VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 rear main oil seal leak (rebuilt 216)

It took a while (beggars must be patient)but my buddy (with a lift) and I replaced the rear seal today. He did most of it. Hopefully, it is my first and last such ordeal! At least it wasn't missing the alignment pins.

As some guessed, the newer type seal had been used (it leaked a quart in 35 - 40 miles!). I got the rope seal and a pan set from the Filling Station. I also ordered a "Sneaky Pete" on line.

'Had a terrible time with the upper seal. We loosened all the main bearings and slid the trans back to clear the front bearing cover and its bolts to gain a bit of clearance for the seal (as was mentioned here). Each time we got the upper seal started, the "sneaky" would pull out. Pure, repeated frustration for hours! My buddy had done 6 or more of these (on his back without a lift) and had never had such a problem. He did have 2 more pieces of "rope" - same size and material. We about wore 2 pieces out with no luck. Each time the "sneaky pulled out, it damaged the end of the "rope". Amazingly, on the first try with the THIRD piece, the seal went in like one would expect it to do! Finally!

Hopefully, the leak is fixed. I drove the '41 about 15 miles home and 4 hours later, no sign of a leak. I guess I'll know after putting some miles on it.

I thank each and every one who responded to my problem. Each of you was helpful at a time when I needed help and advice. I'm sincerly grateful to one and all.

I really think that the rope seal is the best fit for a 216, 235, 261 Chevy six.

Happy it wasn't the pins, but it can happen. You talk about something fun to install without removing the flywheel.....wow!

'Glad I wasn't missing the pins!! It was difficult enough as it was. 'Turned into an all-day job. If the first seal had gone in like the third one, we'd have been done by noon.

Fifteen miles isn't much of a test. 'Sure hope she stays dry.

Well, when I park, she's leaving a spot of oil about the size of a nickel or a quarter at the most. Of course, it is leaking going down the road as well ('haven't put but about 50 miles on it). I'm gonna watch the stick closely. If the oil level doesn't drop significantly, I'll just live with it. If it becomes significant (hope not), I'll do it all again! Perish the thought!!!

Thanks again.

Thanks for updating us on your project. A lot of us have suffered through replacing the rear seal only to have it continue to leak and even leak worse. Any suggestions are always appreciated. I am right now having an engine professionally rebuilt because I gave up on trying to solve my rear seal leak and the engine had poor compression. My biggest concern is that the rebuilt engine will also leak!!! Good luck, Mike

P.S. Of course a leaking rear seal will eventually mean a contaminated clutch disk which equals clutch chatter, etc., which I have also dealt a lot with!!!

When replacing the rear main, the clearance on all the mains should be checked and adjusted if necessary. That is important to prevent large leaks from the seal. I use a piece of shim stock laid across the lower bearing half determine the existing clearance.

Another quick way to check the clearance is to use a cigarette paper(used for rolling your own)doubled over,and placed between the crank journal & bearing under test.This will give you around the .001" to .0015" clearance mark.If,with the folded paper between the bearing & journal,the crank can't be turned,then you'll have about the right clearance.A bit a a bush method of checking bearing to journal clearances,but it always works.This method is even suggested in the "Dykes Automotive Encyclopaedia".

'Guess we should have checked the main bearing clearance but the engine only has about 400 miles on a complete, EXPENSIVE rebuild (PO had it done)-new mains, insert rod bearings etc. So, we really didn't worry about the main journal.

We had trouble cutting the upper seal after installing it (even with 2 new razor knifes). I think that is the cause of the leak. However, if it doesn't get worse, I'll just live with it. (I have ordered another seal and pan set "just in case.)

Rope seals seem very primative to me until I consider how long Olds used 'em in millions of 307 V/8 engines (on two of which I put 175K with no evidence of a leak.

The orig leak was due to a modern neoprene seal installed during the rebuild. It may have fit the shaft but it did not fill the "groove". So, oil could simply flow around the seal.

I will continue to watch it and report on the leak. (Ain't old cars fun!)

If you did a large scientific poll, I think you would find that the majority would leave a drop here and there on these old 216s.

Just because somebody spent lots of money to have an engine rebuilt doesn't guarantee that the clearance for the bearings is done right. I've seen many "experts" shim the bearings to the loose side only to end up with main seal leaks.

On an older highway or street surface if you look for the dark spots it will help to identify upcoming bumps (spot is immediately before the bump). Those bumps help concentrate oil drips on vehicles using the road. Since the vast majority of those vehicles are less than 10 years old it is evidence that they leak too.

