Oil pressure questions

Adam/Mill Valley CA

Adam/Mill Valley CA

Senior Member
My 1936 pickup has a 221cu in poured bearing motor which has always run well (especially now with rebuilt distributor by Charlie Schwendler and rebuilt coil by Skip Haney). Mileage/rebuild status unknown, I've put about 15000+ miles on it-it clearly was somewhat tired from the get-go,there is pitting in some of the cylinder bores, uses a bit of oil, but will easily go 65-70 mph (it has a 3.78 rear end)-I usually run 55mph on the highway.There is no oil filter, I change the oil (5 qts) every 1000 miles religiously, with Valvoline 20W-50 VR-1 racing oil.

I recently fitted a mechanical oil pressure gauge (and checked the #'s with a second high quality mechanical gauge); it registers 42lbs cold, 25lbs hot at 55 mph (the spec from the '36 Ford service bulletin is 30lbs at 55 mph). However, when hot after a freeway run, at idle, it drops to 0-2 lb
When I first got the truck I dropped the oil pan and cleaned out a ton of sludge, plastigguged the mains which were .002 (wear limit per Ford of .003)
The oil pump is a replacement type, the relief spring in the front of the valley was replaced with a new #50 spring.
I don't really want to rebuild this motor if I don't have to, but I also don't want to grenade the crank journals. Opinions from experienced motor guys?


Thanks,


Adam
 
Adam, your experience with oil pressure is typical for a flathead. I would monitor your lower readings for any future movement of sludge blockage of your pump, and increased oil consumption, but otherwise just enjoy your ride!
 
Re: Oil Pressure Quote:
Originally Posted by flathead4rd
Flatheads are more about volume than pressure. When mine is hot and idling on a hot summer day it's around 10 psi which is OK.

YEP! - This, from Ron Bishop's book "Rebuilding The Famous Ford Flathead" - Page 51 - "Ford used 40 non-detergent oil (Summer) in all of the flathead motors. The flathead oil system ran between 10-15 pounds of pressure, but is not considered a pressurized system by today's standards."- This for factory stock engines....
 
At hot idle it's still flowing oil, and it only has to pump it high enough to lube the cam bearings/valley oil tube since there are no oil passages any higher than that. It'll be just fine as is, but you might get a bit higher oil pressure if you installed a properly clearanced, good condition original Ford pump. That's only if you really want to...I'd not worry.
 
dont make it any bigger than it is [if it aint Knockin keep it rockin] use, enjoy but respect its limitations you may get a little more pressure from so called older engine oil 20w 60/70 not sure whats available in your area but should be ok if its from a quality suppler beware the snake oil there's plenty out there
 
I would appreciate some further input from knowledgeable engine guys about this motor. I did some further observations during our recent hot weather, and noted that after running awhile on the highway (about 55 mph or so) the oil pressure would be 18-20psi at speed, and zero at idle. It runs very well, as it always has. I tried straight 50 wt VR-1 Valvoline with no benefit; then put a new spring in the pressure relief valve at the front of the valley shimmed about 1/4", this increased the highway hot running pressure to a little over 20 but not the pressure at idle(as expected).
I decided to drop the pan and look at the pump, which I put in 15000 miles ago, it's an 8BA-type from Macs/Eckler which I suspect is offshore (metric bolts, no markings on the pump), helical gears, gear to end plate clearance .005, gear to wall clearance maybe .001-,002. The RT-type pickup looked fine, no sludge on the screen, or anywhere else for that matter
Checked the main bearing clearance with plastigage (which was .0025 15000 miles ago), now .0035-.004, no scoring. I think this is still within the wear limit of .005. Recall this is a poured bearing motor
So-I will replace the pump just because it is a PITA to take off the pan. I'm inclined to use a Mellings M-19 standard volume which I know John Mason (JM35) uses, but is there any rationale for going to a high volume pump (M-15)? I don't feature rebuilding the motor at this point especially given the difficulty re-babbittng a block these days, but I don't want to destroy it either. Because of where I live, it definitely needs to be able to cope with freeway driving to some extent.
Thanks for any input.


