I have a problem that is really exasperating on my 460. I have had this truck for over 30 years and the thing has always had a leak from the rear main seal. The leak was just a drip and was just annoying, so I just put up with it. After 240,000 miles and increasing blow by I decided that an overhaul was due. I had the block bored 30 over, I installed new sealed power pistons and rings. I took the crank to the machine shop to be ground. They said the crank was perfect and just polished it. New cam, cam bearings, doubler roller chain, Clevite main and rod bearings. I put the new rear seal in just as the service manual instructed. I used the Permatex Ultra black gasket maker for the sealer and put it on just as the book instructed. No leaks for 300 miles and then the darn thing started leaking again. This time it was no longer a drip. Even the starter was filling up with oil. I pulled the engine back out again and replaced the seal again. This time I noticed that the entire seal was covered with oil except for the wiping surface. Thinking that the oil might be leaking around the groove I cleaned the grooves very carefully and put sealer in the grooves. This time I put the ends of the seal flush with the block instead of offsetting them as the book shows. I put sealer on the ends of the seal thinking the oil might be leaking through the ends of the seal. Another 300 miles and the darn thing is leaking again. Sorry to be so long, but I don’t want to have to rehash things I already did. Has anybody had this problem, and if so, what was the solution?

 

What weight of oil are you using? My camaro will leak if I use 100% synthetic, If I use a blend or just straight Castrol GTX 20-50, no issues.

 

You need to check the seal crush before putting it together. It should have around .020 on it. Before putting any crank in you should always put the seal in alone, tighten the cap down and measure the seal for roundness. It sounds like you might have to trim down the ends of your seal some, if there is too much crush the seal will leak. If all else fails you will have to tear it down and put a rope seal in it.

 

You know that is a thought. I didn’t even think about the oil. I have been running Chevron Supreme 10-30 as a break in oil. I planned on running it for about a 1,000 miles to assure a good break in and then change to the regular oil. I always used Castrol 20-50 in the truck throughout the years and I think it is the reason that the crank was in such good shape after 240k. The amazing thing is that it went 300 miles after the rebuild before the seal started leaking. I pulled the engine and put another seal in and it went almost another 300 miles before it started leaking again. Changing the oil is definitely easier than pulling the engine again, so I am going to head for the parts house this morning and pick up some good old Castrol 20-50 and change it out. I will post the results. Thanks for the suggestion.

 

I am going to try the oil change first and hope it works. If not, then the engine will have to come back out and I will follow your suggestion. Thanks for the input.

 

Glad I could help, let us know how it goes.

 

Another thing about Fords, 460's in particular. Did you change the PCV valve? They build up an unbelievable amount of crank case pressure. If it were me, I'd change the PCV valve and add another breather. I bet the problem goes away. I've seen that work many, many times when people were convinced they needed a rear main seal. Just something else to think about.

 

I've replaced mine twice now and still leaks. There is a good thread over on 460ford forum that talks about the seal crush as Mike stated. It seems to be a very common problem with seals these days and over hauled engines. First time I offset the seal, 2nd time I made it almost flush on each side and for the 3rd time I'm going to try and take my time and make sure I have the right crush depth. I don't want to pull my engine hence trying to replace it with just dropping the pan. If it leaks a 3rd time, I'm going to pull the engine.

 

I had a similar problem that drove me (and everyone whos house I parked in front of)insane.

I pulled the motor(because I had to unfortunately),changed the seal again,and this time pulled the dist and primed the oil pump.Once it built up pressure,I looked at the back of the block.Oil puking out of a loose galley plug!It was never the seal in the first place.

 

Sorry I haven’t been able to get back to this earlier, but I don’t have much to report. I changed out the break-in oil and put in Castrol 20/50. I got underneath and washed all of the oil out of the bell housing and starter as best I could. My wife and I took a 90-mile trip and there was just a little weeping of oil on the bottom of the bell housing when we got back. It is not the heavy flow of oil that I was getting earlier. I am hoping that it is just residual oil that was in the bell housing and wept out when the engine warmed up. My wife got seriously ill after that and I have been busy with her every since and haven’t had a chance to do anymore with the truck. I will take the engine back apart and redo the seal as Mark A says if the leak continues. The last time I pulled the engine to replace the seal I did pull the dizzy and run up the oil pressure with the flex plate and the rear plate removed to make sure the oil wasn’t coming out of the cam plug or the galley plug. There were no leaks. Again thanks for all of the advice.