View Full Version : Big Block Rear Seal

06-10-2000, 07:32 PM
Someone told me that the knurling on the crankshaft where the rear seal rides will not work with the rubber seals. He said you have to use a rope seal or machine the knurling off of the crank. I have never heard of this being a problem. I have never heard of any one removing the knurling and doubt that many people use the rope seal. As you can probably surmise I have a leak on my newly assembled 383 and am second guessing myself. Does anyone have any input on this topic? I am not sure if my leak is from the side seals or the main seal. I just slipped in the rubber seal, slightly offset, dipped the side seals in diesel fuel and slid them home. Comments??????

06-10-2000, 09:47 PM
I just recently freshened up my 71 383 and have the same problem. Used good quality Felpro gaskets, I followed the directions and still ended up with a leak at rear main. It is not to bad but sure makes a mess on concrete and the undercarriage of the car. If anyone has any ideas I'm all ears. Larry

71 Charger 383

06-10-2000, 10:26 PM
Lightly oil the rubber rear main seal. Make sure the lip is towards the inside. Forget soaking the side seals in this or that! Use a gasket maker sealant on the seal housing & the sides of the block that the seal touches, install carefully. Have never had a problem doing it this way.


06-11-2000, 03:57 AM
Belvedere is right on. I just broke in my 440 today. Rear main sealed. I put oil on the seal and only put gasket maker on the sides. My only leak is from a header bolt.

06-11-2000, 11:41 PM
When I put in the rear seal it was in a motor with about 90,000 miles and was previously leaking. I did a valve job on the heads,new oil pump etc. When I replaced the oil seal I put some light grease on the lip of the seal and double checked it was in correctly. I soaked the side seals in mineral spirits and also used gasket maker just to be on the safe side. When I first got the engine running it was not leaking. I did not notice a leak until I added and extra qt. of oil due to having the wrong dipstick installed. It has leaked a little bit ever since. The motor has some blowby but runs great. Even with the leak I only add a qt of oil every 1000 miles or so. It is just embarrasing to park in someones driveway and leave your mark. Help ? Thanks. Larry.

71 Charger 383

06-12-2000, 12:51 AM
I've had the same problems, but the last couple of big blocks I rebuilt, I put a thin coat of blue silicone sealer between the seal halves and the block/seal retainer. Neither has leaked one drop, so it's a coincidence or previous leakage was not between the seal and the crank, but between the seal and the seats.

06-12-2000, 02:16 PM
last summer I replaced the rope rear main seal in a 400. i couldnt find a rope seal so i used a rubber seal with a small dab of silicon on the ends, the crankshaft was knurled. the side seals are suppposed to be soaked in mineral spirits to make them swell and seal, but silicon sealer works too. when I was done it still leaked. so I bought a couple cans of oil stop leak and after a couple months of driving it no longer leaks, and my garage floor doesnt have a pile of floor dry where the car parks.

06-18-2000, 04:06 AM
Thanks for the ideas. I had already tried some stop leak to see if that would help and it seams to be working. Still do not understand what went wrong but...... Thanks again. Larry

71 Charger 383