Main Seal Leak HELP !!!

[SOLSAKS]

newly built motor
shop that installed and machine shop have tried at least 3 times
to replace the rubber main seal

each time they were very careful
and did things as right as rain
but still leaks

they said they made sure all valleys etc were clean
( hope I am using right terms )

has anyone experienced this
that has advice ?

thanx
dave in NC

[Ristow]

probably not the rear seal. if the rear oil galley plugs were not sealed they can leak out back of block.

[wiley-moeracing]

can also be the rear seal on the intake manifold leaking down, and or valve covers, check both.

[Full Size Jeeper]

How sure are they, it is the rear seal. Lots of other things above it could be leaking. Cam plug at back of block could be one. Are you driving the truck yet? Oil makes the seal swell, thicker than when it is first installed, you need to drive it. Where the two halves meet, a small amount of sealer is recommended.
Mine had a little, leak at the rear main seal. Was never a drip, just wet in that area. It went away once I ran it through a few heat cycles. What about the PCV valve, is it working. Are the piston rings seated yet? Do you have to much pressure in the crankcase. Good luck.

[gophman]

Yup I have replaced the rms on my wife's waggy 3 times in place and still leaks like a mother so since this summer looks like a bust I'll pull the motor to see if it's possibly cam gallery plugs (I'd had them out to clean).
The irony is my 360 in my pickup with a fresh build is pretty much dry and I reused the seal lol.

[SOLSAKS]

thanx to all who responded
I will relay this to the shop

I will report back

dave in NC

[Carnuck]

There is a vacuum pump that can be hooked up to keep the oil from coming out.

[FSJunkie]

Or they are not doing it right.

I put Permatex #2 on the outside circumference of the seal where it fits into the groove of the block and bearing cap, on both sides of the tabs on either side of the seal, and on the split ends where the two seal halves meet. I do that and I get engines that do not leak literally even a single drop of oil. The trouble is, it's very hard to do it that way with the crankshaft installed.

It can also be an oil pan gasket not done right. Pans get warped and messed up by idiot mechanics. For those I use silicone sealer where the rubber seals meet the cork gaskets.

[Ristow]

Rear mains are typically pretty easy to keep oil tight. They used to use ropes for rear seals you know.

[DarkMonohue]

Make sure that the PCV system is in place and functioning correctly. The rear main in my J20 leaked like a son of a gun until I replaced the PCV hose behind the carburetor. The original hose had collapsed and was allowing crankcase pressure to build up rather than vent to the intake manifold, and the crankcase pressure pushed oil out past the rear main seal.

The original formed hose is NLA, and the bends are too tight to easily make with bulk hose, so I cheated a little and used a long enough hose that it formed a big loop. That allowed it to connect at both ends without being pinched or folded on itself.