VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Cam Bearing Cap/Plug

I have been trying to locate a rear main bearing oil leak and can not seem to resolve it no matter what I try. Now I am wondering if my oil leak is coming up higher on the block like at the cam bearing plug. I have not been able to find anything in prior posts and am wondering what is used for a plug in the rear of the block? How do you gain access to this area, I am guessing pull the motor? Is the plug like a freeze plug? What seals it in the block, just press fit? Is there a way to see if this is where the oil is coming from without pulling the tranny, clutch and flywheel? Thanks

Have you tried checking the back of your valve cover gasket to see if it is leaking? If the gasket is leaking the oil will run down the back of the block and at the lower end it will appear as though the main bearing is leaking.

Yes I have check the side pan and the valve cover very close no such luck.

The plug is a 1-5/8" steel concave freeze plug (NAPA has them under Part Number 381-1014). It is driven (expanded) into place during engine assembly. I think it's very unlikely to be the source of your leak, because unlike most of the other plugs, it does not have any contact with the coolant and is unlikely to corrode or to come loose. To replace it you have to separate the bell housing from the engine, which means removing the engine from the car.

In my opinion, the much more likely source of the leak is the rear main bearing itself. If you're SURE it's not the valve cover, then you should drop the oil pan and remove the cap from the rear main bearing. Check for blockage of the drain hole, which contains a small ball check valve in it and is easily blocked. Wash it all well and blow out with compressed air. Reinstall and check rear main clearances with plastigage, adjusting as necessary. (Excess clearance in the rear main bearing is the most likely culprit if the drain hole in the bearing cap is clear) Reinstall oil pan with new gaskets very carefully positioned, especially the cork strip between the oil pan and the rear main bearing cap.

Hope that helps. :vcca:

All the Best, Chip

Chip
I have checked and double checked the side cover and the valve cover. I have had the oil pan off three times now and still have not been able to find where my leak is coming from. I have plastigaged the bearing and am wondering if I just need to run it a while to seat the crank in the bearings and then reshim the crank bearing caps. I have a pretty big leak that is hard to tell where it is coming from since it hits the flywheel and is throw everywhere. I just got thinking about the freeze plug last night and was wondering if I could eliminate that as the cause.

Did you inspect the rear main bearing ball check valve as Chip suggested?

When you plastigaged the bearing what was the clearance?

My bearing clearance is .002 with the flywheel supported when taking the plastigage reading. I should mention that this is a 30 year old rebuilt engine that was never run. My check ball is gone in my rear bearing cap so I know I could leak some oil on a steep grade. The drain back hole is clear and in fact has been enlarged to allow more oil to drain back into the pan. I am running 30W oil at about 18psi. The vehicle has about 2 hours, 35 miles, on the motor. It runs good, excepet for a high speed miss(maybe weak valve spring?). I am trying to fix this oil leak before I move onto the next challenge. I do notice when looking at the rear bearing that I can see where the babit is slightly polished on the front of the bearing cap but not at all toward the back. I have two .002 shims in each side of the rear bearing cap. If I remove any more it binds up the crank. I have loosened the center crank bearing cap when setting the rear and will now shim the center since I can not take any more shims out of the back without the binding.

So, I take it that your rear main bearing oil leak is when you are driving the car...is that correct? Also, you mentioned that your oil pressure is 18 pounds. Is that also when driving with the oil hot?

Did you check the rear main for taper? If you use long pieces of plastigage or several small pieces to cover the front to back approximately 120 degrees apart (one set on the bottom and then around the crank (yes you need to get them onto the top half bearing), it will give a reasonably accurate measurement. If you loosen the center main cap the crank can be moved down a little so you can get the plastigage on the top. If the bearing or crankshaft is tapered it will lock up when shims are removed but can still leak oil.

I hate to suggest this but you may have a twisted or bent crankshaft. It is common to bend them if you don't handle the crank properly or try to turn over a stuck engine. It is best to try eliminate other possible causes first.