All, every cotton pickin' one, allus, total entirety, utmost possible, each, wholly, to any extent (pick one) old Chevrolet 207, 216, 235 and 261, etc, seep oil at the rear main. Granted some more than others; owing to age of the engine and condition of the seals. That's why the hole is in the flywheel cover. (Well, duh.)

Take a deep breath and accept this fact. One may come close to eleminating the seepage but never completely. Let's face it, if you drive the vehicle, the seep will always be there. From day one. Will too.

Happiness is accepting the things you can't do nothing about. I do not drive my old Chevrolets up a persons nice white, spot-free, concrete driveway and park thereon. It will drip before you can open the trunk and get the pan or piece of cardboard out and slide it under the engine, no matter how agile and swift you are. I park in the street.

My two cents worth.
Charlie

BTW: Chipper, good point, but it seems to me that the spots on the highway are right at or just aft the "bump" not before.

Charlie,
You got me on that one. I was thinking and meant to write the dark spot is immediately after the bump or bump immediately before the dark spot but got befuddled or worse. Thanks for the correction.

I gotta put a piece 'o cardboard under my car and see if'n I get any drips...I saw a drop hanging off the back of the transmission a while back...Maybe it was blown there while driving and I've seen a drip hanging from the hole in the flywheel cover...But I don't see any spots on the pavement...There are some seeps on the engine and black drips from the filler tube but for how old this 216 is, it must be one of my blessings...Better quit talking about it now, before I jinx the whole deal...

I think this problems runs in the same chain of thoughts that Mr. Henry Ford used (to play every angle to benefit your profits)
"Well lets see now, we have a problem stopping these cars from leaking oil. So instead of hiring new engineers to solve the problem, we will use the money that we would have paid those new engineers and buy stock in all the major oil companies, or buy the oil company's themselves"
Now the more oil our cars leak the more money we make..Simple.
Mr. Ford was a genius on stuff like this....ED

Oh, so that's why they leak so much...! You think maybe the gasket/seal companies might be in on this, too...? Hmmmm

All points well taken. I hope the rebuild was at least fairly well done. The PO paid FAR too much for it. I hope the fact that they left the vac line (plugged) off the vac advance and omitted the clutch pedal return spring isn't indication of the quality of the engine rebuild. Time will tell. I'm still trying to see whether I've got the '41 or its got me!

Yes, I'm aware of and resigned to Chevy 6's leak oil (at several places). Frankly, if it doesn't leak more than a quart in 1000 miles, I'm gonna ignore the leaks and just watch the oil level closely. Too soon to know. I am very glad it isn't leaking at the rate of a quart in 35 miles! And, it doesn't have to be perfect to be fun.

I've been messing with ol' rides a long time now and you can see the evidence of it by the dark stains on my garage floor. So, I ain't surprised. They all leak - some of 'em at both ends.

My first running car was a '41 Chevy MD 2 door (1953) followed by a '47 SD club coupe (1954/5). Although driven unmercifully, neither used/leaked enough oil to bother. (The '47 used a quart in 2000 miles.) 'Always had a soft spot for '41s but it has been 58 years between owning one.

Thanks a lot, men for your comments, advice and help. There's a bunch of nice folks on here.

Gaither:

I've got a 48 Fleetmaster with her original engine. THe PO told me the engine had been recently rebuilt when I bought the car 3 Summer's ago. The rear main seal leaks on mine too. I found that putting Castrol 10W-30 High Mileage oil in her seems to minimize the size of the puddle I get.

Regards:
Oldengineer

I also have had good luck with the high mileage oil. Maybe its got some swelling agent in there but I notice my Fleetline dribbles less out the back. Maybe its the psychological effect of paying more for the high mileage oil that makes me "think" its dripping less, but its still worth it. Wally World even has a cheaper house brand high mileage oil that isn't too bad.

The high-mileage oil is a good idea. I've used it on late model engines with leaky valve guide seals. Darned stuff works!

High milage oils and seal swellers will do nothing for a rope type seal.They could swell up a neoprene seal but it would take a few thousand miles. A 1941 Chevrolet had no neoprene seals. If it has a later timing cover seal it would be neoprene. The original was leather.
You can purvhase seal swellers as an oil additive.
All good oils have some seal sweller built in. It is there more or less just to keep the seals soft.