Primary Drive Oil Bath Seal

Removing the mastic sealant can be an absolute mare,especially if it was one of the best grades(dow corning etc) , You may have to lay the bike on its side for a few hours of scraping. I use a non setting oil resistant sticky silicone Red Rubber grease ,bought in a £8.tin. Works for me.

You do need to get rid of all the old silicone, as I discovered the hard way. A chisel and a Stanley knife blade will do that. I lie down on a Seeley mat, easier than laying the bike down! The rubber seal supplied by the NOC spares is about an inch too long, so cut it, offer it up and mark it for cutting off a piece. Drill or punch two or three holes in each end, dab on Superglue and wire the ends with copper wires twisted to tighten the join.(Strip out a bit of surplus domestic cable for suitable single-strand wire). Flatten the twisted ends into the band. Fit the band onto the cleaned inner case with the lip on its outer edge to ensure a seal with the outer case. I stuck the band onto the inner with an RTV seal, to keep it in place when removing the outer in future, and left it overnight with two clamps pressing a steel strip along the bottom edge to ensure oil tightness, as it may sag there even if you have shortened it to a tight fit on the inner case. Check the outer case is flat, laying it on the floor. If it is distorted you can bend it back by laying it across a 4 inch strip of 1/2 inch ply and standing on the ends! Then coat the outer case sealing area as recommended by Robert Tuck, and it slides on a treat. Check it both ends. You then embark on the fiddling around with the centre nut, its washer and the foot-rests, but resist the temptation to tighten the centre nut, just a thread showing should do. Now after three attempts it is oil tight using this method. 

Someone should make a replacement case in alloy!

A 500g tin from Granville £11 delivered ,E-Bay is all you need. Does both jobs for me.

There seem to be at least two types of band. The Singles have wedge shaped band which is a little shorter than the one on the Dommie. The Dommie one is the rectangle with a lip to be placed on the outermost edge. Two singles and a twin now...and they all leak to a greater or lesser extent. Every time I convince myself that one of them now fits perfectly, I find myself disappointed.  The latest machine has what seems to be a perfectly fitting case and cover, and is the worst of the lot. I'll try my spare Dommie band when and if I find it again, but I think it's too bulky to fit the Single. 

But don't glue it on all faces, or you will have to spend hours with a bent steak knife cutting it off again....

I have to admit that I have spent plenty of time getting everything correct. Straightening the cover,grinding back the cover to clear the prop stand bracket, sealing the cable grommet, forming a mastic oil shedder above the clutch shaft ,re-routing the breather to the tank.. The Red grease however was the final key to solving the issue. Now I get oil drips from the rear chaincase showing the Scottoiler is doing its job!.Hooray.

I bought a long pattern rubber seal with the lip from RGM, the only one available. Cut it to length and used cyanoacrylate to fix together, fitted lip facing in with lots of ordinary grease to my 1950 ES2. Was a firm push to slowly ease the cover on.

Result - no leaks after 100miles with 200ml of 20W in there! Astounding. I keep looking at it waiting for oil to come out but nothing.