Maxceleration Racing

TAPP Snowmobile Primary Clutch Tuning - Part 4 - Setup and Performance Tuning

In parts 1-3 we covered the components that can be changed/ adjusted on the TAPP Snowmobile Primary Clutch. In this final part of our TAPP primary clutch series we’ll discuss some setups and performance tuning tips.

Let’s begin with the most common trail setup with the 998 Turbo engine as an example. Most of these sleds with trail tunes will use the Blue TAPP spring and the +1 rollers. Ramps should be set to the A side. Weight can be added with Allen Screws in the swing arms to refine the RPM as desired. Start with the clickers in the 3 position and adjust as desired. This is a great baseline that will yield smooth engagement and excellent trail manners.

A quick note on the two spiders available in the TAPP primary. The most common version is the button spider. A roller spider is available at an additional cost. Due to the extremely low friction of the roller version, it will run at 500-600 rpm lower than a button version on a sled tuned around the 300 hp level. Our preference is to use the button spider on sleds up to around the 350 hp level. We’ve found that the button spider works very well, runs quietly, and keeps the clutch closer to the center of the tuning window for the vast majority of sleds. For those wanting maximum performance at higher horsepower levels, the move to the roller spider is appropriate. We used the button spider on one of our demonstration sleds tuned to the 400 hp level for years with excellent results. On our 500+hp race sled, we use the roller spider.

A couple of more notes on friction and efficiency. Unnecessarily stiff springs and heavy weights in any clutch lead to more friction, more wear, and less efficiency than softer springs and weights. Stiff and heavy tuning components result in the clutch fighting itself and less energy is transferred to the sheaves and belt. For the highest performance and hp to the track, use the softest springs and lightest weights practical.

In the TAPP primary clutch, these efficiency considerations also come into play with the ramp. We mentioned in part 3, that the B side of the ramp will “pull harder” due to its flatter profile curve. That, and higher engagement, are the reasons why racers prefer the B side. The steeper the curve and angle the ramp, the more energy is lost in the clutch and less power is transferred. That is why steeper ramp angles run higher RPM. The clicker setting influences this as well.

Most tuners will prefer to set up their TAPP primary so that they most often run with the clickers in the 3 or 4 position. This gives them some tuning window to go up or down. However, setting the clicker in the 1 position lowers the outer edge of the ramp resulting in the flattest profile. For maximum efficiency and power transfer, racers may want to setup their clutch to run with the clickers on 1, adjusting the weight on their arms (reducing) if necessary to hit their desired RPM. Clickers on 1 will give the highest level of power transfer and performance. The trade-off is having a smaller quick-adjustment tuning window to work with.

Moving from the ramp to the rollers, there are performance considerations there as well. The most common setups use +1 or +2 rollers with a shorter bolt and fewer washers. This type of setup yields excellent long term durability with the majority of the weight centered in the shift arm directly on the ramp. However, larger diameter rollers change the relationship between the swing arm and the ramp, increasing the distance between the center of the roller bolt and the surface of the ramp. What we discovered on the dyno is that this increased distance led to decreased efficiencies in the clutch and less track horsepower. Increasing roller size (and associated weight) is an easy way to configure the shift arms. However, using smaller rollers and adjusting the weight of the arms with a longer bolt and washers to compensate, can yield higher performance in race applications where every little bit counts.

We discussed the springs in detail in part 1 of this series. To recap, trail riders will prefer the Blue spring with its lower engagement and smooth shifting characteristics. Racers will most often move to the Brown or Black spring, mostly to help raise engagement RPM so they can build more boost when using a 2 step or launch control function.

There are so many ways to setup your clutch that there is likely no “one best” combination. The best results will depend on the sled, track length and traction, sled modifications and desired riding style, snow conditions, etc. etc. etc.. The number of possible combinations is almost mind-boggling. Our hope is that you’ve found this series on the TAPP Primary Snowmobile clutch helpful in providing you with some more information on what is possible for optimizing the performance aspects that are most important to you.

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.

TAPP Snowmobile Clutch Tuning - Part 2 – The Shift Arms

The TAPP primary snowmobile clutch is closer to the SkiDoo TRA in its design concept than it is to a more common swing arm style like that of the Polaris, Yamaha, Arctic Cat, Comet, and others. However, a large part of the appeal of the TAPP clutch is that it is a 4-arm clutch which greatly increases the adjustability. This increase is because tuning changes can be made to pairs of arms (always across from each other to keep the clutch in balance) rather than having to make changes to all the arms in the clutch. This is a significant advantage when compared to a 3-arm clutch.

Back to the focus of this post, the shift arm. The shift arm swings or pivots on a pin at its base. At the tip, a bolt holds a roller in the center between the two sides of the arm. As RPM increases, the weight of the shift arm forces it out against the ramp. When the RPM is high enough, the arm climbs the engagement “hump” of the ramp and engages the belt.

