TAPP Snowmobile Primary Clutch Tuning Series - Part 1 - The Spring

Today we introduce part 1 of a series on tuning the TAPP primary snowmobile clutch. We'll start out with the most basic component that everyone is most familiar with, the primary spring.

This is a chart of the most common springs used in the TAPP primary. You can see in the chart, the Blue, Brown and Black springs have very similar "rates". This means the shift pattern is similar between the three but with the stiffer springs yielding a higher RPM across the shift range. The Red and Blue/Orange springs are higher rate springs in that they get stiffer faster as the primary clutch moves through its shift. You'll notice that these last two springs are quite stiff at full shift out and would yield a very high RPM. Because of that, they are not used very often in turbo 4 stroke applications.

How does a stiffer spring effect RPM at engagement? In the TAPP snowmobile primary, each 10 pounds of spring force raise the engagement RPM by about 100. If we use the Blue spring as a base line set up to engage around 3200 RPM, keeping all else the same and just changing to the Brown spring will raise the engagement by about 200 RPM to around 3400 RPM. Once again, all else equal except the spring, the Black would yield another 200 RPM increase at engagement to around 3600 RPM. As these springs all have similar rates, similar RPM increases can be expected throughout the shift range, ie the Black spring will have a higher full shift RPM than the Blue spring.

Of course there are several factors that can and will effect engagement and RPM, but in this brief discussion we are only referring to the effect of the spring.

Follow us and watch for part 2 in this series where we will discuss the TAPP shift arms.