Rear Main Leak – Bear with me

[spinelll]

I’m trying to use process of elimination on my rear main leak.

Crankcase vent is not blocked.

I dropped the oil pan and took a little bit off the threaded end of the small oil drain tube that runs from the bearing to the oil pan.
I wanted to ensure that when fully tightened, that the tube was not breaching the cap and restricting return oil.
Buttoned everything up and ran at idle for 30 minutes. No leaks.
Then I increased the RPMs a bit and ran at that higher idle for about 15 minutes after which, there was some oil dripping from the cotter pin.
Then I took the car out for a spin (15 minutes?) and, just as prior to removing the pan, oil was finding its way down the middle of the half-moon inspection plate and also at the cotter pin. So I’m sure the oil tube is not the issue.

I keep the oil level just a bit above the LOW mark. But then I read where if the oil tube is not actually submerged, crankcase pressure can push oil up that tube.

What else can I check? If I idle the car with the inspection plate off, will that reveal anything?

It’s really frustrating. Every time I take the car to a buddy’s place, I either have to park in the street or bring shags of cardboard. It’s enough to make me consider selling it believe it or not.

Thank
Leo

[BRENT in 10-uh-C]

Excessive end thrust is always a culprit, -or even excessive journal to cap clearance.

[Y-Blockhead]

Before you sell it are you sure it is a rear main leak? My Town Sedan had a leak and I was about to pull the pan. But first I installed a bottle of fluorescent dye and checked with a UV light.

After running the engine I could follow the 'glow' back to the oil return pipe. Saved me from pulling the pan.

On another engine I checked it was obvious that it was the rear main. The inside of the flywheel 'glowed'.

Hope this helps and good luck.

https://www.amazon.com/Interdynamics...QN4TQJK0TM6F7Ror available at most auto parts stores.

[Benson]

The bolts that hold the front timing cover on will leak if you use split lock washers.



Most leaks happen on bolt holes that are open to the inside of the engine.



There are 6 or 7 (9/16ths head) bolts that come in from the front and the two that hold the side timing cover on.


Do not forget the one bolt in front that is hidden inside the cavity near the generator mount.



I remove the washers and apply some Ultra Black sealer to each bolt head (and threads for good measure) where they contact the cover.


If oil is leaking it runs down the bottom of the oil pan rail where the 1/2 inch bolts fasten the pan to block until it finds its way to the flywheel cover.... the passing air moves the oil along pan rail.


The clue is that oil drops appear on the pan bolts even after you replace the pan gaskets.



Looks just like the rear main and or the camshaft hole at rear of engine under the flywheel cover is leaking.

[Chuck Sea/Tac]

There is always the chance it’s the rear of the cam shaft. Pull the three bolt inspection cover on the bottom of the fly housing and run the engine. You can look up at the outside of the rear main cap and see if it’s coming out of there.

[Charlie Stephens]

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What is the last thing you did before it started leaking or was it something that increased over time. The reason I ask if you just had the engine out did you replace the gasket between the engine and the flywheel housing?

Charlie Stephens

[WHN]

Do you have a “leak”, or is your car just marking it’s spot?

We can sometimes try to make things to perfect. Never had a Model A or a Jaguar (pre 1960), that didn’t leave a spot or two. Enjoy.

[spinelll]

In no specific order:
1. I had already Permatexed the pan bolts in the timing cover.
2. No leaking from the oil return outside the block.
3. Definitely leaking, not spotting.
4. Didn't have the engine out. Increased over time.
5. No dripping around the other pan bolts.
6. A little oil from the front seal but I think that's from having soaked it first.


I forgot to mention that I have a pressure system.

[gconner]

I took about 5 thou off the rear main cap by rubbing it on a piece of plate glass with wet and dry paper soaked in wd40. Checked afterwards with plastigauge to make sure it wasn't too tight. Now the only oil coming out is from the shafts in the gear box housing.
Cheers.
George from Australia!

[Railcarmover]

Leave that oil leak at the front shift shafts,it lubricates the wishbone ball.My engine has a vent at the upper rear of the valve cover along with the filler vent.I assume it was put in to insure atmospheric pressure in the valve chamber,don't totally agree with the theory but I left it just the same,cant hurt.

Pressurized? pressurized main bearings? model a or b? insert bearings?

