The clutch, as used on a Rotax engine in a military machine, is a bit basic in operation. It works... but can certainly be improved.
Old bikes are nice, they’re fun, they’re ‘our’ thing or you’d not be reading this… they can be improved… we have a look at a Rotax clutch.
When looking to make any improvements, you will need a few bits. As standard, the military Rotax engine Can-am has a fairly simple method of actuating the clutch. Inside the case there is a ramp cast and this has three piddling little ball bearings in it. A pressed steel fabrication rides up on the bearings as the lever is pulled. It works well enough on the road and even on a trail ride, but in the cut and thrust of an enduro, things get a little tougher.
Last year’s Hot Trod Vinduro was the final straw for my clutch hand, as I realised by the end of the Sunday all I was managing to do was take up the slack in the cable rather than lift the clutch. The Can-am gearbox is a robust thing but even so it goes against the grain to abuse mechanical parts in such a way for too long. Something had to be done.
One of the advantages of the Rotax engine is the number of companies who have used a variation of it to build their own machines, rather like Villiers engines of years ago, so there is a wealth of information around, plus a few special parts here and there.
Asking around, general opinion was the Aprilia version of the actuator was the way forward and once the bits were on the bench it was obvious this was a more meaty method of working the clutch.
The Aprilia kit requires the original ramp to be machined flat so the new base plate can sit squarely. Such work is beyond my workshop capabilities so a machine shop was sought and a large milling machine made short work of the ramp and soon everything fitted into place. A little light relieving on the central hole to make sure nothing was sticking and I looked forward to a simpler life for my clutch hand… until it dawned the Aprilia clutch cable enters the case at a different point to the Can-am and the operating arm is slightly out of line with the hole in the case.
Actually the Aprilia uses a different case which would have been an option but this would have meant converting to pre-mix and I wanted to retain the auto-lube facility of the original. Also the Aprilia style clutch case is rather rarer than the Can-am one. Luckily, my machinist said it’s not a problem to alter the actuating arm and all would be well, but after that it was my job to sort out the face spring.
Drain the oil out – be careful not to undo the kick- start spring instead of the drain plug. If you do, the engine needs to be stripped to reassemble it. There are precise lengths to Can-amcase screws, get them wrong and the screw will punch a hole in the inner casting, which is bad. This bit of cardboard with a basic case outline will ensure the screws are in the right order. Behold, the clutch. It’s worth cleaning the plates too when you’re this far in to the primary side. They can get sticky so a few moments with some clutch cleaner is worth the effort. The original clutch actuator can be seen here, it’s held in place by a spring and the arm return is helped by a coil spring. In the ordinary world it works, is a bit heavy but okay, in an enduro with constant usage it gets tiresome really quickly. These piddling little bearings are not really up to the job, even with constant lubrication they can stick in their recesses and then all the face cam can do is slide rather than roll. These 10mmdiameter balls used on the Aprilia version aremuch better and will allow a lighter movement as the actuating arm is longer too. The end where the nipple sits will need a tweak to hold the cable the other way though. This bad boy soon shifted the original ramp and allowed the case to accept the backing plate from the Aprilia kit. Once the machinist had finished it was a nice press-fit into the case. Note the tapped boss still in place so the clutch adjuster has the standard amount of thread to screw into for maximum strength. This didmean the rear of the backing plate needed relieving a little so it could sit flat inside the new recess. And here it is, sitting in place. It was at this point the realisation dawned that the part of the arm which holds the cable nipple wouldn’t be in line, or at least not as nicely in line as it could be. So, a little modification after a few seconds’ thought, by the talented machinist and welder who did the fancy stuff, while I stood and nodded sagely. Here it is in place. Yes it works, only slight cloud is the face spring, if anyone knows of a spring stockist with a selection of small springs then please let me know.
Above: Simply remove the kick- start, gear lever, all the case screws, footrest and brake cross- over shaft, then the case slips off easily… with a bit of wiggling.