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Half a Rear Main Seal?


hkestes41

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I will be headed from Texas to the HAMB Drags in Missouri in a couple of weeks. My rear main leak has gotten to the point where I think I should change it before heading out on an 800 mile round trip.

Reading the Service Manual it says the following concerning the seal.

"UPPER OIL SEAL RETAINER - If inspection indicates that the upper oil seal retainer must be replaced, remove the flywheel. Remove the upper retainer cap screws and remove the upper retainer."

This brings a couple of questions to mind.

1) What exactly would I be looking for when inspecting the upper seal?

2) Could replacing the lower and leaving the upper actually be acceptable?

3) Do the lower seals wear much faster than the uppers?

4) Would I need to remove the bellhousing to replace the upper seal?

Before reading the manual I would not have even considered replacing just half the seal. I would just automatically done both upper and lower, now I'm not so sure.

Also if the bellhousing must come off the block it will require pulling the engine to get to as a previous owner welded the removable floor into place and there is not enough room to get to all the bolts between the bellhousing and block. That is why after reading the manual I would consider replacing just the lower.

And I thought the manual was supposed to clear things up.

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There is not only the upper and lower halves behind the crank flange but also a rubber seal in the rear main bearing cap (all part of the 'rear main oil seal'). Hard to tell which part is leaking. A PITA no matter how you tackle the replacement.

Phil

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PITA..didnttake long to figure that one out.!

i have to consider replacing the seals also. there is an upper and lower..the 3 bolts holding the lower half of the seal are in the bearing cap . take that out and the seal (a thin metal piece with a rubber squeegee type edge) is easily replaced. the upper one.well you cant get to the bolts (caps crews) so you have to take the whole damn thing apart flywheel/clutch/etc because the cap screws are snuggled in behind the flywheel and they wont back out unless the flywheel is removed..

I have a 'beater' engine on the garage floor that i use to rip into these problem jobs. and yes there are 2 of the rope pieces that squish in the bearing cap upper and lower too.

as to whether the lower wears out faster and might possibly be the leaky culprit...i can see where that theory came from! looks like a heck of a job..

bill.......dont know much just observation.

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i thought i saw an upper and lower rope seal located in the bearing cap housing. also there is a very thin 2 part metal plate with a rubber wiper on it. this is outside the housing and is fastened with 3 bolts (cap screws), called upper and lower oil seal 'retainer'. this lower oil seal (retainer ) is accessible when the bearing cap is removed. the upper is impossible to get at with motor installed unless you take everything off down to and inc. the flywheel to get at the 3 cap screws (bolts).

consequently you can see why there is/has been talk for years by owners and mechanics about only replacing the lower half. one takes 2 hours..the other probably 12. !!!!! hoping that the lower one is the leaky culprit..50/50

....i hope it is a clear description of the procedure. not a MECHANIC JUST LOOKIN' AT IT !! and the manual.

bill

Edited by claybill
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There are two styles the old rope style which you can change the top part of in the car, once the flywheel is off, and the newer 1950 or so 2 piece insert with neoprene. I've had both in my 46. Both leaked. Had the crank removed and spraywelded and turned, the rust on the crak tore up the seal, then the ew oe leaked after the machining. My rebuilt 56 motor has the more modern one and it leaks also. Not badly but still leaks nontheless.

Guess its a family trait. So why not try to get the bottom on and see what happens. won;t stop all of it but if it stops some if it your ahead of the game a bit.

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There are two types of neopene seal - early and late. My 1948 has the type mentioned in this thread with three cap screws holding it in place. And as mentioned, the only way to get the top half out is to pull the flywheel and all that it involves. Around 1951 a newer type seal was used that is serviceable from the bottom, if you loosen the crank. Unfortunately these two do not interchange as the blocks are machined differently.

There were about three changes to engine blocks at this same time. When the rear main seal was redesigned, they also did away with a positive oiler spout and orifice to the front timing chain, and replaced that neat feature with a disc slinger on the crank, behind the lower timing chain gear. This positive oiler was a great ldea, plugged into the front of the main oil galley and did a good job - until the engine got so sludged up that the thing plugged up. That's how I found mine when I took things apart.

The third change I am aware of on the later blocks was a redesigned rod cap and fastener design. Earlier engines used a very thin lock washer under each rod nut. This all fit inside a recessed spot on each rod cap. Later designs used a locking nut with no recess.

When I rebuilt my B1B engine, I had a spare engine apart at the same time. One was early and one was later. I used one rod from the later engine in my early design engine because I had one loose wrist pin bushing. Rather than replace this bushing, I just swapped rods. Amazingly, both the early and late rods carried the identical part number.

There may well be some other changes that also were made to these engines that are beyond my knowledge. These were the three items I found while comparing parts between the two. I also confess to putting in a new lower main seal and leaving the top half in place, rather than pulling the whole drive train out just to get to three screws. Hasn't leaked yet. :D

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