CC006 POST-WAR OIL LEAKS/CHAINCASE

Is it better to fit a band-type seal to the chaincase on the bench before putting the engine/gearbox in the frame? - David Royston 4/12/2004

No, it would be even more difficult to put the whole engine and gearbox assembly into the frame after fitting the primary chaincase, and almost impossible if the top-end was on the engine.
It is quite normal to have only a mm or two of clearance between the bottom of the seal and the frame rail - just enough to slide in the band with a bit of twisting and using its curvature. There's seldom room to just put it on as a loose band but with the screw engaged, which is a shame since it's then a bit fiddly getting the screw in.
I have found it helps a lot to re-set the band around the chaincase before putting the seal on, aiming to closely match the outline of the case. The bands as supplied are usually a very different shape to the periphery of the chaincase, but it's easy to rebend them in your hands. Then you pop on the seal and slide the band around, engage the screw, and tighten the band in small steps re-settling the seal each time and pushing the ends ever closer together (with the gap somewhere at the top of course) until as the band finally feels tight all round the gap is almost zero. From experience I know how much the gap can be closed up so how wide a gap to leave as I cut the seal to length before starting. I guess it's about 5mm. So the seal is then really snug and the band is applying equal pressure all round.
If the paint on the edges of the cases isn't chipped there's no need for any sealant. In fact a hard setting sealant might be more likely to create an "oil-gap" over time as heat and vibration move the rubber and the cases around.
Assembled as above the joint stays oil-tight, even when the rubber turns to a sticky gum after many years. - TW 4/12/2004