650 SS primary chaincase

I am working on a 1969 Mercury and will be digging into the primary chaincase for the first time: servicing the clutch, etc.
I am pretty sure the chaincase is the same as on a 650 SS or Atlas.
I wonder how successful I will be putting it back together without leaks.
Is this a possibility? Or should I just get used to the idea that it will inevitably leak?
If it is near impossible to seal up the chaincase, I might install a belt drive.
I'd appreciate hearing from folks who manage to seal up the chaincase or installed a belt drive to deal with persistent leaks.

Stephen Hill

Stephen, I was unable to get my 650SS cover to seal. I also had ongoing clutch slip problems. The solution to both problems was to install a Newby belt drive.
A friend has a 1957 model 99 with standard primary. It looks to be the very same cover arrangement as on my SS. His primary does not leak a drop. One trick to help keep the oil in is to smear some general purpose type grease on the outer flat side of the rubber seal and to use a silicone sealant or equivalent on the inner flat side of the seal.
I tried these methods with mine, but no luck. Looks like a 50/50 chance yours will be dry!
Glen

It can be made to seal, although it looks like it is an impossibility.

Follow WornTorn's advice....bond the inner side of the big rubber gasket with silicone, RTV, or other rubber to metal adhesive to the inner cover. I use silicone on the outer side of the big rubber around the lower half....dont worry, the outer cover can be removed when necessary.

I did these further steps, although i am not sure they are necessary.

1) I drilled out the spot welds holding the sliding disc that moves with the gearbox mainshaft, splitting the disc into its inner and outer halves. I next installed an O ring inside the disc halves, and used small (4-40) screws with blue locktite to hold the disc halves together, tightening just enough to allow the disc to slide freely,

2) i spot-welded in a drip channel over the top edge of the sliding disc, so that oil would drip over, not between the disc halves.

The outer cover should not be overtightened with the big nut....one or two threads exposed is enough. If the PO overtightened, check that the outer cover has not been warped.

Sometimes the best i can do is get only one or two drops of oil per month, but i have had zero leaks at times.

Use Ford ATF rather than oil in the primary case. It provides 35% more friction on oil soaked clutch plates than oil, and has no bad effects on the rubber cushions in the clutch hub. Besides, if the chaincase leaks ATF, you will see red. Many times, oil from other places is blamed on the chaincase. Allow the silicone 24-48 hours to cure before filling chaincase with ATF.

Slick

If the outer chaincase has been overtightened at some stage, to the point that the case is fractionally distorted you will never, well hardly ever. get it to seal, with the standard set up. In any event do what slick said. Even a leaky chaincase can be made to seal, with care and attention to detail.
The 650ss, Atlas and Mercury chaincases are all the same apart from the finish, paint on the Mercury, chrome on the 650ss and I think the Atlas.
Best of luck.
cheers
wakeup