Honda Price Drop - SH Mode

[Argyll]

The little Mode is so quick up the hills that I contacted the previous owner to see if he had modified the scoot. He explained that he had installed a Malossi variator and racing clutch and also had a box of various rollers which I might want for my Sym Jet 14. Knowing next to nothing about how these things work I said that I'd investigate to see if I could simply change the rollers in the Sym, and whether it would be worth the effort. I doubt that it is but I'm really just a beginner with this stuff, even although I've had several scooters.

[roadster]

Personally my experience with Malossi parts was not entirely good but that was just one case on a 250 Yamaha some 20 years ago. Changing variator rollers is a more straightforward process. By using the Dr. Pulley or other specialist non-cylindrical weights performance and longevity improvements can be achieved. Cylindrical weights will in theory spread wear because they can rotate but in practice they usually develop flats and require service replacement. Specially shaped weights are actually sliders which don't rotate but are made of much more durable material. In some cases these weights will alter the final geometry of the fully closed variator pulley to give a slight increase in top speed but this depends on the tolerances of the manufacturers design.

The main performance factor which can be significantly changed is the gearing during acceleration. Original designs generally provide a ratio during acceleration which sits the engine at peak efficiency not peak power. By using lighter weights the rpm during this phase can be increased up to the point where peak power is sustained during full throttle acceleration. This is at the expense of fuel efficiency and arguably engine wear.

Because of the changed geometry Dr. Pulley weights are always recommended to be at least 10% lighter than standard rollers but owners can choose to go lighter for a performance vs fuel consumption improvement.

Changes to the rear pulley assembly should be treated more cautiously because there is both a spring loaded variable pulley and a centrifugal clutch incorporated. For competition purposes changes in clutch engagement characteristics are sometimes used but unless you are determined to leave the start line quicker up to about 15 mph there is little point in this. The other possible change is the spring rate of the large compression spring which determines the tension in the drive belt and this in turn changes the forces keeping the two halves of the front pulley apart. Getting this wrong can severely affect belt life so outside of racing circles its best avoided. Racers expect to strip there power unit regularly but you might not want to do that for general use.

Hope this gives you food for thought and perhaps more research. There are some youtube videos which show exactly how variator transmission behaves and a video is sometimes worth a thousand words.

[Argyll]

Very interesting @roadster. I was actually given 3 new sets of rollers today by the guy - 10.5 12.5 17.5 - so now to figure out which bike to experiment on.

[roadster]

Very interesting @roadster. I was actually given 3 new sets of rollers today by the guy - 10.5 12.5 17.5 - so now to figure out which bike to experiment on.

It is useful to have a rev counter for testing and it can also help to know at what rpm peak power and peak torque occur. Most engines have rpm limiters which prevent over revving but its not good to be bouncing off the rev limiter during acceleration and even worse to be causing valve bounce missfire if there is no electronic rev limiter! These risks will be greatest with the lightest weights ( 10 gm I assume ).

Let us know how you get on.

[Argyll]

The Sym has about 12.5hp and produces max power at 8,000 rpm (red line starts at between 9 & 10). Max Torque is 11nm @6,000 revs. I was going to try the 10.5g as I believe the oem size is 12.5g (although I'm not 100% sure). I generally like the bike the way it is but just want to play around with it to see what the difference is.