VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 1931 Chevy Oil Pressure

My 1931 Chevy engine has the original van type oil pump. The oil pressure runs about 7 pounds at idle and may hit 10 at 30 MPH. Is this about what I should have? It seems low. Also, when the engine is running I have oil leaking out from the back of the motor on to the floor.

For a vane pump your oil pressure sounds good to me.

On the oil leak, the easiest thing to check first is the back of your valve cover gasket. If it is leaking the oil will run off the back of the engine onto the floor. There are other possibilities as well, but the valve cover gasket would be the first thing to check.

:) :grin:

THANKS, I have checked the valve cover and it is not coming from there. It seems to be coming from somewhere behind the bell housing. Do most owners of 1931 Chevys with the original 194 CID engine upgrade to the gear type oil pump which, I assume, produces more pressure? If so, what needs to be done to upgrade other than changing the pump? I have a feeling that the engine is going to have to come out.

The next thing to check would be the check ball in the rear main bearing cap to make sure that the ball is in the down position and that the oil passage behind the ball is clear. To do that you will have to drop the oil pan. The clearances on the rear main bearing could be excessive as well.

Basically, all you need to do is change pumps if you want a gear type of pump. In that engine oil pressure is not that critical as long as you are getting good oil circulation.

:) :grin:

The only part that is lubricated by pressure in a 1931 is the center main bearing. The rest is low pressure, splash and gravity.
The normal oil pressure in a 1937 with a gear pump (and all the mains pressure lubricated) is only 13 pounds at 50 MPH.

Thanks for the info. It sounds like most 1931 Chevy owners stay with the original pump because it is designed to lubricate with low oil pressure. I am going to have to pull that pan off and check that ball valve at the rear main. Is it easily accessable with the pan off in case it is stuck I will need to free it up? I am not sure what I am looking for or how to check its operation.

Would be best to unbolt the rear main bearing cap. There should be thin shims between the cap and block. Do not loose these. Removing the shims is how the bearings are adjusted. Best to consult a shop manual for complete info. The "tighter" the bearing fit less oil will pass thru the bearing, making the return passage do a better job. Once the cap is removed you will have a better understanding of the system.

Thanks for the info. I had better order a pan gasket so that I can put it back togather after checking the valve and the rear bearing clearance. I have been reading the the Chevrolet repair manual on how to adjust the rear bearing and the removal of a shim if needed to make the bearing tighter. Thats whats great about owning one of these old chevy cars. You can work on them without being worried about how to put it back togather. I'm not a mechanic but have done enough over the years to to make iy fun.
Its great to own a old CHEVY.

On my '31 the oil pressure at idle is about 7 but as the engine warms up it seems to drop. After driving for a few minutes, it idles at around 2 or 3. When the engine is warm the oil pressure seems to be around 5 when driving. Is this normal? Also I have an oil pump for a '35. Would that fit the '31?

If you have the factory oil pump then those readings would be normal.

my chevy has the original pump, and I had the oil pan off during last winter and the oil sieve under the pump was blocked and there was incredible much dirt inside the pan because no one of the previous owners did clean pan and pump for decades.
Now everything is clean and I have about 10 pressure after cold start and 4 to 5 when oil gets hot after driving a while.
As the books say, the gauge at dashboard should just show "ok, system works" and the not a true info about real oil pressure.

Mine leaks a bit at rear end too but I was lazy and did not remove the rear bearing cap to check the ball. Have to do it now. Will do it soon because now I use strong detergent oil to clean the egine inside and must surely clean the oil sieve again.
Be careful and remove the steering tie rod between the front wheels to get space to take out the pan without damaging the oil dippers under the crankshaft.

all the best
Stefan

As far as I know it is the factory oil pump. It does relieve my mind to know that it is all right. I just changed the oil and the screen was very dirty. I plan to put some miles on it and then change it again.

There is only one part in your 1931 engine that gets the full pressure shown on the gauge. Its the center crankshaft bearing. The front and rear crankshaft bearings, connecting rod bearings and rocker arms get fed from the low pressure side of the oil distributor valve. That would not require pressure, just a flow of oil. Your pump pressure sounds normal for a 1931 with a vane type pump. Reducing the bearing clearence (if its now too loose) of the center main bearing may possibly raise the pressure by a pound or two.