[2+2=421]

Just had my engine rebuilt, 3 months back, maybe 300 miles and leaking from the rear main seal. Machine-shop used 1 piece viton seal. I asked them what the deal is and i get.. well sometimes the never leak and sometimes they do.. what is the machine-shops responsibility in this? I know they wont pay to r&r the engine, so whats standard protocol?
Also when i replace it do i use a two piece seal? Not interested in removing the crank etc., very frustrating!!

[shaker455]

One piece works great and i've had good luck....I would say one of the best seals out there.
I have used many seals including a Caddy for a stock 455 crank.
What crank are you running?
I don't think your going to be able to remove the seal without lifting the crank some.
I usually do a tilt test with an engine crane to test the seal for leaks.

[dataway]

Possible it's not the seal itself but the joints where the pan meets the seal and the block.

[steve25]

Your going to atleast need to drop the trans off and flexplate, then spray out the whole seal area with Carb cleaner to dry it out and then really jack up the nose of the car and remove the oil filler cap.
Then you will likley see where the oil is really seapping from.

Hopefully is from around the OD of the seal or the pan gasket area and you will be able to spray it dry again and then pack it with gray form-a- gasket and let it set up for 2 days and the reassemble with the trans out and start it to see if your golden .

[Cardo]

I chased this oil leak for 6 years and pulled the engine 3 times before i found it. Make sure you check this! https://forums.maxperformanceinc.com...d.php?t=471237

[TedRamAirII]

Most Rear Main leaks....the front of the flywheel/ flex plate will be wet from the oil being slung. So I would clean it off really good with a spray Brake Cleaner, and run it and make sure it really is. Its a tough area to see, if its the oil pan gasket, rear seal, or the seam between the black/ main cap. I think the Machine Shop would be obligated to pay/fix the repair....If they supplied the seals / gaskets.

[Richie Hoffman]

Recheck oil pan bolts gasket can shrink from heat cycling and can seep oil check easy stuff first before going for the big stuff

[Cliff R]

I agree to verify that it actually is the seal and not the pan or something else.

Using lip-type seals on factory cranks is hit and miss. Factory cranks have serrations cut in them to help the rope seals work correctly. Sometimes they are cut pretty deep and if the lip seal lines right up on them they will leak every single time.

I always do a mock-up with a lip type seal before deciding whether to use a rope seal instead. For most engines I've done with factory cranks I've used the Best rope seal and never had one drop of oil get by one. For aftermarket cranks I always use the Viton two piece seals (custom fitting required), and never had a leak with one of those to date either.......Cliff

[2+2=421]

Stock 421 crank

[lust4speed]

I prefer mineral spirits applied with a spray bottle over using brake cleaner. It pretty much leaves the paint alone but does a good job of attacking oil and dirt.

Not foolproof, but if the oil is on the flexplate/flywheel and the crank flange is dry after cleaning and running the engine, then the leak probably isn't at the seal lip. I pulled one engine down to correct problems from a previous shop's build and someone had filled the bottom of the groove with silicone before dropping in the one piece seal. Instead of the seal displacing the excess silicone, it distorted the seal with pockets of silicone holding it away from seating properly and allowed the seal lip to pull away from the crank in some areas.

You have to be careful with flattening the area where the main caps register. It's fine to find and remove particles that ended up there after machine work. If it is the actual cap or block surface and the line hone was completed with this rough mating, then removing material is going to tighten up bearing clearance. Bearing clearances are a little less than the width of a human hair and you really don't want to be smoothing bumps out unless you plan on a new main journal line hone.

[mgarblik]

For these tough situations I strongly recommend using an EVAP emissions smoke machine to verify the exact location of the leak. You can do this with the engine in the car and no damage to paint and so forth. Remove transmission and flexplate or flywheel, hook the smoke machine to a valve cover and let it smoke away. In 30 seconds to a minute the exact location of the leak will be very visible. You can tell right away if it is the main seal, rear pan seal or some other unknown leak source like the rear of the valley cover, distributor and so forth. Then you know 100% for sure what needs to be done to fix it. These tools are pretty expensive, so possibly you can borrow one from a good independent shop or rent one for the day. Virtually every new car dealer has had one of these machines in the shop for 20 years or more. Good luck with the diagnosis and repair. BTW, if the stock 421 crankshaft had the serrated seal area for the rope seal, that has to be polished to a very smooth surface finish to allow the Viton seal to run leak free on it. If it was left untouched, it has possibly ripped the lip of the seal.

