I have been looking into a rear main oil leak for a couple of nights. I can not see where the leak is coming from other than dripping of the front flywheel cover. It does not leak much when the rpm is low, when I increase the rpm the leak becomes almost a steady drip. I have read all the posts I can find butam still not sure what my problem is for sure. I hate to pull the pan if I can not say for sure what is wrong. My oil pressure is 8 lbs at idle and increase to a max of 18 at higher rpm. Does anyone know where I can get a good picture of diagram of the rear main cap? I have read that it has some sort of drain back hole and a check ball for something? Any help that can be offered would be greatly appreciated.

There is an illustration of the rear main cap in your 1932 repair manual. It shows how the ball check valve works. Also, have you checked to make sure your leak isn't coming from the back of your valve cover gasket? If that leaks it will usually have the same appearance as the rear main cap leaking.

You mentioned that you have 18 pounds of oil pressure while driving. If that is a "hot" reading then you might too much oil pressure.

Dog
I will look again at my manual, I did not see a good illustration. Is it in the repair manual for a 32? My oil pressure is 18 at higher rpm with straight 30 weight oil. It is a fresh rebuild that I did not do, it was done by a college auto tech department. I do not know if it has a new oil pump or not. I the pressure is to high why would it be leaking out of the back of the engine? Wouldn't it be force out that check valve, which I assume is used to regulate oil pressure, and then back into the pan?

Dog
I forgot to mention I have looked very close at the valve cover gasket and the side pan gasket. I did have a very small leak in the rear lower corner of the side pan gasket.

The main bearings in 1932 were directly fed by the oil pump. As you increase engine speed the amount of oil fed to the main bearings also increases. So if there is too much gap in the rear main the flow can be more than the drain passage can handle and then oil will exit out the back of the engine. I would bet that the rear main has greater than 0.002" gap and therefore leaks.

The ball check is used to prevent oil to drain from the oil pan out the back of the main bearing if the vehicle is parked on a steep uphill grade.

I checked my literature and I found that the illustration of the rear main bearing cap and the write-up explaining how the ball check valve works is actually in the 1930 Chevrolet Engineering Features.

Dog
Is there any way you could email or fax that info from the 30 manual, I do not have tha manual.

Chipper
Is the best way to check the gap with plastigauge? I am a little worried if that is what is wrong with my rebuild most likely was not done very well and I will probable have to pull the motor to check crank and rod clearances to do it correct this time.
Thank both of you guys for the help so far, these older Chevy's
are all new to me.

Hi everybody here!
Question: It was told about a high oil pressure. Maybe his engine has a new modern gear-type oil pump as sold by Fillingstation and other shops. I guess the old original vane-pump can never make 18 pounds oil pressure. As it was explaned, 18 could be too much, an oil leak could be just because the modern gear-type pump pumps too much oil and the backflow-canal inside the rear main bearing could be too narrow to manage all the oil.

So, does that mean, it is not a good idea in general to replace the original vane-pump with a modern gear-pump?


Stefan germany

I had a later gear type oil pump in my '34 (same oiling as a '32).....Would hold about 18 pounds , hot 10W-30 oil, at 50 MPH....and I had no leaks.
There is something wrong with the rear main bearing and it will be necessary to remove the cap and inspect. If Plastigage is used the weight of the crankshaft must be supported (no weight hanging on the bearing) or you will get a false reading,
With a fresh rebuild I would suggest a lighter oil or at least 10W-30 ...for better flow when cold.
Camshaft plug at rear of engine leaking?

I don't have a picture of a diagram but I do have a number of photos of a rear main bearing cap:

photobucket 1

photobucket 2

Let me know if there is some other photo you need.

I think that you can purchase a copy of the 1930 Chevrolet Engineering Features manual from the Filling Station.

Well I pulled the pan and rear bearing cap. I plastigaged the rear bearing measure .002. I did drill out the return hole in the cap. When I looked at the hole close I noticed it is tapered, smaller at the slinger groove than toward the front of the pan. I did go ahead and drill out this return passage. There is plenty of material so I could see no harm in opening it up to allow more oil to be able to flow back. I have reinstalled the bearing cap and am waiting on the pan gasket set to see if I solved the problem. Would I be better using a lighter weight oil which should flow back the return eisier or would that also push more oil through the bearing? One other question, what should I torque the cap bolts to?

