The rear main seal in the 426 wedge in my 64 Polara has pretty much leaked from day 1. I have replaced the seal several times.... last time I put in the Mancini billet saddle and seal, and a new Milodon pan, but it still leaks. It occurred to me last week that I had installed a high pressure oil pump when I built the motor, which carries 75lbs going down the road. I thought.. That's it! So I went to Jegs and got a high VOLUME pump and installed it. STILL has 75lbs on the road and still leaking. I have no idea where to go from here. Am I overlooking something obvious?

Could it be coming from another source? Oil pressure switch/gauge pung? valve cover? crack in the block? oil pan? Did you run dye thru it yet?

was the engine block line honed and or line bored at 1 time?then you need to take some material off the seal bridge.

I have no idea if it's been line bored... I was told the block was a race block for a 65 Satellite named Alias Smith in the 70's, so I guess it's possible. The oil is leaking right out between the pan and inspection cover on the bellhousing. I'm pretty sure it's not coming from the oil pressure fitting and the crank is a stock crank from a 413 I have. I never considered taking some material off the main cap. I suppose that would need to be done by a machine shop, but how would you measure how much to remove?

Well, if it has been line bores, then you can't take anything off the cap, as it will already be sunk into the block centerline, just as a timing chain comes in undersized models. Youll have to add some RTV or even a second strip of gasket material to the top of the rear cap to compensate for the uneven surface. Does Someome make that spiral beveled bearing that pushes the oil away from the seal or is that a smll block thing? Dont rule out the cam freezeplug or the oil galley plugs behind the trans, or even a leak that finds its way to the lowest point of the motor. Get yourself some fluorescent dye and a black light penlight and start hunting after hours or in a very dark garage.

What Pishta said w this many tries I'd get a dye kit & pinpoint the loc exactly then a good visual during dissassembly to ID the prob

Line boring only affects the crank main bores , the cap mounting face does not get machined .

What kind of seal?,....rubber, rope?

Is the crank seal journal smooth or serated?

have you tried one of the improved oil seals that member 'roadhazzard" makes?

his has fixed this on a few engines from the post I have read here on Moparts

worth checking into after this many times R&R-ing it.

The seal is rubber and the crank is smooth. I never even thought to check the back of the motor last summer when I installed a new clutch.

99 times out of a hundred, if the stock cap is retained, it's human error.

There used to be a "anti-leak" rear main bearing available for big blocks. I don't know is it really worked or if it was just marketing.

This has several " options" as to what could be wrong. Its never clear without seeing it in person, but that being said, here are the common mistakes:

1) Seal in backwards
2) Seal retainer wasnt lined up with seal grroves and/or checked
3) Rough crank surface
4) Side seals not all the way down in the slots, OR , protruding from top of seal retainer. Overall mis-installation of side seals.
5) Spot facing needed where the bolt heads rest inside the cap, Errosion etc often leave the caps cockd because of wear there.Spot facing of bolt bosses does help.
6) Seal retainer ends need to be cut in a cap grinder to be squared and add a slight bit of tension to seal
7) Oil pan bolts too long and tighttned too far, cracking open the " wells" in the seal retainer, and oil leaks out the threads.
8) As mentioned, two different " planes" between seal retainer and pan rail where the retainer and block meet. Oftn a good gasket seals this up.

Many times a seal is to blame, but it can also be the side seals, the oil pan bolt threads, a misfitting retainer and also sometimes simply filling the groove ont he OUTSIDE of the seal retainer to the block will stop what is believe to be a bad rear main. I only use Superformance and Fel Pro 2904 seals. Stock ones will work fine, but never as good in my opinion as the Viton style. You also can have problems when a seal surface has been polished too much, or is too rough. Sometimes a slight polish helps, but its a good idea to cut the retainer to add some pressure afterwards. The old anti leak rear main bearings did work, but you really shouldnt need one if everything is correct. You can also switch to a rope seal, and often times it will resolve a problem, or at least band aid it. Again, if you know what to look for, and how to do it, rear mains dont and shouldnt be a troubling leak.

Long shot,there were some cranks, typically marine cranks that ran reverse rotation and had the seal serrations backwards! Doubt thats the case here, just saying.

Good luck.

You dont make the bores any bigger than the required specs, which have a low and high limit. The reason the bores arent " expanded" is because tyhe first thing you do is cut a few thousands of an inch off the feet of the main caps. The makes the bore " smaller" to start with, then you bore or hone ( two completely different things) back to the spec size. I prefer to hone to the low limit, which gives the maximum " crush" on the bearing shells. The bearings shells ( outer) dont change, they are all the same size. If a shop does the job RIGHT, they take minimal material off of the block sides ( saddles if you will)of the mains, so as to not change the crank to cam centerline very much. If someone doesnt do it this way, they then change that dimension, and if its been done several times wrong, thats where your " minus" timing chains come into play.

The crank should have the diagonal hash marks where the seal rides. If it's an old marine crank they are going the wrong way and this is the problem.