Uphill oil leak

Bob Johnson

Bob Johnson

Well-known member
A rebuilt engine with less than 500 miles. Minimal leaks on flat ground running or not. But when parked on an uphill grade with the engine running there is a significant leak out the rear main. This is not a drip it is an actual stream of oil coming out the hole at the bottom of the flywheel housing. Drove it uphill about 100 ft, parked, shut off engine. There was just a few drops of oil. But started the engine while on the hill and after about 10-20 secs the flood started. Again this does not happen when the car is on flat ground. I am going to drop the pan and remove the rear main cap. I will look at the usual suspects. Has anyone had a similar uphill leak? If so what was the cause?

Bob
 
Not had the leak (just the opposite actually) but one can imagine ALL the possibilities.

Plugged drain tube.
Non-existent (broken/vibrated off) drain tube and crank windage.
Cracked thrust bearing (they are fragile)
Excessive end play (on the hill the crank/flywheel is wont to go 'back' leaving space between the thrust and collar.)
Gasket missing between engine and flywheel housing (leaks out the rearmost bearing of the camshaft and this is fed by oil buildup in the valve spring/tappet gallery)

I don't think this is merely "sealant" issues in the rear main/oilpan area (as are many leaks.)

Joe K
 
Keep the oil level halfway BETWEEN the "L" and "F" marks on the dipstick. The difference between that and at "F" is less than 1/2 quart, so you will not be starving the engine for oil. When the oil is at "F" on level ground, that's too high and when the car is parked on a steep incline with the nose of the car pointing uphill, the extra oil will be too much for the rear main "seal" (it's not a seal!) to hold back. So, the excess oil drips out. This is not a problem in Nebraska or Kansas, but it can play havoc in steep hills/mountain areas of our country. Try draining a little oil until you reach the halfway mark and then see if the leaking continues. There will still be residual oil back there from earlier steep incline parking, so don't expect the problem to go away immediately.
Marshall
 
If the engine was done in the original manner, there is NO rear seal. There is a slinger at the rear of the crankshaft to help hold back the oil in the bearing untill it can run down hill in the passage of the rear main bearing cap and out the drain tube, back into the oil pan. When the car goes uphill, the oil will flow backwards and can overpower the rear oil slinger and enter the flywheel housing. It doesn't matter whether the engine is running or not, the oil flows by gravity from the valve chamber to the mains untill the oil all flows out of the chamber, either into the oil pan or on the ground. When you get a large build up of oil in the flywheel housing, the leak will be a stream instead of a drip. Sounds like the engine has issues and needs to go back to the rebuilder.
 
measurements

I did some measurements as follows;

The grade that I test on was 9 degrees
The oil level at the FULL mark is 3.5" below the bottom of the block
The oil level at the LOW mark is 6" below the bottom of the block.

With the oil at the FULL level and at a 9 degree angle the oil level at the back of the block will be 1.86" below the block. The bottom of the rear main cap is 2.25" lower than the bottom of the block. The bottom of the oil return channel in the rear main cap is 1.75" below the bottom of the block. The bottom lip of the slinger channel at the back bottom of the rear main cap is 1.25" below the bottom of the block. So with the car on a 9 degree slope the oil will touch the bottom of the rear main cap. But it will be lower than the oil return channel in the cap. It will be lower than the back of the slinger channel.

With the oil at the LOW level and at a 9 degree angle the oil level at the back of the block will be 4.36" below the block.

The oil return channel (passage) in the rear main cap has an angle (drop) of 7.5 degrees.
Bob
 
Bob, with out having to type so much, check the end play in the rear main in thousandths, and the up and down movement in the rear main in thousandths.

On a grade like you have, you will get oil, but if those two things are off, you still may be able to improve things.
 
What Herm says but you will have to take things apart to check. When parked on a steep incline the front of the rear main cap and drain tube will be higher than the rear of the cap and slinger. Oil must flow past the slinger to enter the passage in the rear main cap and flow downward at an angle to the drain tube. When the drain tube is angled much higher than the slinger , oil will flow out at the least point of resistance, usually out the back of the rear main into the flywheel housing and then on the ground. It mostly has to do with gravity. The engine may be OK. My first choice would be to park on fairly level ground and see how it does.
 
Marshall V. Daut said:
This is not a problem in Nebraska or Kansas, but it can play havoc in steep hills/mountain areas of our country. Marshall
Click to expand...

Now Marshall we have our share of hills here in Nebraska. Folks just drive I-80 along the Platte River and think the whole state is as flat as a pancake. Go a few miles in either direction off of I-80 and it's a whole different ball game. No mountains but hills we do have.
 