You could remove a shim and reduce the clearance slightly. Thinner oil would return faster but would also be pumped through the bearing faster.
Either way if it is leaking a steady drip it more of a problem than the oil or clearance.
I would suggest about 60 to 70 Ft. pounds for the main bolts.

The hole is tapered to allow the ball to close off the hole when it is in the up position. Did you drill the hole straight? If so then that will override the purpose of the ball check valve. Many dudes just clean out the hole and remove the ball, therefore that eliminates the necessity to drill out the hole.

I did not have any sort of a check ball or spring. It was a tapered hole, larger toward the front of the engine smaller toward the rear. How would a check ball and spring stay in the bearing carrier? Also how would the ball ever open to allow oil to drain into the pan? It is not presurized from the oil pump it is just a return for the oil that gets through the bearing I think. Does anyone know how thick the shims are that are between the cap and the block?

The ball check valve sits at the front of the hole in the main bearing cap and it is held in place with a vertical pin in the main bearing cap. There is no spring. When the ball check valve is in the front of the hole, which is the open position, the oil flows directly into the pan. If the car is parked on a steep grade then the ball rolls back to the tapered part of the hole thus blocking the hole to keep the oil in the pan from running out.

The thickness of the original shims were .001" and .002" with four of each used on each side. Removing one .002" shim will decrease the bearing clearance by .001"

You did have a jack supporting the weight of the crankshaft when using the Plastigage????

Plastigage is only appropriate to get an approximation of the gap. The weight of the crank will effect the amount of crush on the plastic. It is a good way to determine the taper in the bearing. By taper I mean the change in gap from front to rear of the bearing surface. Because the crank shaft twists and bends slightly as the engine runs it is common for the bearing surface to have more wear in the front and rear.

The repair manual gives the recommended method to set the bearing gap. Basically it is to remove shims until the crank will not move. Then add back shim(s) until it just rotates. That will give a gap of 0.005" to 0.015" which is what is needed.

That makes more sense, I was trying to figure out how a spring loaded(which I thought someone mentioned when I search this topic) was going to work. I do not have a ball and may not put one back in since I will not be driving this vehicle thousands of miles. I'll just never park on steep grades, or if I do I'll face down hill.
When I plastigaged I just remover the rear cap so the crank was supported by the front and center main caps, would that give me a false reading?

yes = support the crank its self

My rear carrier has 3 shims on one side and 4 on the other, is it acceptable to have a different number on one side? If I have to check for binding of the crank I will have to pull the motor to check that way.

Its acceptable to have one more on one side than the other. They advise to keep the most on the camshaft side.

To check the "binding of the shaft" you can remove two shims and see if it takes more effort to turn over the engine (try to turn it over before hand to get a feel). If two make it more difficult to turn install a shim. When completed it should turn over with the same effort that is required now but the removal of one more shim should make it more difficult to turn.May be necessary to remove more or less than the amount I suggested and the spark plugs must be removed for the above operation.

Well I got it back together tonight and have DRASTICALLY reduced my oil leak. I ended up enlarging the drain back hole slightly and removed one shim from the rear main bearing cap, I now have three shims on both sides. I looked at the drain back hole and I do have a hole above the hole but it looks like it is full of lead, I am guessing when the new bearings were installed. I am not sure what type of pin held the ball in becouse if it were a roll pin there is no way to get it out other than drilling when installed. I would think it would have to be tight in the hole since you would not want it to move up and contact the crank journal. The only time I had any leak was after I pulled the car forward a little quickly then I got a small leak about the size of a golf ball. hadguess is it was sloshing the oil back in the pan and with no ball it could leak out the hole. Now I wish I had found a ball the right size and what pin keeps it in. I may try running it about 1/2 qt low on oil and see what happens.

The vertical pin that kept the ball from falling into the oil pan was a round solid core metal pin.

Was it press fit into the bearing cap? And if so, how would it come out since there is no hole through the opening that the ball sits in? I have lead the hole, I guess I could try and clean it out and find a ball and pin. I don't want the pin to be able to work up and make contact with the crank.