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You can use this method to install either a new Felt seal or the neophrene one shown below
After removing the crankshaft hub and timing cover, The existing felt seal has a retainer with 4 cap head, self threading screws.
Carefully remove the retainer screws with a firm grip, so as not to damage the threads. you might even want to note which hole each screw came from, if you're picky
Remove the old felt seal and clean up the recess.
The new neophrene seal is a Victor 62402 or NAPA 19887 and 'ALMOST' fits exactly.
The NCSDC website has a similar installation, but with a National seal #472924 and a National #99200 Speedi-sleeve. Both type oil seals cost around $10.00 and both types of Speedi-sleeves cost around $30.00 ( yes, thirty)
If you are to use the original retainer screws, the edges of the new seal must be peened over to reduce the edge height. The original screws are not long enough to bite into the timing cover using the seal as it comes in the box. You can opt to get 4 10 x 32 machine screws and a bunch of small washers to span the distance between the retainer and the cover, but a bit of careful massaging will work without distorting the seal. Light taps on a firm surface working around the edge.
This shows the edge height after peening the seal compared to the original seal as it was removed from the cover. The original seal has expanded a bit with the pressure of the retainer removed and is about as wide as the neophrene before peening.
Place the seal in the recess with the open end toward the engine. The added feature of this new seal is that it doesn't EXACTLY fit in the opening but is very close. So what has to be done, is for you to drain one of your favorite beers and cut some small strips from the can. The strips should be 3/16 wide an d 1.5 inches long. The thickness of the beer can aluminum exactly makes up the difference if 4 strips are equally spaced around the perimeter between the seal and the timing cover recess.
You can see the edge of one of the strips on the left side of the seal. You will have to coax the last one or two in place because they make the seal very snug in the recess.
When replacing the retainer, use Lok-Tite on the small screws, then you can test fit the hub. Don't forget to oil the seal before you do this and once more when you refit everything to the engine. You can also add a sleeve (National Speedi Sleeve 99199) to the outside diameter of the hub to prevent the oil return spiral from damaging the seal
Important Note: When installing the timing over, leave the bolts loose, until the hub is pressed back on the crankshaft. This will center the seal on the hub and prevent distorting it. Once the hub is snug, tighten the timing cover bolts.