Well, Dave, I just won't park my Model A full of oil on one of your Pike's Peaks. :)
Yes, I have driven through Nebraska many times from the 1950's through early 1980's when my cross-country route changed. I don't recall many steep hills - at least not steep enough to make Model A's leak - but these drives were mostly made at night. Should we visit Colorado again from eastern Iowa, I'll be sure to check out your statement - but in a modern car with a REAL rear main seal. :)
Marshall
 
Re: measurements

Bob Johnson said:
I did some measurements as follows;

The grade that I test on was 9 degrees
The oil level at the FULL mark is 3.5" below the bottom of the block
The oil level at the LOW mark is 6" below the bottom of the block.

With the oil at the FULL level and at a 9 degree angle the oil level at the back of the block will be 1.86" below the block. The bottom of the rear main cap is 2.25" lower than the bottom of the block. The bottom of the oil return channel in the rear main cap is 1.75" below the bottom of the block. The bottom lip of the slinger channel at the back bottom of the rear main cap is 1.25" below the bottom of the block. So with the car on a 9 degree slope the oil will touch the bottom of the rear main cap. But it will be lower than the oil return channel in the cap. It will be lower than the back of the slinger channel.

With the oil at the LOW level and at a 9 degree angle the oil level at the back of the block will be 4.36" below the block.

The oil return channel (passage) in the rear main cap has an angle (drop) of 7.5 degrees.
Bob
Click to expand...
Bob, they will all leak if the front end is too high, especially if the oil level is at full or more. Ford recognized this as a problem especially on AA trucks which were used for grain and lifted by grain elevators. He had oil tubes with a check ball in them to solve this problem. The best way to keep this from being a problem is to run the oil level half way between F and L.
 
Bob--Try some lesser grades before tearing it down. 9* is a pretty good grade and I would first think the slope is causing the oil that comes down the feed pipe to flow to the back, especially as the cap drain to the pan is 7.5* (I have never seen that figured before, thanks.) I drove a new rebuild to a friends house, up a fair grade, to show it off, and panicked when there was a stream of oil coming out when I got there. Drove it home prepared to pull it and redo stuff, but no oil leaking when I got home. No further problem. I just don't visit that guy any more. (-:)
Again, try the easy stuff first.
 
I typically run with the oil in the lower third of the space on the dipstick. All the dipstick measures is the depth of oil in the pan. The true lubrication is done by the dipper tray and oil pump (which cares not how much oil is in the pan as long as the pump suction is covered.)

Maybe that's why I've never had much oil come out through the rear main?

Joe K
 
Not tring to be disagreeable but ... I can't see how oil level , as long as it is reasonable will have any effect on the leak.Its the oil in the valve chamber that is leaking through the rear main, not the level of the oil in the oil pan.
 
Additional info

I did some calculations and with the oil level at the FULL mark and the car on a 9 degree grade the oil level at the back of the engine will be 1.86" below the bottom of the block. With the oil level at the LOW mark the oil level at the back of the engine will be 4.36" below the bottom of the block. The bottom rear main cap is 2.25" lower than the bottom of the block. The bottom lip of the slinger channel at the back of the rear main cap is 1.25" below the bottom of the block. Thus the oil in the pan would have to go uphill to drain out the back of the rear main.

I spent all day trying to stop the leak.

Initial condition of the rear main cap. The shims were installed with a gray sealant on both sides of the shims (0.032" shims). There was heavy sealant around the corner where the curved cork gasket meets the bottom of the block. The babbitt in the cap did not have an oil groove and there was not a relieve at the top where the shims are located.

I ran the engine while up on a lift and I looked into the inspection hole at the front bottom of the flywheel. I could not see any oil leaks. I rasied the front of the car to about a 4 degree angle, not leak. I raised it to about 6 degrees and there was a leak. Looking through the inspection hole I could see that the oil was coming out the back of the rear main. There were no visible leak along the full length of the shims on either side.

I cut the relieves in the babbitt at the top edges and cut a groove from the front to the back in the proper direction. By the owners request I also drilled a hole through the babbitt at the midpoint of the groove down into the oil return channel. I checked the clearance of the bearing after removing the gray sealant on the shims. I check several places along the cap. The clearance varied from 0.00075" to 0.0010" (that is 3/4 thousand inches to 1 thousand inch) Put it back together and the leak was still there. I drove it 2 mile to the bottom of the hill. I stopped and left the engine on to check for a leak. There was no leak. On the 9 degree grade it still leaked fairly bad. I noticed that the leak was worst when the engine was at idle speed. When I reved up the engine the leak would slow down from a small stream to a fast drip. After driving back to the shop, about 2 miles, the fast drip leak was still present.

