VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc One Piece Rear Main Oil Seal 1940-1948

I will be posting a number of pictures of how I installed a One Piece modern oil seal in a 1940 Chevrolet 216 engine. Over the years, I had problems with the GM original 2 piece rear main rope seal. I rarely succeeded in successfully installing the original 2 piece rope seals and having these rope seals work very well. I often would leave a good size puddle of oil when I parked my 1940 Chevy. Some people seem skilled in installing the Chevrolet 2 piece rope seals.

This picture shows the block AFTER it has been line bored to accept the modern SKF 37390 seal. The rear main was line bored with all of the main bearing caps installed. Material was ground out in the rear main to accept the oil seal. As you can see, the rear main upper bearing has been placed in the block.

dtm
stay tuned, I will post more pictures.

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This picture shows the block with the cranskshaft installed and the rear main seal installed in the upper block. The diameter of this modern seal is the Outside Diameter of the seal MINUS .006". This is the figure that the seal manufacturer recommends so that the seal will not rotate once the lower rear main bearing cap is torqued down. The metal outside diameter of the new rear main bearing seal is blue. So in order to install this seal, the block needs to be sent to a machine shop. They set up the 4 main bearings in a line boring machine. Then material ( steel ) is removed from the rear main area with the rear main bearing cap bolted in place. A significant amount of steel is removed in this process. The seal is cheap, the machining costs real money.


Note: Ignore the white lithium grease that is on the rear main bearing surface. I didn't install the crankshaft with Lithium grease, I installed the crankshaft and engine using Clevite Bearing Guard.

This picture shows 2 shims. The one on the left side is for use with the original rope seal. The shim on the right side has been cut / trimmed in order to provide clearance for the one piece rear main oil seal. For 1940 Chevrolet 216 cu. in engines, you would use an SKF Seal # 37390. This seal is 4.751" Outside Diameter. It is designed to work on an I.D. of 3.750". I paid about $23 for this SKF seal.

Make sure that you have the machine shop polish the rear flange of the 1940 crankshaft. This provides a good seal surface for the SKF seal.

dtm

This picture shows the 2 shims installed. As stated before, the brass shims are trimmed in order to accept the new rear main seal from SKF.

dtm

The rear flange of a 1940 Chevy crankshaft is 3.812" Outside Diameter. In order to use SKF Seal # 37390, the rear flange on the crankshaft was surface ground down to 3.750" O.D.

The installed SKF seal does not interfere with the flywheel. There is probably .050" clearance between the face of the seal and when the flywheel is bolted to the crankshaft. This photo shows the block still on the engine stand, therefore I cannot show a picture yet with the flywheel and bell housing bolted onto the block.

The SKF seal has been installed with just a hint of Permatex #2 around the blue outside metal diameter of the seal. The SKF seal is truely held in place by the .006" interference fit, as the diameter that was bored out in the block and rear main cap was 4.745" and the SKF seal measures 4.751" O.D.

NOTE: The crankshaft rear flange diameter is different in 1948, so a different SKF seal is used for that application. Cousin Dale can post the SKF number for installation in a 1948 engine. The 1948 block is bored to a different diameter in order to also get a .006" press fit with the 1948 SKF seal but the process is the same.

dtm

The machining would certainly be the expensive part of the process and be a big improvement in the sealing. The only problem I can see (and most of us wont need to worry) is when the main bearings need to be adjusted the clamping on the outside of the seal will be tightened as well and may distort the seal.
Tony

Dave,

Thanks for posting the great photos of the modification of your 1940 216 motor for a one-piece rear seal. Like you, I have had mixed success with the split rope-type rear seal on my 1940 1/2 ton pickup motor and have threatened to do exactly what you have done. However, I resisted because I was not sure how to deal with the matter of adjusting the rear main bearing when and if needed. As mentioned by Tonyw, removing or adding shims to get the proper clearance on the rear main bearing will change the seal cavity bore, either tightening it or loosening it.

I have access to my brother's machine shop, so the cost of machining won't be an issue for me. One thing I would mention to anyone contemplating this modification would be to put a slight chamfer on the outer edge of the seal cavity bore, which would allow easier installation of a replacement seal when installing with the engine in place.

I'll be interested in knowing how this modification has worked out for you, as I may yet do it on my 40 pickup next time I have the engine out.

Mark

In regards to the issue that this newly improved engine MAY need to have the main bearings adjusted in the future, I have no concerns at all about the rear main one piece seal. The SKF manufacturer recommends .006" presss fit at initial installation. When I potentially remove one .002" brass shim in 20,000+ miles, I am only increasing the crush on the SKF by an additional .002".

The last 216 that I built now has over 30,000+ miles and that engine has the original 2 piece rope seal in it. At 25,000 miles I removed one .002" brass shim from each of the 4 main bearings. I just am not concerned about crushing the brand new SKF seal 25,000 miles from now an additional .002".

dtm

Dave,

Thank you so much for posting these photos and the accompanying information. Expense aside, this doesn't look like a job that should be beyond the capabilities of any machinist that I'd be will to trust to the rest of the work to; in other words, if the shop can't accomplish this, they're probably not the right place to take a Chevy Six to in the first place!

Regarding the seal number for the '48 and later engines, would this also be the same part for the 235 engines as well? I'll be starting on a '54 235 soon, and I'm sure there are plenty of people with both dipper and full-pressure 235's that could benefit from this modification.

Thanks!

Dave,

Thanks for your thoroughness on this topic. Many should remember my trials with my rope seal issues. Please keep updating your post. Your work is important to us all and future hobbyist.

Best wishes, Mike

I have rebuild three 1952 216 engines. All three only drips transmission grease. The two pc. seal needs packed in right and then I roll it in with a short pc. of broom handle. Works great.

So, what kind of rope seals were/are you using? The NOS GM asbestos ones and their auto-parts-store contemporaries seem to be no problem when installed correctly, but everyone I know that has used the modern non-asbestos versions has had anywhere from slightly more than normal leakage to more serious leaks, and the occasional downright failure of the material.

Only NOS group # 0.137 part # 839129. But they still need to be put in properly.

The 2 piece rope seal is tricky to fit properly though I havent had much to do with the later non asbestos type.
Tony

Sorry it took me so long to chime in on this. The seal we used in my '48 engine is an SKF 38649.

Dale,

Thanks! So, did the flange require any change in diameter for this seal, or just the normal resurfacing you'd do as part of typical prep work to the crank?

Thanks,