Rear Main Seal

[Jim K.]

I have the engine out of my car to detail and repair oil leaks. I thought it was going to be the rear main seal, but the back of the block is dry; the inside of the bellhousing is somewhat wet, so I'm at a loss. I did notice that the aluminum intake bolts were fairly loose upon disassembly ant the front intake gasket was popped out. That beeing said, while it's all apart I want to change the rear main seal anyway along with all EXCEPT the head gaskets. I can't find a written proceedure and my old Chilton book is missing. Any thoughts or advice? The motor is a 327 of 1967 vintage. Thanks!!!

[Gene M.]

Re: Rear Main Seal

Jim, the back of the block is above the rear main seal so it will not show signs of an oil leak. I would suggest checking the oil pan end seal and along the flange. These are areas that are very good at, when leaking, allow the bell housing area to get wet.

[Roy Braatz]

Re: Rear Main Seal

Drop the pan , drop the oil pump, drop the rear main crank cap, pushing the old rear main seal end up as you turn the crank enough to grab the other seal end with a needle nose and pull it out, then start the new seal in pushing on the end as you again turn the crank, then add the bottom seal in to the crank cap and reinstall.

[Clem Z.]

be careful

the better seal kits come with a little plastic shim that you place in the groove of the seal so when you rotate the seal into the block you do not cut any rubber from the seal. the sharp corner on the block will cut the rubber if you do not use the plastic shim.

[Joe L.]

Re: Rear Main Seal

Jim------

Afew other tips:

1) Use seal GM #10121044 or Fel-Pro #2912. Both are the same.

2) You ABSOLUTELY MUST apply sealer to the block or cap surface which is adjacent to the seal end and avoid applying sealer to the end of the seal (it's factory-treated with a special adhesive). A diagram of the exact area to apply the sealer can be found in any Chevrolet or Corvette factory service manual, as well as many other references. This MUST be done or the engine will leak, for sure.

[Doug Flaten]

Re: Rear Main Seal

Could your leak possibly be from the front of the Transmission? I've had both the trans and the engine seals give up on different occasions.

[Paul L.]

Re: Rear Main Seal

Joe makes an excellent point re the sealant procedure. Here are the GM instructions in that regard.

[Patrick H.]

Re: Rear Main Seal

Joe,

Of note, the GM and Fel-Pro seals are different color. I purchased both last year when working on my motor, and found that out. Otherwise they are likely identical.

Patrick

[Joe L.]

Re: Rear Main Seal

Patrick-----

That's a change then; they used to be the same color. In fact, I had one out of a Fel-Pro package that had the GM part number embossed on it; that's how I knew, for sure, that they were the same. That one must have been an "error", though. GM doesn't allow their part numbers to be placed on items sold in the aftermarket. Maybe Fel-Pro ran short of the "generic" ones and packaged some with the GM part number. Perhaps, also, they now use different colors to distinguish the Fel-Pro versions from the GM versions to keep GM happy.

[Patrick H.]

Re: Rear Main Seal

Joe,

Who knows. They otherwise appeared to be essentially the same. I first used one, and then when I inserted it "too far" and it went out the other side, it got a tiny tear when I tried to re-insert it. Not wanting that, I pulled it out and used the second one.

I don't recall which actually is in my engine right now, but it works. No substantial leaks anymore, but it was difficult to tell the exact source of the leak anyway.

[Jim K.]

Re: Rear Main Seal

Thanks to all, you guys are the best!!!
Doug: Great tip, I am replacing all the trans seals as well.
Paul: That photo was exactly what I needed, I didn't know what they ment by chamfer... thanks!
Joe, Clem, Patrick, Roy & Gene you info was a great help too, the whole thing seems a lot less intimidating now.

One more related question I plan on cleaning all gasket surfaces (not the crank) and applying a small amount of blue RTV to everything (Block, oil pan, timing cover, etc) with a small dab on the four corners wnere the pan gaskets ends are; then partially torque down the pan, let the RTV set and fully torque down after several hours. Is this overkill, recommended, or a bad idea????

[Patrick H.]

Re: Rear Main Seal

Jim,

Use the one-piece oil pan gasket from Fel-Pro. It's blue, so you will have to paint the edges of it orange before you install it (I did) but it is a FAR better gasket than the usual 4-piece ones. You will still need a touch of sealant at the front and rear corners. In addition, be SURE that you have straightened and flattened the edges of your oil pan, and the bolt holes aren't sticking out towards the pan from having been overtightened previously. Once you do this, your oil leaks will be no more.

Patrick

[Jim K.]

Re: Rear Main Seal

I never knew a one piece existed, I'll try to get one. Are they a shelf item, oe special order?

[Jim T.]

Re: Rear Main Seal

Jim there are now available one piece pan gaskets. Not sure if one is made for your 61. Of course it would not be NCRS correct, but don't know how many points would be lost.

[Joe L.]

Re: Rear Main Seal

Jim-----

Fel-Pro OS-34509-T. Available from any Fel-Pro gasket retailer.