Back to the shop. I removed the rear main cap again and did some more investigating. I found the the oil return pipe was sticking up too far into the oil channel in the cap. I cut a slot in the tube so the returning oil would not have to go over the tube that extended into the channel. Again by the owners request I cut a radial groove in the babbit 1/4" from the back of the cap and connected that groove to the hole that I had previously drilled in the middle of the cap. I measured the end thrust and it was 0.008". When I installed the cap I held it forward as much as I could. This reduced the end play to 0.005". I used some Permatex on the shims.

Back to the hill. I started with the oil level in the pan just above the LOW mark, one quart low. Again there was no leak after driving 2 miles to the bottom of the hill. But once on the hill the leak started again. When back on flat land the leak was still there but at a much slower rate. This time I drove it about 5 miles including about 2 miles at 55 mph. When I got back to the shop it was still leaking a fast drip. When the engine is shut off I do get the dump of the oil from the valve chamber which cause a momentary increase in the leak flow.

It appears that once the leak starts it continues even when on flat ground. I would think that any residual oil in the flywheel housing would be gone after driving 5 miles.

I am out of ideas short of tearing the engine apart.

help?

Bob
 
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Bob -
It sounds as if you're ready for another one of my "Why does everything happen to me?" true sob stories (or is that "S.O.B."?). I once had a Model B engine in the 1990's that was freshly rebuilt by a reputable builder. It leaked from the rear main bearing area as you described almost from Day One, whether on an incline or on level ground. VERY frustrating, as we could not find out why. Everything checked out o.k., as you have done. Drip, drip, drip.
Cutting to the chase, it turned out that one of the bores for the rear main bolts had been enlarged somehow enough so that the bolt shank was loose inside. This created
a path for the oil to work its way up the shaft and leak from beneath the bolt head. Really an oddball cause for leakage, but the oil was clearly coming out from beneath that bolt head. We could see it as the engine ran on a stationary stand with the flywheel housing removed and the flywheel spinning in open air. A little dangerous perhaps, but this was the only way we could track down the leak. We started the engine through a combination of a hand crank up front and by spinning the flywheel by hand, just like on the old steam tractors. The leaking oil streamed down the backside of the block, and once in the car, eventually through the flywheel housing hole at the bottom. It had all the signs of a classic rear main leak, which it only peripherally was. It was actually a rear main BOLT leak.
The solution was to remove the bolt, use two long strands of material peeled off a pan front donut seal and wrap them around the shaft of the bolt in that hole, starting just below the bolt head. This was coated with aircraft stickem shellac (like Indian Head brand) and allowed to set up. The bolt was then tapped down through the enlarged hole and more goop coated over the bolt head. For good measure, both bolt heads were coated. Everything was buttoned back up again and the leak stopped!
The Model B engine has a little more oil pressure than a Model A, but I see no reason why the same thing couldn't happen to a Model A engine, too. I have no idea how the bolt hole became enlarged or wallowed out in the first place, but it clearly was too big, even for a new bolt. To check this on your engine. remove the two nuts and the rear main cap itself and wiggle the bolts. If there is even the slightest movement, that's probably the cause of this frustrating leak.
By the way, I wrote an article about this problem and submitted it to "The Restorer" for publication. It appeared in a 1996 issue, whose date I can't recall. Photos of how to make the repair accompanied the article. Maybe if you can find the article, it will help you make the repair, assuming the enlarged rear main bolt hole is the cause of the leak.
Marshall
 
Marshall,

I had read your article while researching this oil leak. The bolts appeared to be tight. Unfortunately I did not try to wiggle them. But the cap was a little hard to install. I had to tap it up once I had it aligned with the bolts. With all the testing I must have taken it on and put it back on close to 10 times. In all those times the bolts did not move up at all. Also the cap fit was always tight around the bolts. If I take the cap off again I will try to wiggle them but I do not think they will wiggle.

I would like to add some additional information about the leak. When I was looking through the inspection hole with the car at an angle the leak was seen coming down the back edge of the rear main cap. I should have shot a video because describing it requires me to intemperate what I saw. It appeared to me that the oil was not coming from just the bottom of the rear main cap. I could see oil all along the rear edge of the cap. I could not physically see the back of the block above the cap so I do not know if there was oil coming out there. It also appeared the the oil stream became bigger as it move down from the top of the cap to the bottom. I was looking in at the drivers side of the engine. Again there did not appear to be any oil leaking out in the shim area, only at the back corner of the rear main cap.

Bob
 
In addition to the excellent info by James Rogers, you have a 3.5 degree angle on the engine as it sits in the frame.

I have had more than one case where a wad or partial wad was left in the rear main bearing oil drain passage. The purpose of the wad is to keep new babbitt from flowing into the oil drain when it is poured. Remove the plug pressed into the rear main cap to check that oil drain passage is clear.
 
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