Adam
 
I want to reply but don't want to make any false statements.
If you have a freshly rebuilt tight engine the standard pump will be perfectly capable of supplying all the oil you need.
The reason your oil pressure is low is because there are a lot of opportunities for the oil to escape from worn (but not necessarily worn out) bearings. Remember the cam bearings also figure in the equation.
Pressure builds when the volume the pump is trying to supply exceeds the volume able to flow through the motor, due to natural leakage from all the bearings and other oil draw-offs like the cam gear chamber.
So, as you have plenty of leakage, maybe there would be a good reason to go for the high volume pump.
That's my rationale.
I have recently been investigating low oil pressure on one of my motors, so all this is in the front of my mind right now.
Mart.
 
If you opt for a high volume pump it’s probably gonna push more oil through the rear main than the slinger can handle therefore creating a big oil leak out the cotter pin hole under the clutch housing. Been there done it. I always like tight tolerance on the rear main to help prevent this.
 
Mart, I've certainly had thoughts along those line, but one issue that has been raised as Ken/Alabama noted is whether the high volume pump would push more oil out the rear main-which would be a particular concern with my motor since these early engines don't have a true rear main seal but rather a labyrinth type barrier.
I did have communication with alanwoodieman who put a high volume pump for someone in a motor which had low pressure, by his report it worked nicely to bring up the pressure and was still doing well a couple of years later.


Adam
 
Adam, I found it useful to see how much I had to raise the idle by to just lift the needle on the gauge off the stop. If that idle speed is not too high it is a reasonable compromise to make for peace of mind.

I had a motor with zero hot idle oil pressure and a change of cam bearings made enough difference so that it did show some pressure at idle.

Mart.
 
Hi Adam, I stand with Mart on this. If your already low on pressure and your mains are within spec's the excess volume should go out where the lose fits are and not the rear main.. In my 38 zephyr I ran a HV pump with the same rear main type seal with no problems. It idled at 15 and ran at 40 plus PSI. My oil pressure loss was do to worn lifter sockets.( the twelves had hydraulic lifters) Tim
 
Pete, thanks for the reference, interesting discussion. It certainly doesn't seem like ol' ron is too worried about oil pressure per se


Mart, even at low idle speed I assume there's still some oil flow as the bearings have not yet died. I do recognize this could be cam bearings-assume there's wear there too.I wouldn't consider a change short of a total overhaul, which I'm not ready to do at this point.


Tim, thank you for the real-world input, I'm still on the fence as to which pump to install


Adam
 
Re: Oil pressure questions-Update

I thought I would give an update on this issue. To recap, it is a 221 cu in stock 85 hp Babbitt bearing motor; with extended highway driving in hot weather oil pressure at 55 MPH (3.78 rear end, Valvoline VR-1 20/50) was down to about 18 psi, dropping to zero at idle. The motor continued to perform fine, as it always has, but I was concerned about the 0 psi at idle. It had a no-name/offshore 8BA #50 pump about 15000 miles ago, with an 8 RT pickup. The old pump actually spec'd out fine when I removed it.
After a lot of thought I decided to put in a new high volume Mellings M-15 pump(from Speedway, marked made in USA), which is reputed to increase the volume by 25%. The main bearings showed .0035-.004 thou clearance with Plastigauge (vs previous .002 thou 15000 miles ago-total miles on the motor unknown)-still within specs, I believe. As Mart has said, it is "worn, but not worn out"
With the new pump after a long highway run, including uphill at 55 mph on a warm day, the pressure at speed is 45 PSI( retained the original #50 pressure relief spring in the valley with a 1/4" shim), dropping to 18 psi at hot idle. I was concerned the increased volume might cause excessive leakage out the back of the crank since there is no proper seal there, just the labyrinth, but that has not been evident at all.
Time will tell if this will let the motor live a bit longer, and I understand I may be just treating my psyche here. I'll update again in the future.


Adam
 
Hey that sounds like a very positive result. It all makes perfect sense. really pleased you were able to reach a situation you are happy with.

Mart.

Edit: reading that old post with some well known contributors was interesting. Racing motors use loose bearings. Well, so do old "keep 'em rolling" flattys so the high volume pump is a no brainer.

Of course, a multi thousand dollar rebuild would be anyone's first choice, but you know, sometimes you just have to do what you have to do.
 
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Pete, thanks for that reference, interesting reading-I'm looking at these worn bearing clearances as similar to a race motor. Mart, I agree a rebuild is what I would like to do, but particularly with poured bearings, it's just not in the cards right now for me. It does seem like a good block with no obvious cracks or leaks, I understand it's possible to machine these blocks for shell bearings but I'm sure that would be a very expensive proposition. I'll just keep running it and watch for further changes-heck, it might outlive me (I'm 75) :)


Adam
 
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