<DIV> <DIV>G'day all. </DIV> <DIV> </DIV> <DIV>Apologies for the length of this post. It's a bit of an engineering diatribe and will probably bore the bejesus out of most normal people!</DIV> <DIV> </DIV> <DIV>I've been reading through this thread with interest, especially as I have the primary drive cover off my 1200 (waiting for new clutch rubbers and gasket to arrive in the post) and have been contemplating the age of my triplex primary chain. I have no idea how much work it's done, so was toying with the idea of getting a new one and keeping the old as a spare.</DIV> <DIV> </DIV> <DIV>There's heaps of triplex industrial chains available from various manufacturers. As a mechanical engineer, I like to look at the engineering specifications, and there's not much difference between Reynolds, Tsubaki, Regina, and a bunch of Chinese manufacturers (actually, some of the Chinese claim to be higher spec than chains made in USA - but I take that with a grain of MSG). Anyway, the specs don't tell us much on their own. What do they really mean?</DIV> <DIV> </DIV> <DIV>If we look at the static load, we find that the rated working load (not tensile strength) of a typical 3/8" BS triplex industrial chain (to fit a Laverda drive) is about 5000N. The tension imposed on the primary drive chain of a Laverda triple engine is around 2000N at peak torque, which is well within the working tension of the chain. So far-so good. </DIV> <DIV> </DIV> <DIV>However, it's not just a matter of looking at the static tension in the chain and picking one that will take that load. A power transmission chain is a dynamic thing, you also have to look at sprocket size, chain speed (m/min) and power (kW) transmitted, then there's a whole bunch of design factors like fluctuating load factors, shock load factors, speed factors, acceleration factors, sprocket size (teeth factor), multiple strand factors, inertia ratios, environmental factors, etc... so you can see that it gets rather complex. </DIV> <DIV> </DIV> <DIV>Cutting to the chase, when you go through all the design calulations, you find that the rating of a 3/8" triplex chain operating on a 25 tooth (=Laverda crank) sprocket that rotates up to around 7000rpm is about 3kW. This is bad news because unless your bike is very sick indeed, it should be making more power than that. </DIV> <DIV> </DIV> <DIV>So where did all the chain strength go? It got eaten up by the speed that the thing flies around at. The design charts give a maximum operating speed for 3/8" industrial chain of 120m/min. On a Laverda it's travelling at about 1,600m/min which is about 13 times its design speed! So it's way off the chart. The reason speed has such a huge effect is that the chain has to zip around that little crankshaft sprocket, and all the inertial forces related to the change of direction are added to the drive forces that it has to transmit to the gearbox. So speed really does kill - chains at least. The designers at Laverda were well aware of the chain's shortcomings, and even a higher spec chain (if that's what the OEM chain is) is still woefully inadequate. So that's why the Laverda manual recommends tossing them in the bin every 20,000km. </DIV> <DIV> </DIV> <DIV>All of this begs the question - why did they opt for a roller chain in the first place?</DIV> <DIV> </DIV> <DIV>If they couldn't fit a gear drive in, then Morse hy-vo chains are much better suited to this application. They're twice as strong in tension, have higher speed ratings, are less subject to sprocket (chording) stresses, are quieter, lighter, and more efficient at power transmission than roller chains. If you look inside the engine of a Japanese bike with chain primary drive, it'll be a morse chain and it will last as long as the other engine components (my 1985 Kawasaki 1300 has a Morse primary chain and has done over 100,000km - most of that towing a sidecar, and there's no slack or wear evident in the chain)</DIV> <DIV> </DIV> <DIV>It seems there are several belt drive conversions around, but has anyone fitted a Morse chain primary drive to a Laverda?</DIV> <DIV> </DIV> <DIV>Belt drives are about half as strong as roller chains in straight tension, but they're much lighter so the dynamic stresses are very much less. The cyclic bending and straightening of the polymer matrix and load-bearing fibres causes heat and fatigue, and it will eventually fail. So the belt needs to be replaced regularly. </DIV> <DIV> </DIV> <DIV>When you consider that the primary drive is in an oil bath, a Morse chain is (in my opinion) by far the best engineering option. Dunno about the cost as an aftermarket modificaion though - maybe I'll look into it some time.</DIV> <DIV> </DIV> <DIV>Cheers</DIV> <DIV>Cam</DIV></DIV>