The weight of the arm affects RPM and can be adjusted in three ways. First, different length roller bolts can be used in combination with washers under the head and nut of the bolt on the outside of the arms. The combinations of bolts, washers and heavy “race weight” washers yield a lot of adjustment in the arms. More weight on the arms makes them pull harder as they have more centrifugal force and lowers RPM, less weight shifts less aggressively and raises RPM. In effect, it’s like going to heavier or lighter weights in the more common style of clutches. The cover of the TAPP clutch must be removed to make roller bolt and washer adjustments to the shift arms.

The second way the weight of the arms can be adjusted is with different rollers. Different size rollers are available which weigh different amounts. There are the base rollers which weight 9.9 grams and plus size rollers as follows:
- Size +1 ( 16.5 mm ) – 12.5 G
- Size +2 ( 17.5 mm ) – 15.3 G
There are other considerations with respect to roller size, but we’ll save those for an advanced tuning tips post. Like the roller bolts, the cover of the clutch must be removed to make roller changes.

The third way the weight of the arms can be changed is through Allen screws inserted into the threaded holes in the ends of the arms. Inserting screws into the front side of the arms is easy and can be done without removing the cover from the clutch. As always, if screws are added always add them equally in opposing arms. Additionally, if only one screw is added per arm, say in the right side of the arm, be sure to add the screw to the opposing arm in the same location to keep the clutch in balance. Screws added to the front side of the arm will affect RPM lower in the shift curve. Screws added to the back side of the arm will affect RPM less at engagement and more equally throughout the shift curve.

So there is a lot of adjustability in the weight of the arms. How much does it make a difference? Each total gram of weight added to the arms makes about a 40 running rpm difference. I say total weight because you must always add or subtract weight in pairs of arms. For example, adding a washer (which weighs about 1.2 grams) behind the head of one bolt on a pair of arms adds 2.4 total grams of weight to the clutch. This total weight would make about a 100 rpm (2.4 x 40) difference (give or take). When adjusting engagement, heavier arms will have a lower engagement RPM than lighter weight configured arms.

In part 3 of this series, we’ll discuss the TAPP clutch ramps.

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.

We regret that circumstances have made it impossible for us to attend the largest stage in snowmobile drag racing this year, but we'd like to wish "Good Luck and Safe Racing" to everyone headed to North Branch for Hay Days Grass Drags. We wish we were there with you. You might see last year's heaviest sled/rider combo, and the event's biggest underdog, next year in 2027!

Trouble finding a spanner sized properly for the TAPP Secondary spring cover? We have you covered with our latest tool. The material won't scratch the anodized clutch finish and the pin is steel reinforced for strength. Introductory priced at just $19.00 CDN and shipped from Canada. On the website now: https://www.maxcelerationracing.com/product-page/tapp-secondary-clutch-spring-cap-spanner-tool

With our Thrust Claw Snow Drag Chisels now in stock and ready to ship, we introduce our newest combo - the Traumatizer! Making maximum use of the Hellevation Elevated Traction triple billet support plate, our steel base studs, and the new Thrust Claw chisels, this combo provides an unparalleled 2.25" of snow thrusting surface width. Mix a few into your pattern for maximum launch. Visit the website for full details at: https://www.maxcelerationracing.com/product-page/traumatizer-triple-claw-combo

Tech tip: Sidewinder Clutch Offset

There is a lot of information floating around with regard to Sidewinder clutch offset and belt life. In our experience, belt failures are usually a result of malfunctioning, poorly maintained, clutches or incorrect offset. This post is about offset.

An easy way to set offset on stock Yamaha clutches is to simply get the Hurricane Alignment Tool and away you go. If you want to get further into it or have aftermarket clutches, read on.

The diagram is from the Yamaha manuals and shows how the offset is measured. Notice the factory tolerance is wide at 3mm. That's probably too large a range. Our experience is that 59mm has worked well even at HIGH horsepower levels.

The measurement is different for aftermarket clutches as their measurements are different. For example, a TAPP primary clutch has the same inner sheave outer edge thickness as a OEM Sidewinder clutch (about 6mm). However, a TAPP secondary clutch has a thicker fixed sheave than the OEM Yamaha secondary (8mm vs 5.5mm). The thicker sheave has to be taken into account in the offset measurement as the measurement is taken from the outer edges of the sheaves. Additionally, any difference in the belt width must be accounted for as well. Wider belts and/or thicker sheaves mean increased offset measurement.

These measurements do NOT apply for Arctic Cat sleds with factory clutches. However, they can be used if using aftermarket clutches on your ZR9000/Thundercat. The 59mm offset is correct if the primary inner sheave thickness is 6mm, secondary outer sheave thickness is 5.5mm and the belt has a top width of 35.72mm (XS825). If your clutches or belt used have different measurements, adjust the 59mm spec accordingly. As an example, a TAPP primary and TAPP secondary with the XS827 belt should use an offset of 64mm.

This post might start a bunch of arguments, similar to which type of oil is best, but we are just sharing the information based on our experience and results. Hopefully it helps some of you out.