of the bore with no resistance.

One piece that was not in the assembly was the regulator spring retainer that is listed in the tank manual.  It just wasn't in the assembly when I pulled it out - the spring was held in place with the cotter pin.  I wouldn't think this would cause the high oil pressure (opposite should be true).

I am going to try to order the gaskets tomorrow, and see if I can locate the spring retainer, and hopefully get everything back together.

My guess at this stage is that the valve was simply hung up in the bore, and was not able to open to regulate the pressure.  As soon as I get all the parts, I will try a test run before I buckle up the oil pan to see if I made any progress.

Thanks for all the advice, and I will follow-up with the final results.

[J. Friedman]

I have a '49 OHV motor, but had the same problem once when I bought and installed an oil pump rebuilding kit as part of an engine rebuild.  Upon starting the engine the oil pressure was unnecessarily high.  Pulled the pan (easierr on a '49, as it comes right off when the idler arm is unbolted, allowing the center link to be lowered) and took apart the rebuilt oil pump on the bench.  Found the spring supplied with the rebuild kit to be much stiffer than the original, which I still had.  Apparently, the supplier of the kit threw in a spring which looked like the original spring, but without any regard to the difference in spring pressure.  As my original spring looked to be in perfect shape, I re-installed it and the oil pressure has been normal ever since. 

[TMoore - NTCLC]

Long overdue follow-up on this issue.  After calling several of the vendors, and getting mostly "no" when I asked to purchase just the spring for the oil-pump, I finally got a vendor to sell just the spring after reading that another member had had success.

Received the spring (along with another gasket set), removed the existing spring, and installed the new spring.  Started car and...64 psi oil pressure.  No improvement.

So, taking J. Friedman's suggestion, I opened the pan on the old engine, pulled out the original spring, and put it in the new engine - oil pressure is now exactly where it should be.

Thanks for all of the tips - I can now feel a little better about driving the car without the chance of blowing any seals or stressing out the bronze idler gear.

[Jay Friedman]

Tod,

I'm sure you are very pleased that you finally solved a worrisome problem.  For my part, I'm pleased my suggestion helped.

Jay Friedman

[markl]

Tod,
Just in case one of your fellow CLC members is tempted to put a new spring into their flathead oil pump (yeah, in particular, me), would you mind telling us where you got the spring that is apparently out of spec?  If that vendor is reading the message forum, they might want to review this issue w/ their supplier.  With the information Bob posted, it should be a simple matter for them to test their stock of springs.  I doubt if it was just one bad apple, more likely they have a barrel full!

Mark Lowery, CLC#25216

[Jay Friedman]

I think the moral of this story is that if you have an old car "Never, ever, throw anything away." 

[Otto Skorzeny]

And if it ain't broke, don't fix it.