[PAUL K]

Originally Posted by mgarblik

For these tough situations I strongly recommend using an EVAP emissions smoke machine to verify the exact location of the leak. You can do this with the engine in the car and no damage to paint and so forth. Remove transmission and flexplate or flywheel, hook the smoke machine to a valve cover and let it smoke away. In 30 seconds to a minute the exact location of the leak will be very visible. You can tell right away if it is the main seal, rear pan seal or some other unknown leak source like the rear of the valley cover, distributor and so forth. Then you know 100% for sure what needs to be done to fix it. These tools are pretty expensive, so possibly you can borrow one from a good independent shop or rent one for the day. Virtually every new car dealer has had one of these machines in the shop for 20 years or more. Good luck with the diagnosis and repair. BTW, if the stock 421 crankshaft had the serrated seal area for the rope seal, that has to be polished to a very smooth surface finish to allow the Viton seal to run leak free on it. If it was left untouched, it has possibly ripped the lip of the seal.

Great advice!

[TAQuest]

Affordable smoke machine:
https://www.amazon.com/STINGER-Smoke...90603233&psc=1

[steve25]

For 150 bucks before shipping I'll lend you my neighbor, he's a endless perverbal smoke stack with his two pack a day addiction, lol!

I think I would try find the leak first by draining the oil out, pouring in a gallon of WD-40 with some blueing dye added to it and then jack way up the nose of the car and do what I suggested to trace the leak.

[TAQuest]

Originally Posted by steve25

For 150 bucks before shipping I'll lend you my neighbor, he's a endless perverbal smoke stack with his two pack a day addiction, lol!

I think I would try find the leak first by draining the oil out, pouring in a gallon of WD-40 with some blueing dye added to it and then jack way up the nose of the car and do what I suggested to trace the leak.

What do you think wd-40 residue will do on your bearing surfaces?

[steve25]

Nothing once you drain it out, add new oil and then pull the plugs to allow cranking of the motor for 20 seconds.

[1968GTO421]

Originally Posted by steve25

Your going to atleast need to drop the trans off and flexplate, then spray out the whole seal area with Carb cleaner to dry it out and then really jack up the nose of the car and remove the oil filler cap.
Then you will likley see where the oil is really seapping from.

Hopefully is from around the OD of the seal or the pan gasket area and you will be able to spray it dry again and then pack it with gray form-a- gasket and let it set up for 2 days and the reassemble with the trans out and start it to see if your golden .

Originally Posted by lust4speed

I prefer mineral spirits applied with a spray bottle over using brake cleaner. It pretty much leaves the paint alone but does a good job of attacking oil and dirt.

Not foolproof, but if the oil is on the flexplate/flywheel and the crank flange is dry after cleaning and running the engine, then the leak probably isn't at the seal lip. I pulled one engine down to correct problems from a previous shop's build and someone had filled the bottom of the groove with silicone before dropping in the one piece seal. Instead of the seal displacing the excess silicone, it distorted the seal with pockets of silicone holding it away from seating properly and allowed the seal lip to pull away from the crank in some areas.

You have to be careful with flattening the area where the main caps register. It's fine to find and remove particles that ended up there after machine work. If it is the actual cap or block surface and the line hone was completed with this rough mating, then removing material is going to tighten up bearing clearance. Bearing clearances are a little less than the width of a human hair and you really don't want to be smoothing bumps out unless you plan on a new main journal line hone.

I, too, have leaks. Thanks for great advice!

[scott70]

Originally Posted by Cardo

I chased this oil leak for 6 years and pulled the engine 3 times before i found it. Make sure you check this! https://forums.maxperformanceinc.com...d.php?t=471237

I never knew that and was just over to my machine shop and he showed me where he actually sealed that ,he says that they always do that.he put a special red sealant in between there and not just silicone I guess

[gtofreek]

I always use an anaerobic sealer like green Loctite to seal the main cap to the block. Silicone can prevent the main cap from seating and cock it so the front half of the main bearing takes most of the hit and wear.

[Fdby6017]

My rear main is leaking....66 389 tri power....i fear going thru this repair...knowing it may leak again....had same issue many yrs ago on a different 66. Im considering motor swap to something more reliable.