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'38 leaky rear main seal ?

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Oil seepage at rear main. I dropped the oil pan and pulled the rear main with the intent on replacing/ or at least inspecting the rear seal for the cause of the leak.

I'm total baffled by what I found. NO oil seal whatsoever! The oil slinger obviously is doing a pretty good job, as oil is not dripping as I would have thought for what I found.


Should there be an oil seal?

Where does the oil seal go? - I was expecting a seperate groove for the seal.

Pic attached


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Rear Main bearing cap.

I'm unfamiliar with vintage engines, so puzzled by some things I've found.

I found shims on the base of the bearing cap.

Can anyone tell me whether it is normal or someone cheating with assembling the engine.

pic attached

additional note: this is a '38 McLaughlin Buick. Engine number matches the body tag, so it's the original engine for the car.

Sparkplug thread is inconsistant with info I seen for US cars, uses 18mm thread.




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that big fat groove is supost to have a rope seal in it.

this is what keeps the oil in. alot of guys try to go back with a neoprem rubber one, with mixed results.

there is a rope gasket on both the top and bottom, the top is a pain to get in and out.

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Shims are standard on these types of bearings. 1935-38 Buick series 40 had no cork oil seal and one oil collecting grove as in your photo. 1935-37 series 50, 60, 80, and 90 had a second grove for a cork seal. 1938 series 60, 80, 90 and all 1939-53 had a braided fabric seal to the rear of the oil collecting grove.

Be shore to put back the same thickness of shims when you put back the bearing cap (if you are not going to adjust the bearings).


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the 1938 series 40 (248 engine) does not have a rope seal in rear main as the 320 did. Oil control is as follows(from 1938 buick shop manual)

1.Cork gaskets(neoprene nowadays)at the vertical joint between bearing cap and crankcase.

2.Agroove in the bearing ahead of the oil collecting groove, drains into crankcase, relieving the oil collecting groove of surplus oil.

3.A ball check in the passage between oil collecting groove and the crankcase, prevents oil from running back when the front of the engine is tilted more than 18 degrees equivalent to a 28% grade.

The rope seal was first used in the 248 engine in 1939. A seal groove was added to the rear of the main cap and block at that time.

Rear main clearance is critical (0007-0022) for the slinger etc to control oil

leakage.Clearance is maintained thru either adding or deleting the shims you

show in your picture. These are factory shims.

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The modern replacement rope seals do not work as well as the old ones (thank you EPA) as the compounds used to make the seals are no longer allowed. The oil they are supposed to stop from leaking out breaks them down after only 2-4 years causing an annoying failure on many engines frown.gif

and the embarassing puddle under the car. The only good side benefit is the automatic rust-proofing of the undercarriage.


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