I've heard the Mancini rear main seal kit is the best. Is this true? What would you recommend for a stock 440 rear main seal?

A stock crank should be knurled. That is always the first thing to look at. The other thing to pay attention to is if the rear main is currently leaking. Leakers sometimes are due to poor machine work and those can be hard to fix. Leaking caused by worn out parts can usually be fixed.

I have been using the billet Mancini seal for the past few years.
I still have leakage!
Mike

I just built a engine with a billet retainer and viton seal. Leaked like a sive. Replaced
It with stock retainer and a black felpro from the parts store and its dry as a bone.

If the crank has stock knurling, isn't it required to use a rope seal? Smooth crank surface gets a Viton or other material.
I thought the knurling would wear away a rubber seal quickly

I have the billet Mancini rear main and it doesn't leak a drop of anything.

I have one that just got dyno time only. No leak at all. Then, one that leaks quite a few drops after a drive (my buddies car). Both billet seal retainers.

Edited, I have had less leaks with a stock seal holder than with the race blocks and their brand seal holders
I keep the stock seal holder when I destroy or get a customer block in that is not savable They work really good

I always use normal Fel-Pro replacement rear main seal and the factory retainer. No issues.

How many of the "no leak" rear mains also use a vacuum pump or header e-vac ???

383/432 Stroker that I built four years ago - Zero drips - Street motor - Factory PCV and Three Nipple Breather 1971

I also use the Mancini Billet - Brown Viton Seal - Second motor that I built with great results

Seal clocked at 6 and 12 for me anyways helped align the retainer using those alignment studs

O rings on side of retainer with a little Permatex Black RTV


If I was buying today

I would probably look at Hughes Engines Retainer Kit - They have a pressure relief area built into the retainer like the factory unit

I have 3 of my own here...one has a vacuum pump. The other 2 just have breathers on the valve covers. Never been a fan of the header evac setups.

i had the samr results on a 520 ci.rb

We're jinxing ourselves even talking about this stuff. This discussion alone causes leaks. It's not good to talk about it.

I've only used the ones from old MP kits and Fel Pro kits.

They have all had a number molded into them: 4227926. I had to look really closely to see it.....(It's not hard to guess whos tooling they came from).

Avoiding snafus during install + the side seals seem to cause alot of problems.

Though the white "swells up when soaked in mineral spirits" side seals never really
gave me any trouble, I always thought they were a pain to install and I used up my last pair several years ago on a 440 re-ring.
don't believe they are made anymore (were they asbestos or something?).

So on a modern build, myself I substitute RTV for the side seals. I try to inject it inside the groove
as much as possible and also pack that area using putty knife/fingers and so on.

If I remember right, the new seals don’t align over the knules, it’s on the smooth part. They have to installed in the right direction too, bevel points into the engine, like a timing cover seal. And the retainer goes on DRY no oil film, sealer will not stick to oil. The whole area is sprayed down with disc brake cleaner.

I have used a thin layer of adhesive silicone on the back side to hold the seals to block and seal holder and i ALWAYS use wheel bearing grease on the lip edges of the seal and on the main seal area of the crank surface
I have never tried installing the seals and crank dry, NEVER

I did that on my current 451 and it worked perfectly. I just made sure to get the seal holder and the block operating-room clean before applying it.

I just bought and installed the Mancini rear main seal, and it solved my leak issue.

Me too. Customer had a bad leaker on his motor. It was a fresh rebuild that had cam and piston problems. Just finished it about two weeks ago. No more leaks with the Mancini seal. I also bought the extra cost orange seal with the billet cap.