VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 39 engine rear main seal

I have a question about my 1939 motor. I have recently had it professionally overhauled. Since this was done I have an oil leak from the rear of the crankshaft. When first overhauled it leaked when standing and idling. The guy that overhauled the motor came out, removed the sump and then removed the small ball from the the rear main bearing cap. The motor now leaks only when being driven as the oil surges. I am going to replace this ball and see if this cures the problem. However it appears that I have ring bypass and this is pressurisng the sump. The overhauler seems to think the rings may eventually bed in and stop pressurising the sump. As the engine only has a slinger ring on the end of the crankshaft the guy that overhauled the motor now wants to put a convential seal here. He wants to know if anyone is aware of this modification being made and what seal would you use. He has the machinery and workshop to perform the work. Any replies and thoughts about the sump pressure would be appreciated.

While anything is possible I have never heard of a seal being installed in a pre 1940 engine.
I would suggest replacing the ball. I assume all other parts are correct, etc.
I assume that the crankcase breather pipe is not restriced....fumes should be seen coming from the lower end of it at a hot idle speed. (this is normal). I would doubt if piston ring "blow by" is the problem.
The first thing I would suggest is to check the clearence of the rear main bearing. Either remove shims until there is drag when turning the carnkshaft and add one shim....or place a jack under the rear of the crankshaft and check the clearence with Plastigage.....should be .001". More than .002" will allow too much oil to pass through the bearing.

When all else fails this is what I did. Following an "old timers" trick ....Remove rear main bearing cap, using two hack saw blades side by side cut a small trench in the lower half of the bearing from the oil grove forward. I did not do this at the very bottom where the shaft pressure is but to one side, about an inch from bottom center. Made the trench about .030" deep. After abot 25 years and several attempts this was the only thing that worked. (would still check the bearing clearence)
I have driven my '39 several thousand miles at high speed since doing this and still no leaks and no other problems.

Chevgene

Will check with overhauler. He did state when he removed bearing cap that clearance was as per specifications. I can't recall whether he said 1 thou or 1.5 thou. I will check with him. He is currently away for about 2-3 weeks from today. Breather puffs slightly when running and a few drops of oil drip from the breather when you return from a drive. In meantime will replace ball and see if that cures the problem. By the way engine has new slipper main and big end bearings along with new pistons and rings. Compression test reveals variation from 125psi to 140psi between cylinders. Motor pulls and goes well with no noise or smoke, just this annoying oil loss. Leaks about 1/2 pint in 100 miles.

No oil should drip out of the breather . There is a baffle inside the block covering the breather opening in the block so no oil can be thrown against the opening.
Seeing it is puffing indicates the breather open and working and reliving crankcase pressure.

Actually the ball prevents oil loss in the car is parked on a steep hill and the oil is full and raises up to the return passage. If it were mine I would want it in place,
The compression is certainly high enough. Usually only 110 to 120 for that engine.

I would call that excessive leakage. I assume that you have check for other possible sorces of leakage such as the back of the rocker arm cover and the back corner of the push rod cover.

Chevgene
Have so far resealed sump twice, rocker cover once, sideplate is Ok. Have removed gearbox and checked rear of block and bell housing-found 2 bolts missing from bellhousing-replaced and sealed-all to no effect. Managed to talk to engine overhauler late today who stated that he set the main bearing clearance at .002 inch, as per overhaul instructions. Baffle is in place in engine breather, however as stated a few drops of oil are leaking from here and when cap is removed it is wet with oil. Will remove sump either tomorrow or on saturday and replace ball in bearing. Will probably also try your old timers cure. At this stage I am willing to try anything. Engine overhauler said if this all fails he wants engine back and will pull apart at his cost and fix. Thats if he can fix the problem. Mind you its a few days work again for me to remove and replace engine.

Gene
Sorry it has taken so long to reply to your ideas. Have had a few family problems since last communication.

Anyway finally removed main bearing and on testing with plastigage found that clearance was .003" to .004", not .002" as stated by engine overhauler. I ended up removing both shims that were under the bearing cap and now have a clearance of about .00125". I also replaced the ball in the bearing cap and used your 'Old Timers Trick' as well by putting the grooves in the bearing shell.

