Model B engine rear main oil leak

Bob Johnson

Bob Johnson

Well-known member
I am working on a Model B engine which has a huge rear main oil leak. The oil is leaking out the hole at the bottom of the flywheel housing where the cotter pin is located. It is not a drip .. drip. The oil is actually flowing out in an uninterrupted stream.

I have removed the horseshoe shaped inspection plate on the front of the flywheel housing. With a flashlight and mirror I found that the oil is coming out only at the rear of the rear main. There is no oil coming out at the front or sides (shims or bolts) of the rear main. With the engine running the oil flow out the back is so much that the oil squirts onto the front side of the flywheel. The spinning flywheel then throws the oil onto the sides of the flywheel housing and it then runs down and out the hole at the botton of the housing.

I have checked for excessive blow by and found none.

I removed the small return pipe which is on the rear main cap. It was not plugged and not up too far into the cap. The return pipe is the proper length.

I ran a wire into the gallery at the bottom of the rear main cap and it did not run into any obstructions.

My guess is that either there is too much oil flowing through the rear main or there is an obstruction preventing the oil from returning through the return pipe.

I can not check for an obstruction without removing the rear main cap and I can not remove the cap without removing the engine from the car.

I was told that prior to the recent installation of the engine in the car the main bearings were checked and any shim adjustment was made.

The amount of oil leaking was so much that it might be more oil than can drain down the oil gallery and out the return pipe at the bottom of the rear main cap. Does anyone know how much oil would be too much for the gallery / return pipe ?

What next ?

Try to blow air up the oil return pipe ?
Use a syringe to force oil down the oil passage from the oil pump to the rear main and see now much comes out the oil return pipe and how much comes out the rear of the rear main ?
Remove the engine and recheck the rear main ?

Bob
 
Bob ;
Had the same problem with my "B"engine . It either leaking from the main or cam shaft or both . Mine was both . Had to pull the engine . As it relates to the rear main ; The engine builder had jambed a chevy rope seal down in between the slinger and the rear main cap . The seal had disengrated into fuzz and the fuzz plugged up the oil passages . Cleaned all this out and put rear main cap back . I did notch the oil return line where it goes into the cap ( you can by an already notched line for a "B" engine) . JB welded the line into the cap making sure it was not screwed in too far . Notch should line up with oil passage in cap . As it relates to the cam at the back of the engine ; Builder had put a metal plug at back of cam . Cam moved back .caught the plug ,spun the plug which then ripped the gasket . Took out plug and then used silicone in lieu of gasket around fly wheel cover . Note silicone is thinner than the gasket therefore you may not need to put the shims back in . I put my shims in and had no problem .Also you need to silicone the threads on the bolts holding the main cap on as oil will leak around the threads . Also put a thin layer of silicone on the side of the main cap. The rear main babbit was ok and I did not need to remove any shims . Basically put the engine back together as ford had designed it . NO LEAKS !! Before I did all this I checked the horz . movement of the crank shaft . If the thrust portion of the rear main is broken the crank will move back and forth horz . acting as a pump and pump oil out the rear main . In any case you will have to pull the engine .

Good
Luck with it .
 
I never saw one leak this bad. If you pull the rear main cap make sure the oil groove doesn't extend to the end of the babbit. The same applies to the oil pocket formed at the parting line.
 
Duffy,

There was no leak at the end of the camshaft.

I also notched the rear main oil return tube. That did not help.
 
How much end play does the crank have. should be .004=.006 If much more than that it is going to leak. My guise would be to much clearance or to much end play.
 
I have found 2 things that will make one leak like that if the bearings are clearanced correctly. 1. Make sure the rear aluminum seal is in place. 2. I have found if the aluminum seal is not sealed in placeand the ends level with the block it will leak. I always put a little permatex #2 on the ends of the seal so if it is a little short it will seal.
 
Check the breather cap for being plugged up if so most of the oil will be forced out the rear main area.
 
I think the syringe idea is the only remaining option for further diagnosis. You have determined the site of the leak but cannot really see why it is leaking. Is this a stock rear main configuration? Is it possible that somebody has installed a non-stock seal, following removal of the slinger? It seems like you may have to bite the bullit and pull the engine to get a real assessment of this.

Last year I talked to a fellow that had acquired a Model A with a B-engine that performed nicely for several years. That is, until it suddenly started gushing oil out the rear main just like yours. It turned out that the previous owner had installed a neoprene seal when the engine was rebuilt. When the seal failed it failed all at once. With no seal and the slinger missing the oil had a straight path into the flywheel housing.
 
Bob, I have chased rear main leaks since I started with Model A's. I have found them in every way you can imagine and the new ways keep popping up. You will have to pull the engine and find the leak. You already know it is leaking and can't find the source so how would injecting oil into the rear tube help? You still won't be able to see any more than you can now. You can blow into the tube with compressed air but you will only be able to feel it come out but not where. Even if you can figure out where it is coming from and what to do to fix it there is a 99% chance you will still have to pull the engine to affect any reasonable repair. Looks like a hoist is in your future.
 
I have exactly the same issue on my Miller B in my 28A, the car had been barely used for about 5 years (Only started and run up and down the road). I re-commissioned it and now the oil flows out (Mine is pressurized and insert bearings).
Pulling the motor at the weekend, seemed like the only way to get the correct answer to the issue...
 
Bob ;

I had to pull the engine on my car in order to find that oil was coming from the back of the cam .
 
James,

Yes I agree however I would like to have more information before I take it apart. In the past I have taken things apart that were not working. Then found nothing. When they were put back together the were working again. It would be nice to know if there is an obstruction before removing the engine.

Another "test" I thought up was to run a rubber tube from the bottom of the rear main oil return tube down to the oil drain plug at the bottom of the pan. Then use a drain plug with a hole drilled in and run the rubber tube through the hole. This would allow me to see how much if any oil is returning to the pan. If there was little or no oil then that would suggest a clogged return tube or gallery. If there was a "normal" flow then I would suspect that too much oil is traveling through the bearing. I doubt I will do this.

Duffy - no modern seal

Bob
 
Last edited:
Duffy1 said:
Englishdavid ;
Do you have the modern rear main seal ?
Click to expand...

Duffy,

I don't actually know, the motor was built by Vermeil's Engines Only in CA in 96, put in the car in 97/98 but not driven any distance until now.
Anyone know if Vermeils is still going? - Quick search and Google search didn't bring up anything of use...
The written build sheet I have has some super hard to read hand writing...

Bob - didn't mean to Hi-jack your thread :-) Sorry
 
Why not pull the rear main and check things out? Clearences, shims, thrust face,oil grooves, and babbit as a whole? The rear main can be removed without pulling the engine. Support the crank when checking clearences. It is not the nicest work, you will get dirty, but it can be done.
 
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