[BRENT in 10-uh-C]

Originally Posted by spinelll

In no specific order:
1. I had already Permatexed the pan bolts in the timing cover.
2. No leaking from the oil return outside the block.
3. Definitely leaking, not spotting.
4. Didn't have the engine out. Increased over time.
5. No dripping around the other pan bolts.
6. A little oil from the front seal but I think that's from having soaked it first.


I forgot to mention that I have a pressure system.

As mentioned in post #2 above, excessive clearance is going to be the #1 cause of this. Even if the journal to crankshaft pin clearance is within specs, having too much end thrust will cause that on a stock splash system. Add a pressurized oiling system to the equation causes this to be exacerbated because there is nothing to slow the oil flow down. If the thrust end play is much over 0.006", you are going to have a leak.

[Benson]

deleted and PM sent

[spinelll]

Originally Posted by Railcarmover

Leave that oil leak at the front shift shafts,it lubricates the wishbone ball.My engine has a vent at the upper rear of the valve cover along with the filler vent.I assume it was put in to insure atmospheric pressure in the valve chamber,don't totally agree with the theory but I left it just the same,cant hurt.

Pressurized? pressurized main bearings? model a or b? insert bearings?

Main bearings
Model A
Babbitt

[denniskliesen]

Did you put sealant on the bolts where the holes go through at the back of the block? At least one goes through near the camshaft. Oil will leak through the threads and lock washer causing a leak. Another place you could have a leak is where the aluminum seal is on some of the aluminum seals had a gap that the main bearing cap left a gap allowing a leak. Especially noticed when engine shut off. Sometimes the shims will cover it and not be able to see and allowing oil to leak from between the shim and the block. You could also have oil leaking from the bolts holding main bearing cap. If the small freeze plug wasn’t removed from the main cap there could be a restriction where the tube goes into the main bearing cap. Too short of a tube on the main bearing cap can cause a leak. Here’s another place, the bolts going in the corner of the oil pan go through the block, seal those also.

[Jim Brierley]

With a pressurized system you should have a seal on the rear of the crank. A pressureized oil system puts more oil to the bearings than the stock gravity system. I recommend the Burtz 1-piece seal. In the old days we just used a rope-style seal, those work but don't work well forever. Oil can also leak from where the cap meets the block, and from the top and/or bottom of the main bolts. Y-blockhead and Brent's comments are very good. Good luck!

[CT Jack]

I had a similar excessive oil leak experience immediately after my engine was completely rebuilt. As I was going throught he break in period it looked as thought the area around the rear main was leaking badly. Notice I didn't say main seal because the Model A doesn't have one. After removal of the engine and returning to the rebuilder, the engine was disassembled and rechecked for possible causes for the excessive leaking. The problem was directly related to a large clearance (.020") between the bell housing and the back of the block. As has been mentioned in several threads the rear of the cam that rides in the block does not have a seal. Any gap between the bell housing and the block will allow oil to leak by. The bell housing mounting face was blanchard ground and reinstalled. No more oil leaks.
This might be the cause of your oil leak.

[stewgee]

Originally Posted by Chuck Sea/Tac

There is always the chance it’s the rear of the cam shaft. Pull the three bolt inspection cover on the bottom of the fly housing and run the engine. You can look up at the outside of the rear main cap and see if it’s coming out of there.

Never thought of that. Interesting idea. My leak is not that bad, just annoying. Drips on the shop floor.

[Railcarmover]

When was the modifications to the system done? do you have any recourse with the builder?

[Purdy Swoft]

The aluminum, (so called seal) at the rear main bearing can cause a bad leak if pushed TOO far down into the block !!! The ends of the aluminum seal must be level with the block on BOTH sides or a gap will be created . I don't cut or shorten the front rope seal . I agree that too much clearance between the journal and cap is the main cause of rear main oil leaks . I set the clearance at .002 two thousants on the mains and rod bearings . I seal the oil pan gasket to the block . I make sure that the rear cork seal is properly sealed on top of the pan gasket where the gasket inters the groove in the rear main bearing cap . I would recommend the rear main bearing bolt kit that is mentioned in another thread . The seals in this kit seals the washer to the bolt instead of sealing the washer to the block . The times that I did everything else in this thread , I still got drips until I installed the bolt kit . The bolt kit is expensive but well worth the price to me .

[spinelll]

Here are 2 pics.
I took the inspection plate off and ran the engine. I didn't see anything special other than the oil on the left cap bolt. Nothing spitting with the engine idling.

On the pic where the inspection plate is on, I've highlighted where most of the drip occurs.