Confused and Concerned about Rear Main Leak

Idaho Brett

Idaho Brett

Member
Finally got my Model A Running and Street Legal. But it leaks a lot of oil from the Cotter Pin below the Flywheel Housing when I drive it on the road. It does not leak when just idleing in the garage.

I dropped the Oil Pan to take a look at the Drain Tube that several people have talked about on other posts. I bought a drain tube from Snyder's hoping mine was missing, but there it was.

I compared the two tubes and my new one is about half an inch longer than the one I took off. (See Picture at end of Post)

TWO Questions:
1. Could the shorter tube cause the leak?

2. Is there any thing else I should look for while the Oil Pan is off before resigning to the fact I have bigger problems?

Thanks.

 
1930artdeco said:
Have you noticed the threads are different.

Mike
Click to expand...

I noticed that also.


Rear main leaks are cause by a lot of things. Number one to much crankshaft end play. To much clearance in the rear main bearing. Main cap not flat. Leaking around rear main bolts. Shims not in place. Leaking around rear slinger seal. To much crank case pressure. Drain tube plugged. Drain tube blocking drain hole. Babbitt in inside drain in rear main cap. Plus some I forgot. Also a lot of time you find it is the camshaft rear bearing that is leaking. If you do not want a leaker you have to check all this before you put it to together.
 
here is a good treatise on this problem linked below. Bottom line: its not always what you think it is. Check everything.

As long as the pan is off, check your main bearing clearances If the ctr main is loose, the flexing crankshaft acts like a pump, pumping the oil out the back. So check it too, even if it is a pain in the rear.

A very common cause is that the tube is screwed in to the cap so far it dams up the oil flow. Measure the # of threads into the cap and compare to the cap, then cut a "V" in the back side of the tube, leaving enough threads to catch the main cap, but none to occlude the channel so the oil has a way down and out the main channel. Be sure to tack the tube with a small MIG or TIG weld to secure it. Don't heat up the babbit so much it melts.

http://www.antiqueenginerebuilding.com/REARMAINLEAK.html
 
Snyders sells a thing called a rear main janitor. It bolts to the bell housing and catches the oil drips from the rear main. I got one for my full pressure B engine that tens to leak a little because of the oil pressure. Works great.
 
The rear main janitor works well, but you have to remember to empty it periodically. Since oil does not evaporate, the rear main janitor will gradually fill up. Then when you go around a corner, the oil will spill out and put a nice oil line down on the road for a short distance
 
have you checked to see if it is actually the rear main , or maybe the cam gasket between the motor & clutch housing .
 
the whole concept of a design where any part of the rear main bearing is placed outside of the engine pan sounds bizarre to me.....I believe the Company changed that design after the Model "A", didn't it?
 
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