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Author Topic: Potential Rear Main Oil leak.  (Read 7225 times)
Challenger340
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« on: November 03, 2007, 12:00:31 PM »

Here's something for you guys to watch out for if you assemble your own engines.

I wasn't gonna post this, dunno if there is a need or not.

Anyways, I just can't be small minded enough to believe, that something I know, should be kept to myself, just because I'm "in the business", or,
that I may have "proprietary" reasons with certain individuals on this Site, NOT to dosclose for ALL to benefit.
I just ain't built that way !

That just wouldn't be in the what I'll call "spirit", of a bunch of Old Mopar lovers plunk'in away on a keyboard on this Site.
We should be here to SHARE, and HELP each other !

That has to be the bottom line for my presence here as well.

Anyways, put it under "TECH", or wherever it "fits".

We'll leave the specifics of block castings, date of manu, casting plant info, out of this discussion. Suffice to say, that could be a NOVEL unto itself, and I'm always too long-winded anyways.

Let's just say checking "this", should be on everyones list during assembly of all BB Mopars.

We've seen it on dozens of BB Mopars with REAR MAIN LEAKS, after assembling Hundreds.

There exists a manufacturing defect in many BB castings, in that the groove that holds the Rear Main Seal in the Block, is "offset", or rather, NOT CONCENTRIC with the Crankshaft Centerline(mains).

It can be very subtle, or obvious, and a standout to the eye at first glance when you been doing them awhile.

Obviously, if the Rear Main Seal half is installed in these "off-center" blocks, depending upon the degree of the defect in the particular block, the Lip seal compression on one side, (typically the Passenger side of the Block from factory), is insufficient, resulting in a delayed Oil Leak, until the Oil temp increases sufficiently to warm and deflect the neoprene seal.

The "FIX", involves firstly, looking for & recognizing this defect before you get a puddle on the floor. That is why during assembly it must be checked. Put in on your "TO DO" list !

We've forgot about it, and had "oily Shoe-sees" a few times over the decades !

Install The rear main lip seal half in the block "flush" with the cap parting line.
Install the Crank.
If your Lip Seal compression on one side, is less than the other under close inspection with a light, with the Crank in the block, you have a potential for a leaky main.
Gently, using a small screwdriver, GENTLY, insert it behind the offending side of poor compression, and "eyeball" the amount required to equal Lip compression "side to side".
DO NOT damage the back of the seal with the screwdriver. It doesn't take much.
Record the amount required to move the lip seal into equal compression.

Now dis-assemble.

Re-assemble this time, with the Block side Rear Seal lip half protruding approx. 1/4" above the parting line on the offending side.
Reverse the same Seal offset installation in the Retainer.
Now use the Retainer when installing, to CAPTURE and DRAG the offending poor contact side over into proper seal lip compression, the same amount as you recorded earlier, as you Tighten & Torque the Seal Retianer into place.
Silicon up the sides of the Seal Retainer to the Block, deleting the paper inserts. (The paper side inserts probably won't go in anyways due to the Retainer offset installation)

Sometimes it's the SIMPLE things that cause alot of headaches, later, after assembly.

Just something to "watch out for".

I'll check with Brandon at 440source, I dunno if he's run into this or not ?

Might be a good "piece of paper" to include in his kits with the Cranks he sells.
Many Oil leaks probably aren't his Cranks fault.
But it might lessen some Customer perception headaches for him.

Thats it, Thats all,

I said my peace,

Bob out.



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« Reply #1 on: November 03, 2007, 02:27:24 PM »

bob,  i seen the other thread and was kinda dissapointed you took it to pms,   so thank you for your time typing this up and posting.  its  always nice to learn!
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firefighter3931
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« Reply #2 on: November 03, 2007, 03:43:52 PM »

Bob, thanks for posting this valuable information !  2thumbs

When our paths cross some day the first 10 beers are on me !  icon_smile_big  cheers


Ron
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max
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« Reply #3 on: November 07, 2007, 08:53:09 AM »

Bob as usally thanks for that helpfull information. i remember when there was a time or two i had to really look at the lip of those mains to make sure i even had them installed the right way. lol

those rear main seals are the reasons i always start the engines up on the garage floor, just to be sure they didn't leak coarse alot of folks either don't take the time or know how to do that.

one thing i have read over the years but haven't tried, is to off set the halfs of the seal. meaning when you put the half in the block push it down where one side is roughly a 1/8" down in the block and the other side will be a 1/8" above the block on the other side.

coarse the samething is done to the cap to match that of the seal in the block that way the parting lines of the seal isn't parting where the cap meets the block.

have you ever done this and have you found it to be of any benefit?
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Challenger340
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« Reply #4 on: November 08, 2007, 06:28:33 PM »

Bob as usally thanks for that helpfull information. i remember when there was a time or two i had to really look at the lip of those mains to make sure i even had them installed the right way. lol

those rear main seals are the reasons i always start the engines up on the garage floor, just to be sure they didn't leak coarse alot of folks either don't take the time or know how to do that.

one thing i have read over the years but haven't tried, is to off set the halfs of the seal. meaning when you put the half in the block push it down where one side is roughly a 1/8" down in the block and the other side will be a 1/8" above the block on the other side.

coarse the samething is done to the cap to match that of the seal in the block that way the parting lines of the seal isn't parting where the cap meets the block.

have you ever done this and have you found it to be of any benefit?

Yep, thats exactly what I'm talking about MAX.

If you re-read my post, I was trying to get at that.
You should only install the seal "flush" for the checking portion of seal lip "contact", prior to actual installation.
You then install the seal halfs offset from the parting line, but use the reatainer to "capture & Drag" the seal into contact on the bad side, as you're torquing it up.

I was too long winded as usual !
But if you read it all the way through, you'll get the gist !

Only you said it way better !
Thanks Max,

Bob out.
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max
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« Reply #5 on: November 09, 2007, 02:01:38 PM »

Bob, sorry about that.

it wasn't you, i let my fingers type before my brain kicked in slap
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