My oil leak is when it is running and is very small, if at all when at idle. When the rpm comes up that is when the leak picks up. My oil pressure is 18 lbs at idle with straight 30W when cold, it will drop to 8-10 at idle when hot. My leak also seams to pick up when hot. When I plastigage I have supported the flywheel and I have used one piece of plastigage on the bottom of the bearing cap. I think my problem could be a tapered bearing becouse it measures .002 on the front of the bearing but much more on the back of the cap which I think will force the oil out the back more than the front. I also notice that the bearing is polished on the front and no sign at all of any polishing on the back half. Since my motor is installed even if I could get plasitgage on the top I would have no way of seeing it after I torqued it. If my bearing is tapered what is the fix and how would this have happened? I thought the mains were poured babit but I see in the parts book is shows them as a part? Are the bearings forgiving on these engines? I have loosened the center bearing and adjusted the rear with shims until the crank wont turn then added one shim and I now have .002 at the front but it is looser, about .003 to .004 on the back. I wonder about trying a different weight oil? Should I try running it and maybe the bearing will wear on the front surface and after getting some miles on it I could pull the pan and remove shims? I am worried about damaging the clutch disc with all the oil flying off the fly wheel.

Okay, we know know the problem. If the rear of the bearing gap is over 0.002" or so it will leak oil. I would suggest scraping the front of the bearing so you get 0.001" without the shims. That should get you ~ 0.002" on the rear of the rear main. That should stop the leak or at least reduce to a manageable level. It can be done in the car with much difficulty. Scraping the top must be done without seeing what you are doing and with a thin sharp blade after dropping the crankshaft down to get a big enough gap. Best to remove the engine and do the job correctly.

Chipper
You have supported what my thoughts have been. I think if I had a taper but the tight side was on the back of the bearing it would not be an issue. I beleive you are also saying that the bearing are much more forgiveing than a newer bearing if I can just scrape some material off to get my clearance. I was thinking about maybe getting some fine emery cloth above the crank to see if I could somehow sand down the front half of the bearing. I also agree it sure would be better to pull the motor. If I decide to do that how do I get the motor up enough to have the bell housing clear the sub frame? It looks like it would hit the firewall before it would be high enough to get the motor forward.
Thanks again you guy's are very helpful. This older stuff is all new to me but I am really enjoying getting to know a little about them. I am doing this car for my older brother who has had some health problems lately and he is there every night "SUPERVISING" which has been very good for him. I actually have got about 40 miles on the car so far and was able to have him go for a short ride. He bought the car over 40 years ago and it has not been on the road since he has owned it.

Sanding off the front of the bearing is an idea that I had but don't recommend. The reason is that some of the abrasive material can be loosened and embed in the babbitt. It might not happen but I can't in good conscience recommend it.

You are right if the taper was wider in the front you would not have the problem.

If you remove the top cover from the transmission and then lift the engine/transmission straight up the front of the oil pan will clear the front crossmember and the flywheel cover will just clear the second crossmember. I always use a pad or cardboard between the back of the block and firewall to protect the paint.

An oil leak at the rear of the crankshaft is already a popular subject for the owners of old car. I had this trouble with my chevrolet 1932. The engine had been rebuilt by a machine shop that rebuild moderns engines.

I didn't try to cut cost. I put many new parts NOS i.e. main bearing ,connecting rods, pistons, valves, all the kit. The crankshaft was ?metalized? at the standards measurements and a line bore was made in the block. Even after that, after each ride, I had a big oil puddle under the engine. All adjustments have been respected excluding the gap between the oil slinger on the crankshaft and the oil trough in the block. The maximun at this point is .032 and I had more than .110. When the engine was dissembled the central main bearing flanges were totaly worn out. The crankshaft end play was huge and the oil slinger scrubbed the oil trough edge and made a bevel.

I corrected this and after many rides and over 1000 miles I have no more oil lost.

Today's mecanics are used to work with seal and are not aware of this crucial adjustement.