Some time ago we talked tech stuff here… and it seemed OK..so while we are waiting for the cold…
Next time we will show you how we built a custom jack-shaft tool to change out the Ski Doo QRS helix without removing the jack-shaft.
In order to stay in the technology and buddy loop, we picked up a 146″ srviper form Bracebridge Yamaha
So to get to coupling this is what the skid does. (skid dynamics will be another article) First…The rear spring and shock is called the rear, the front of the skid shock – spring is called the middle the skis shock spring is called the front
When the throttle is pinned…the force of the rotating tracks rotation pulls the skid violently forward. This forward motion has to go somewhere…so it then pushes done hard on the middle arm..pushing the front of the skid into the snow for launch. The length and angle of the middle arm is designed on HP and application. (more on that another time) as this motion continues the back of the sled squats. The strap and other geometry happens at that time as well.
So..with coupling..see the stop on the Yamaha picture…..once the back scissor hits that stop…it sucks up the front of the skid. And then..that middle shock – spring begins immediately to work with the rear spring. So..to better understand. If you took out the middle shock and replaced it with a flat bar of steel..the skid would stop moving into compression the moment it hit the coupling block.
In other words the middle spring is designed to work with the rear spring on coupling.
Why do we need coupling..well coming off a turn ….you gas it without coupling the skis would lift and you may go straight..coupling simply keeps the skis somewhat on the snow by sucking up the front of the skid. Most sleds today have deleted the front to rear coupling. This was tried in snocross racing to stop “kick up” but I don’t think it is used anymore.
So why can’t we just shorten the strap to keep the skis down…Well you could ,,but then they would be dragging 100% of the time. The clutch would not like that loss (more on that later) and fuel mileage would suffer as it would be revving higher.
I have an excel chart, somewhere, that we made several years ago that graphs the skid motion on coupling every 10 mm thru its range. But I can’t find it yet.