67 SB: Recommend rear main seal?

[Joe R.]

I have the oil pan off of my 67 327/300 for a cam swap, and I plan to replace the rear main crankshaft seal while I have access to it.

Is there a "best" quality part for this or should I just use a generic replacement? I'd like to use a high quality part so that I don't have to go in there again.

Also, I note that the Paragon catalog lists a "first design, narrow" and a "second design, wide" seal for the small block. I presume that the second design is superior and that both versions fit. Is that correct?

Lastly, I have heard that some people recommend installing the seal slightly rotated (about 1/8 inch), so that the joints between the two seal halfs do not line up exactly with the joints between the bearing cap and the block. Is this a good practice?

Any advice would be most appreciated.

[Joe L.]

Re: 67 SB: Recommend rear main seal?

Joe-----

There were some differences in the design of the small block rear main seals over the years of 1959 through 1985. I've never exactly figured it out, but I'm working on it. The "second design" REPLACED the "first design", so regardless of what year small block one has, it's best to use the "second design". The exception to this rule is if one finds that one has a groove worn in the crankshaft journal sealing surface caused by contact of the seal lip over a period of tens of millions of engine revolutions. In that case, one might want to use the "other" seal design so that the sealing lip is displaced from the original journal location. There are also aftermarket seals available which accomplish the seal lip displacement.

Assuming that there is no grooving problem of the crankshaft journal (which is the usual condition), I would use the current GM seal of GM #10121044. This is a very high quality, fluroelastomer, high vacuum seal. It's the best one out there. Alternatively, you can use the Fel-Pro #2912. These are exactly the same seal (I've even seen the GM #10121044 embossed on some of the Fel-Pro-branded seals; a big "no-no" as far as GM is concerned), although the color may sometimes be different (who cares?).

Displacing the seal ends is a good practice. It also helps prevent the application of the sealer to the ends of the seals (which should not have sealer applied since they are pre-applied with a special adhesive). However, the areas of the the main cap/block adjoining the seal ends MUST have sealer applied. Check your copy of the Chevrolet Service Manual for instructions and diagrams of the area if you are not otherwise familiar with it. Failure to apply sealer to the areas described will virtually guarantee a leak.

[Joe R.]

Re: 67 SB: Recommend rear main seal?

Hi Joe:

Thanks, I will order the GM part. Since I'm placing a GM parts order, does it make sense to also get the GM version of the crank seal on the timing chain cover? If you think that would be a good idea, can you tell me the GM number for the timing cover crank seal? The engine is a 67 327/300.

These seals are such a PIA to replace that I want to use the best ones I can.

[Joe L.]

Re: 67 SB: Recommend rear main seal?

Joe-----

The GM seals are manufactured by the major suppliers. Very often, they are National brand (Federal-Mogul) and the National trademark will be found embossed on the frame of the seal. In any event, ordering it from GM is convenient and a sure way of getting a high quality part (in most cases). The front cover seal is GM #10243247. It currently GM lists for about 16 bucks. Many dealers may have this one in stock. It fits a LOT of applications.

Be VERY careful removing and installing the new cover seal. You don't want to distort the cover in any way when removing the old seal and installing the new seal. Most GM seals will have sealer pre-applied to the outer perimeter of the seal frame and, if so, no additional sealer is necessary.

[Joe R.]

Thanks Joe ! *NM*