360 Rear Main Seal Leak Question --- AGAIN

Posted By: Mapandjlp

360 Rear Main Seal Leak Question --- AGAIN - 04/06/13 01:33 PM

I've had what appears to be a slight drip from the rear main on my 360 since assembly last winter. After about 4,000 miles last year, it hadn't changed. A few drips on the floor. This year, I switched from HR2 (10-30) oil to HR1 (15-50) oil to get the pressure up a bit. It was carrying about 20 to 25 psi at idle. Now the pressure is better, about 35 psi at idle, 70 at high RPM, but the leak has increased tremendously. After the inaugural trip for the spring last weekend, I went out of town for the week only to come home to a CD sized puddle under the car ('70 Challenger).

Before I pull this thing and replace the rear seal, can you guys confirm that this sounds right?

For what it's worth, I can't find any leaks up high; intake, sending unit, valve covers, etc.

Posted By: JohnRR

Re: 360 Rear Main Seal Leak Question --- AGAIN - 04/06/13 01:44 PM

The rear main seal is not a seal under pressure other than blow by gasses, increasing your oil pressure should not have really made the leak worse ?

What I'd be a little concerned with is your bandaid approach at a potential low oil pressure problem ? ?

Posted By: MoparforLife

Re: 360 Rear Main Seal Leak Question --- AGAIN - 04/06/13 01:48 PM

Are you sure that it is the rear main seal??? It could also be the rear pan seal that if not installed carefully have a tendency to leak. Must make sure that the grove in the camp is very clan and dry and that the indentations in the cap/block are clean so that the end tabs of the rubber fit up tight in these. I have had the best luck putting this seal in dry and using just a tad of silicone in the coners where the pan gasket meets it.

Posted By: Mapandjlp

Re: 360 Rear Main Seal Leak Question --- AGAIN - 04/06/13 01:52 PM

Well, I hadn't thought of it as a band aid approach to a low oil pressure problem. For some folks, 20 to 25 psi at idle and 55 to 60 psi at speed are fine. But I wanted to try and bring it up a little so I tried a thicker oil.

Back on topic, so when the pump is pumping oil to the main bearings, it's not applying any pressure to the seal lip? I was under the impression that that pressure is what helps to drive the seal lip into the crank sealing surface aiding in the sealing characteristics of the rubber seal lip.

Posted By: Mapandjlp

Re: 360 Rear Main Seal Leak Question --- AGAIN - 04/06/13 01:55 PM

Quote:

Are you sure that it is the rear main seal??? It could also be the rear pan seal that if not installed carefully have a tendency to leak. Must make sure that the grove in the camp is very clan and dry and that the indentations in the cap/block are clean so that the end tabs of the rubber fit up tight in these. I have had the best luck putting this seal in dry and using just a tad of silicone in the coners where the pan gasket meets it.

I've read now, as well, that some folks put sealer between the rear main cap and the block. I did not. Could it be bleeding past that?

Posted By: GODSCOUNTRY340

Re: 360 Rear Main Seal Leak Question --- AGAIN - 04/06/13 04:21 PM

Oil pressure doesn't keep the seal tight to the crankshaft, the seal has some crush built into it and when the cap is torqued down, that compression pressure keeps the seal tight to the crank. I always put sealer between the cap and block, if it's not there it could cause your leak. A seal installed backwards would also make it leak, or any damage to the sealing area of the crank. I also put a little drop of sealer on each end of the seal where they butt together, just to be sure. One other possibility is that the rear main bearing has a lot of clearance causing excess oil to flood the seal forcing it to leak. When you have it torn down check the bearing clearance with plasti-gauge, if it's more than .003" it may be your problem.

Posted By: Mapandjlp

Re: 360 Rear Main Seal Leak Question --- AGAIN - 04/06/13 04:26 PM

Quote:

Oil pressure doesn't keep the seal tight to the crankshaft, the seal has some crush built into it and when the cap is torqued down, that compression pressure keeps the seal tight to the crank. I always put sealer between the cap and block, if it's not there it could cause your leak. A seal installed backwards would also make it leak, or any damage to the sealing area of the crank. I also put a little drop of sealer on each end of the seal where they butt together, just to be sure. One other possibility is that the rear main bearing has a lot of clearance causing excess oil to flood the seal forcing it to leak. When you have it torn down check the bearing clearance with plasti-gauge, if it's more than .003" it may be your problem.

Thanks for the feedback! All good stuff. I built the motor myself and checked the clearances on assembly. The rear main was at .002. Of course, that doesn't mean that it still is! I'll double check when I have it apart.

Posted By: MoparforLife

Re: 360 Rear Main Seal Leak Question --- AGAIN - 04/06/13 04:28 PM

Quote:

Quote:

Are you sure that it is the rear main seal??? It could also be the rear pan seal that if not installed carefully have a tendency to leak. Must make sure that the grove in the camp is very clan and dry and that the indentations in the cap/block are clean so that the end tabs of the rubber fit up tight in these. I have had the best luck putting this seal in dry and using just a tad of silicone in the coners where the pan gasket meets it.

I've read now, as well, that some folks put sealer between the rear main cap and the block. I did not. Could it be bleeding past that?

We have had batter sealing using no sealer between the rubber end gasket and the pan. Making sure that all surfaces are clean and dry seems to give a better sealing surface. along with the recesses that the end tabs fit into. If they are not clean the gasket cannot fit down in the cap groove tight. Like I said the only sealer we use is a small dab of silicone in the corners where the pan gasket meets the cap rubber. so far haven't had a leakage problem on 360's

Posted By: GODSCOUNTRY340

Re: 360 Rear Main Seal Leak Question --- AGAIN - 04/06/13 04:34 PM

One more thing to do, I also put sealer in the channel the seal goes into. Make certain there are no scratches or marks on the crank's sealing surface where the seal rides. I've seen gouges there that would also cause a leak.