Mystery Rear Main Seal leak

S10Vette

Member
When I rebuilt my 1951 8N, I went to a single piece lip seal in the front, and it is sealing perfectly.

For the rear seal I just could not seem to get the standard rear rope seal to fit in the groove flat enough to avoid completely binding the crankshaft. I even tried two different brands with no success. Yes, I tried rolling it with a large socket and lots of pressure.

So, failing that I installed a graphite impregnated seal designed for a flathead V8. That seemed to work better, but now likely not enough contact force, because it leaks.

So, the MYSTERY is that it does not leak at all with the engine running at a fast idle even for 20 minutes or so, but as soon as I shut off the engine, it drips a puddle about 5 inches in diameter fairly quickly, then settles into about 1 drip every 30 minutes.

It is definitely engine oil not trans/hydraulic, as I added dye to the engine oil and it glows bright under UV.

I am going to live with it for now, but still very curious about why it does not drip while running. Any ideas and has anybody seen that before?
 
While the engine is running the flywheel and clutch assembly are moving enough air to fling the oil around inside the clutch housing. When you shut the engine off the air flow stops and the oil settles to the bottom and drips out the weep hole.

Mark
 
(quoted from post at 16:12:25 12/15/16) While the engine is running the flywheel and clutch assembly are moving enough air to fling the oil around inside the clutch housing. When you shut the engine off the air flow stops and the oil settles to the bottom and drips out the weep hole.

Mark

Pretty good theory I had not thought about the air flow, just thinking gravity and centrifugal "fling". One odd thing is that the outer edge of the flywheel and ring gear teeth are completely clean and dry so it does not wrap around the edge at all. A little concerned the oil that gets flung to the top of the bellhousing could drip onto the clutch, but [u:d5961c0f4d]so far [/u:d5961c0f4d]that is not happening.
 
I have rebuilt 3 N engines and (knock on wood) have no rear main seal leakage. I followed the tutorial of John Korschot. It is
posted under the how-tos on the other board.
 
(quoted from post at 19:42:08 12/15/16) I have rebuilt 3 N engines and (knock on wood) have no rear main seal leakage. I followed the tutorial of John Korschot. It is
posted under the how-tos on the other board.

Just read through his procedure, and noted a couple of things. He says either dry or oil soaked will work, and has done both successfully (no need to debate that I am sure he is not just making that up). What I like about dry is that the ends can be sealed with RTV.[b:d7e5ac6af8] Which did you do ?[/b:d7e5ac6af8] He also says that when done properly the crank should rotate with not much force. That's where I had a problem as my original installation practically locked the crank from rotating, which is why I gave up on the oem type rope seals. After installation could you rotate the crank by hand?
 

The more times you replace the rear seal the better you will get at it just like John Korschot learned...

Many dumb arses provide info on N boards few have BTDT and learned from there mistakes... Rear seals replacement advice and pan gasket fit issues are at the top of the list of advice from folks that don't know there arse from a hole in the ground...
 
(quoted from post at 20:05:13 12/15/16)
The more times you replace the rear seal the better you will get at it just like John Korschot learned...

...

I was all set to try again at this, but now the leak has almost completely stopped on its own. Since the graphite loaded seals are not supposed to be soaked in oil prior to installation, only thing I can think is that they eventually absorbed oil and expanded enough to seal. No way am I endorsing the graphite impregnated seals, but in this case it seems to be OK for now). Another guy here recommended going from 5w-30 synthetic to 30W conventional. I used the lighter grade (along with a Zinc supplement) because all my clearances are at the tight end of the range, but that could very well be part of the problem.
 
I have done more than my fair share of those seals and in differed applications... You can look at this link and see what I had to say about graphite seals back in 2006. There are more about this use graphite in the search box and Hobo,NC in the author box.





http://forums.yesterdaystractors.com/viewtopic.php?t=1181740&highlight=graphite

I could tell the V8 seal was a big gamble so did not go there. I have nuttin again graphite and would prefer to use them I will if I ever find one I am comfortable with.

Now that I have ragged you arse on the 6V thang " its a band-aid that is not TRUE" its a excuse that only satisfies those that make it up. Lets get that leak fixed lets do it one time and move on with life...

A old Britt staying..

Keep calm and carry on there are gonna be some bumps in the road...
 

Thanks for that link, I wish I had seen that sooner. Good Grief on the 90 ft-lbs though. My motor takes 20 ft-lbs to breakaway and less than 15 ft-lbs to keep it rotating (without spark plugs, but clutch engaged in neutral). That means new rope seals are 75% of the rotational "friction". Now that is certainly a time you would want 12V jumper to the starter motor !

Now that I see the practically "locked up" crank is sort of normal for new rope seals, I think I was probably OK with the first assembly. I just thought that "this can't be right".

No worries on the 12V lecture, I should have said most emphatically IMHO which it still is. I have not looked at that thread again and best to let it die as I obviously ruffled some feathers on that one !
 

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