Crankcase sealant
Up to Commando
Has anybody any historical evidence to favour a particular sealant to use between crankcases? I think I last used a silicon based sealant, probably Hermatite instant gasket. That was 25 years ago, and that was the flavour advised by the "Service Notes". The other options on my list are Hylomar or Welseal.
Mick Hemmings recommends Wellseal and I think he mentions it on the Twins DVD.
The Hylomar formulation appeared to change quite a while ago and in my opinion has never been as good since. It is still not bad for paper gaskets though.
Mike Pemberton in his Singles DVD uses a high temperature silicone product designed for the plumbing industry to use on boiler flue pipes. It is called Plumba-Flue.
I also use another high temperature silicone, Loctite 5920 which has a sufficently high rating that you can use it to hold exhaust nuts in place, avoiding holes in the nut fins plus the use of springs, wires and other associated works of the devil.
I recently had an opportunity to use the Wellseal, its not a bad way to go, but I much prefer the "Yamabond". I feel it provides a superior bond & as a bonus is a nice gray color that matches your cases if you get sloppy. Remember you dont need much, just enough to thinly cover the surface. You can buy the Yamabond online or from any Yamaha dealer. Maybe the New Norton factory will sell Nortobond 
Skip Brolund
I will probably be shouted down, but I like silicone RTV. The cases have to be clean and oil free, and throw away the stupid nozzle which is supplied with the tubes, just smear on a very small amount with your finger, not enough to squeeze out when the screws are tightened.
I think RTV got its bad rap because people would squirt on a fat turd of the sealant with the nozzle, it would then squeeze out both outside and inside the engine, the stuff inside can block oil ways if (When?) it breaks loose. The other thing was that Hermetite used to supply bright orange RTV, and it was said that: "Orange gorilla snot is the sure sign of a rat bike".
I'm afraid I also 'stick' to silicon gasket, the kind that comes from B&Q, high modulus stuff, no need for costly automotive stuff in tiny tubes. As Colin says, use it sensibly spread to the outside of joints, well away from drain holes and the like and its fine. It stands up to heat, oil and fuel OK when compressed between joints. However most important are good flat joints with no nicks. Oh and low crankcase pressures, so good breathing is a must.
Greetings, unfortunately not al products are available 'down under' WellSeal being one of them. So the ThreeBond products are the go here for me (They make Yamabond http://www.threebond.com/) However Loctite (Henkel) may have a solution such as Loctite ® Aviation Gasket Sealant......You pays your money...
