I'll grant you they don't look great!

Weight is a non issue what with carbon fibre these days. Even ABS would be light enough - especially if you compare it to carrying a Scottoiler and oil round the planet with you! (and yes I know it'd be unsprung weight...)

I don't think the flappy chain thing is that big a deal either, since it has to join the sprockets at both ends, so it wouldn't be too bad making the unit big enough to accomodate the bow in the lower run.

As for the shaft drive idea, it's a damn sight heavier than any chain and case! Works fine for my K1200RS, but not on an off roader thankyou.

I wonder if there's a product which could withstand the constant rubbing of a chain which could be made into a kinda 'tube' for the lower run. I'm thinking heavy duty canvas? Kevlar? Cordura? Something flexible which attached to the frame / swingarm at the front, and simply encased the lower run down as far as the rear sprocket.

Yes, I have mad ideas from time to time...

Dave.... I'll watch out for you on Dragons Den

Rib the ABS tube like a vacuum cleaner hose or plastic conduit. No need to be tough so long as it can get out of the way. A ribbed tube can be thinner and therefore lighter too, plus the ribs trap grease and add an additional barrier.

What you can't do is add it as an afterthought. The MZ one works because of the flanges on the back of the motor and the ribbed/bellows section at either end. Nothing gets in, the grease in there is as fresh as the stuff in the rest of the engines enclosed spaces. The Harley version and other add ons fail because they try and use gravity to hold the case up to a motor.

I'd need to look in detail, but I'd also bet you could make a lubed chain smaller. There will be a safety factor that assumes an open chain will be rusty and worn out. If you are sure the chain won't get to this state and will be enclosed if it does fail in steel wire running round the case you have two choices. Either use an industrial chain the same size (cheaper) or use a smaller motorcycle chain. The weight can come off if it's that vital at the design stage.

Shaft drive is fine on Moto Guzzi's, Urals and Honda's where they control the lubrication and think about how it will wear. The BMW spline thing is garbage, even if they fitted grease nipples.

Andy

Interesting idea, hadn't thought of that.

Surely anything is better than nothing in sandy conditions. Providing you keep it dry, then it won't be trapping grit?

Does anyone know what the actual tensile strengh of a chain is, and how much loading it is able to sustain? (ie, it would pull a two tonnne car and usually has 500kg of force applied when cruising)

Dave- info for you re: DID -X ring chains
Standard tensile strength T.S) of 7,200 lbs
V O Ring T.S of 9,600 lbs
VM X ring T.S of 8,050 lbs
Z VM X ring T.S 10,400 lbs

O.E chain on bm wobble 'U's are made of chocolate (aka really cheap and nasty ones IMHO) but their steel sprockets are very good- go figure!

Very happy with my DID X 520 VM chain on my F650 Dakar

and I have to disagree with "Surely anything is better than nothing in sandy conditions"
Keep it dry dry dry, and maybe a brushing to dislodge surface grains of sand is fine at the end of each day's riding but no lube, no chemicals- no nada!
A good chain roller also helps-

Tensile strength is part of the issue but is really just how the chains are rated. You could tow or pick up your bike with a length of chain from the average mountain bike. Look at the mechanism on a fork truck or bike lift, it really is bicycle chain. What motorcycles have an issue with is impact loading (when you go from full throttle in first to the brakes), fatigue (repeated loading) and vibration (smaller parts have a natural frequency nearer where a bike revs). The F650 at 50 HP is probably as bad on a chain as say an 80 HP F800 because the single cylinder motor vibrates due to the single big pot, produces power in a lumpy way (one big pop in 720 degrees of crank rotation) and having less power probably has it applied in bigger doses. You won't snap the plates on the chain or collapse the pins as you would in a tensile test (big hydraulic puller snaps it), you will wear the pins or holes until the pitch isn't constant enough to work by repeated small loadings. Grease held in there doesn't make the chain stronger in tension, it prevents the wear by acting to "float" the pin in the hole.

The O-ring and X-ring chains have higher rated tensile stength because the materials are designed to work when lubed, as are the tolerances. I'd bet the pins are tighter in the holes so the compressed seals work. There is also IMHO an element of higher tensile strength looking better that a story about grease on sales literature, so design fudge factors that go with the seal set up are expanded upon to give a readily understood reason why one costs more. I'd bet if you tested any 520 chain it'd take over 10 tons. DID won't tell you than in case your application hits 9.5, does a sudden jerk and breaks one.

From memory (The last time I was a mechanical engineer about 15 years ago), the size of chain used on a 50 HP bike, in an oil bath would be specced for a 250HP electric motor. The tensile strength is still easily enough, but the wear is almost zero due to lube and smooth power delivery.

The chain case holds the grease, so you don't need the spray on lube, o-rings and so on. If the chain case leaks the grease will wash out leaving you with an unlubed chain, or sand will get it leaving you with contained grinding paste and probably a worse case than an unlubed open chain. Fitting a dry O-ring chain in a case is better until the case fills with sand, then it's worse. To me if you cover the chain it wants to be done fully and packed in grease.

Andy

Thankyou gents, most informative!

I'll keep the wet stuff for chucking down my throat then.