VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 1937 216 rear main oil leak---Help

Hey Guys.. I had my original 216 engine professionally rebuilt, now the rear main bearing leaks while driving and when you turn it off leaks a spot about the size of a silver dollar, also is slinging oil into the clutch area. Since this is the original engine it does not have a rear main seal, there is a grove in the lower bearing half that directs oil back into the hole in the cap for drain back and my shop modified the front lower section of the bearing by cutting two .30 groves at 5 and 7 o'clock for drain back into pan as we had read about on the net. Does anyone have any ideas or cures for this issue? Thanks

The is a drain back grove in the cap. Not common to plug-up on a 1937.
Excessive bearing clearence can cause some leakage.
What I did on my '39 years ago was cut a small grove in the lower bearing from the center grove in the insert to the front of the engine. This lessens the oil pressure to the rear half of the bearing,
I found this tip in the book "Cast Iron Wonder" It said to cut the grove with two hack saw blades held side by side about .020 " deep Worked well and drove the car many thousands of miles on the interstate.

The drain back in the cap is open and I cut the bearing shell at 5 & 7 o'clock, also the main bearing gaps are below .002. I had been running straight 30 weight oil and have since read to use 10-30 or 10-40 Rotella, thanks for your reply.

I would recpmmend 10W-30 oil with no additives necessary.

You may want to check this link out http://chevy.oldcarmanualproject.com/shop/1938/38csm136.html which is to the 1938 Chevy shop manual on Old Online Chevy Manuals website. As with all 1929-39 Chevrolets, there is a clearance that has to be maintained between the back of the crank oil slinger and the ledge of the block. The manuals say .002-.032 inches. This clearance is controlled by the thrust bearing front face. If something is wrong with your slinger or the center main bearing is not correct and as noted before the oil drain passage is partially plugged in the rear main bearing cap, you will have oil leakage out the back of the engine. I am not completely sure of this but if the camshaft plug in the block isn't seated properly, oil could leak out of into in the flywheel housing also.