VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Oil leak back of crankshaft

Hi, I am very new at this. However, I did have a 1936 Chevrolet coupe 25 years ago that was a hot-rod. I recently purchased a 1931 Chevrolet sport roadster six wheels.

My immediate problem that I need assistance and guidance on is that there is an oil leak at the back of the crankshaft. When the car is stopped oil will leak from the fly wheel for a period of 5 to 10 minutes and then stop. I have several manuals but now of them indicate the problem or how to solve it. They don't indicate what kind of seal is there. Is the seal one that has to be tighten a little to adjust it? Does it have to be replaced? Are there options in replacing the seal. And the big question is how do I go about taking everything out to get at the seal? Or are there special tools to deal with the seal? I am very appreciative of any advice that anyone has to give.

My information on the car is that it is all original and in good condition. So my assumption is that everything on the car is 1931 with the exception of a view minor items that have been repaired over the years. My goal with the car is not for show, but for the enjoyment of driving it. I want to keep the car as original as possible but within reason.

There has been some woodwork done around the seats. The interior is a red leather. The ignition switch has been replaced with something more modern. The motor I am told has been rebuilt, but the car hasn't been used for quite a few years. Other than that the car appears to be original. I will be getting an appraisal and I will get more information at that time.

Thanks for your help

Welcome to Chevy Chatter II!

There were no seals used on the front or the back of the crankshaft in 1931.....only oil slingers.

How much oil are you leaking? A few drips after running the vehicle is normal.

:) :grin:

It leaks a puddle that will spread about 1 ft in diameter. What is an oil slinger?

That leak is extreme.

An oil slinger is a round device that is part of the crankshaft in the rear and it kinda sorta takes the place of an oil seal.

There could be several different reasons why your engine is leaking that amount of oil from the rear main area. There is a check ball in the rear main bearing cap that allows the oil to flow into the oil pan. If that ball is stuck in the up (or rear) position, then oil cannot return to the oil pan and it will drip on your garage floor.

Another possibility (and this is an easy fix) is that the rear portion of your valve cover gasket is leaking. If so, the oil will run down the back of the block and drip out the flywheel area making it look like a rear main leak. You might want to put your hand down behind the back of the block, just below the cylinder head, and see if there is excessive oil at that location. If so, then your valve cover gasket is leaking.

:( :cry: :grin:

Ok, I'll try the easy route first and I'll check carefully to see if there is a casket leak. If it's the other problem how do I check that and or repair that. I'll let you know what I find.

If you don't find a valve cover gasket leak then you will need to pull the pan and take off the rear mail cap. Check the cap to see if the ball is in there and free. Blowing air into the hole in the groove will tell quickly if that is the problem. If it is ok then the rear main has too much clearance and needs to be tightened. I will not go further until you get more information.

I had the car running today and I checked the the valve cover gasket. Everything is bone dry and clean. So it appears that I have to dig deaper for my solution. Any details about what I should do?

From Chippy Dippy's posting above:


:) :cry:

Hey guys does a '30 have this "ball" in the rear main? I rebuilt my motor about 20 years ago and can't remember any "ball". Mine doesn't have a leaking problem but just wondering about the "ball". Thanks,Stan

Yes, it sure does......unless it was removed years ago.

:) :grin:

Hey Dawg, Where does it go and what's the purpose of it?

Hi Stan! The check ball is located in the rear main cap and the purpose of the ball is to roll backwards and block the oil return hole in the rear main to keep the oil in the pan when the car is going up a steep hill.

:o :/

WOW !!!, I don't remember my engine having one. I guess when I start driving it I will find out. Thanks for the information!

Maybe someone removed the check ball years ago. Some dudes take the stupid ball out since it is almost worthless anyway.

Hi and welcome to the Forum...I had exactly the same problem with my '39. I agonized over that oil puddle every time I shut the engine off for years until I finally figured it out myself by taking a deep breath and removing the oil pan to see what was happening. There were two bolts holding on the rear main cap. I forged ahead and took the cap off to look for a seal, but found that there is no seal, but there should have been a loose check ball in the cap that plugged a hole when the engine was shut off. I found a ball bearing (at the hardware store) the right size. A pin was used to hold the ball bearing in the cap that was also missing. After putting the ball bearing in the cap, I replaced the pin with a nail shaft to hold the ball in place. You'll see all this when you get to the cap. It just takes time. That stopped all the oil leak. The hardest part was replacing the oil pan gasket so that didn't leak. I hope you have a warm garage to work in. We learn as we go.
Best wishes,
Chuck

On the early six cylinder models the check ball does not plug a hole when the engine is shut off. Actually it is intended to roll backwards to the "up" position to the back of the main bearing cap to keep the oil in the pan when going up a steep hill. If the check ball is either missing or in the "down" position then the oil will flow into the oil pan and there should be no leaks.

:) :grin: