TAPP Snowmobile Primary Clutch Tuning - Part 3 - The Ramps
In part 2 of our series on the TAPP Primary Snowmobile Clutch we talked about the shift arms and rollers and mentioned they interacted with the ramps. In this segment, we’ll look closer at the ramps themselves.
TAPP Clutch ramps are located and held in the moveable sheave by a mounting pin at the base of the ramp. The pin is secured to the sheave via two hex head screws. The windows in the cover of the clutch allow easy access to the ramps and they can be adjusted or changed without removing the cover of the clutch. Just remove the two hex head screws and the ramp pulls out.
Each ramp has two sides which can be used. As discussed previously regarding weight changes to the rollers, always install or adjust the ramps in opposing pairs. For example, you can have all 4 ramps on the A side, 2 opposing ramps on the A side and 2 on the B side, or all four on the B side.
As RPM increases above idle, the roller on the shift arm begins to push against the ramp. When the RPM is high enough, the roller climbs the engagement area of the ramp and pushes the ramp and movable sheave enough to engage the belt. As RPM continues to rise, the roller moves along the curvature of the ramp as the clutch shifts out.
The two sides of the ramp have different engagement areas and different curvatures. If you look at the picture of the ramp, you can see that the engagement area of the B side is substantially taller than that of the A side. It’s this increased height of the ramp above the mounting pin that gives the B side higher engagement RPM than the A side. We’ve made it easier to see the difference in the diagram that shows the A side imposed over the B side.
The difference in curvature between the 2 sides creates different shift characteristics. A steeper angle to the curve will require the roller to exert more force to climb the ramp and push it down to move the sheave and shift out the clutch. The extra force required means that steeper ramp angles will increase the operating RPM of the clutch. Lower or flatter angles will result in lower RPM. The B side will have higher engagement and launch RPM but will pull harder after that due to its flatter curve. The lower engagement with more controlled shifting of the A side is preferred by most trail riders and the higher engagement and stronger pull of the B side is the choice for a lot of drag racers.
Speaking of ramp curvatures and angles, that brings us to the ramp clicker bolts. I already mentioned the ramp is held into the moveable sheave by a pin near its base. The bottom of the outer edge of the ramp is supported by a 6 position adjustable clicker bolt. The shaft of the bolt is an eccentric which raises the outer edge of the ramp on higher number settings, 6 being the highest. Raising the ramp by turning the bolt to position 6 will result in the highest running RPM. Position 1 will result in the lowest RPM. Note that not all clickers need to be set the same. For example, two could be on 6 and two could be on 3. As with the other adjustments, it is important to keep the settings the same on opposing arms so the clutch remains in balance.
The clickers will have the most effect on the upper end of the shift pattern. If you look at the diagram, you can see that adjusting the clicker has the most effect on the outer area of the ramp because it pivots around the mounting pin, with only a little effect near engagement because there is less movement in the ramp there when the clicker is changed. Adjusting the clickers changes the angle of the ramps by raising and lowering the outer edge of the ramp, therefore changing the shift pattern and running RPM.
TAPP manufactures different ramps for different applications and we have tried several of them. In our experience, the 1328 ramps they provide in the snowmobile clutches are the best available from TAPP for sledders.
Tip: loosening the bolts that hold the ramp into the clutch will make it easier to make clicker adjustments. Just remember to tighten the bolts again when done with the clickers.
In the 4th and final part of this series we’ll discuss tuning theory for maximum performance.