It now appears that I have no oil leaks after driving the car for about 30 miles this morning. I hope that the oil leak has been cured and keep my fingers crossed. Now if only I can fix that sticking throttle.

Thanks very much for your suggestion and help. It was very much appreciated and supersedes any advice I have been given here in Australia.

Glad to hear back from you. Keep me posted.
I would suspect the sticking throttle problem is caused by the complicated linkage for a RHD car.

In you last post, you said that you removed shims from the rear main and that seems to have fixed the problem. Question, what about the other 3 mains? If he didn't get the rear main right, may have made same (or worse) error on the others. If so, with rear main adjusted correctly and the next one wrong, you can put a bending on the crankshaft and potentially stress to the point of cracking it. Have had it happen to me.

Yes, the clearence of all the mains should be checked.

I had thought of this problem this morning and spoke with a friend who is an old motor mechanic and actually owns a 1938 sedan. He was of the same opinion that after all the troubles with the oil leak, would it be worth the effort to remove the sump again and remove each bearing when there may only be at the most .002" difference between the wrong and right clearance for these bearings. Also at this stage I need the car for a wedding next week.

The question also arises as to how accurate the crankshaft has been reground and whether the block was line bored or not. I will have to talk to the engine overhauler again and question him as to how much work he did to refit the crankshaft. I am aware that the crank had some rust on it and we had to fit .040" oversize bearings. The other point is that the engine runs perfectly, with no noise, good power and continues to power up hills.

At this point in time, after so much time and expense, in fixing this engine I will possibly wait and see. The dissappointing part about the whole matter is that I used what was supposed to be an expert? rebuilder of old motors. When taking on the job he said that if he overhauled and re-assembled the motor he would guarantee his work. His only response so far has been for me to bring the motor back and he will fix it. There were no offers to help me remove and replace the engine, nor even come to my place and help, except the one and only time he removed the ball from the bearing cap-something that I now beleive was the wrong thing to do.

If I remove the other bearing caps and find they are OK, where do I stop with checking his work.

A rather imperfect test for the other mains is do you hear a distant rumble or slight deep knock when starting the engine after it sits for a length of time?....This will lat for only a second and disappear as soon as oil is pumped into the main bearings. At about .003" they will commonly do this and in its self is nothing to worry about.

ball in main bearing cap? What's this about? didn't see one in mine. Don't have the pan on yet, should I take the rear main cap back off and cut groves in the bearing? Hope i'm not overlooking anything else.

The ball is in the oil return passage that runs from the deep gutter that the slinger throws the oil into so the oil in the gutter can return to the pan. The ball can be seen in the hole facing forward on the cap. (front of the cap) There should be a pin to prevent the ball from falling out. The opening gets slightly smaller so as to have the ball roll back and block the return hole so if the car is parked on a steep up-grade the oil can not drain from the pan and run out the main bearing.
Often the ball was removed to "fix" the leak, the thought being the ball was obstructing the path for the oil to return to the pan. From my experiance the leak will be the same either way. One exception would be if road draft tube is plugged with sludge and the engine has a lot of blow-by , building up crankcase pressure and pushing the ball back and closing the opening......This pressure is harmless but if the breather pipe is restricted it can cause the problem.
Cutting groves in the bearing....thats up to you but it worked for me.

Thanks Gene
I'll check it out.

If it was my engine I'd check the other bearings when time permits as Gene suggests. As far as second guessing the rest of the work done to your engine I'd run it some, and do normal checks and maybe reset the valves after a few hundred miles. Maybe even re-torque the head bolts. Just drive, enjoy and listen. Good Luck Don

I agree with what Gene says about checking the other bearings, however I am at this stage prepared to also use his advice and continue to check for any unusual noises in the engine. At the moment it is a very quiet motor, with exceptional performance.

I had intended at 500 miles to re-torque the head and reset the tappets (valves). I will just wait and see as we need to use the car during the next few weeks.

By the way I fixed the sticking throttle-it was caused by a nut on the throttle crank jamming on the accelerator pump linkage. (It is a tillotson carburettor).

Anyway I would like to thank everyone for their advice.