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A Mystery Unraveled

Neely Lays Down the Spin on Clutching

Published online: Jan 03, 2006 Feature
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   One of the great mysteries of snowmobiling is clutching. Clutching even borders on taboo for some sledders. They would rather ride an underperforming sled than mess around with the clutching. Or they would rather pay someone else to work on it.

Part of the mystery surrounding clutching is what some might consider the intangibles. Clutching is affected by riding style, rider weight and snow conditions. Clutching is also affected by jetting, gearing, engine size and track size. Even something as simple as belt wear can influence clutch performance.

The basics of clutching are easy enough, but those spinners can get complex. We asked Gary Neely, owner of Bucky's Outdoors Polaris (307-367-4561) in Pinedale, WY, to break it down for us and explain at least the basic things any sledder can do to his clutches if the sled is losing rpm. Neely has worked on clutching for dozens of years and for all kinds of riding applications-from hillclimbing and backcountry riding to drags to trail riding and racing. He definitely knows his way around the spinners.

One of the first points Neely made about clutching is that if you're going to tear your clutch apart, it's probably not a bad idea to practice at home before you try it on the snow. At the very least, make sure you know your way around both the primary and secondary so you're not left scratching your head when you get on the snow with clutch parts spread across your seat. More time wrenching usually means less time riding.


Maintenance Is Key

The more familiar you are with your sled's clutches, the more able you should be to spot any potential problems. "Maintenance," Neely said, "is a key component of keeping your clutches in good condition. Components are always wearing, but it's slowly, so sometimes you don't notice it (the wear). The wear happens slowly enough sometimes that your sled might lose 200 rpm and then you're not at peak rpm."

If this 200 rpm loss happens, don't assume that something major is wrong with your primary or secondary or both. Neely said, "You need to have your clutch cleaned and inspected to see what is worn. It may just need to be cleaned if it's a 200 rpm loss."

Or the trouble might be with the belt. Neely suggests that if your sled is losing 200 rpm change the belt first to see if that corrects the problem.

"However," he said, "8 or 9 times out of 10, it is wear and you may need to replace the bushings or something similar."

So if cleaning or changing the belt doesn't work, then a visual inspection would be the next step. Make sure your components are in good condition. Look at the internal bushings. Are they in good shape? Are the rollers flat? Are the weights worn? Take care of those issues first before you ever start trying to tune the clutches. Neely pointed out, "Your tuning won't work because you're tuning around worn components."

The components in clutches with 500 or 600 or fewer miles should still be in good condition. If the mileage is over that, then you should do a visual inspection. Caring for and doing this visual inspection is especially important for mountain riders, Neely said. "Wear is accelerated on a mountain sled versus a touring sled because riders are always on the throttle and climbing and pushing powder," he said. "That kind of riding is harder on a clutch than average riding. Another thing that accelerates wear is the bigger motors and bigger tracks these days. The clutch technology isn't quite keeping up with the bigger sleds and horsepower."

It's just common sense to pay attention and catch any issues early on because it can cost less to repair.


Looking It Over

The best way to do a visual inspection is to pry the primary open and turn the rollers. Something to look at, in addition to what's already been mentioned, are the sides of the rollers. If a little thread is showing on either side of the roller it's an indication the bushing is starting to go, even though it feels good.

It might be best to inspect your clutches at home, before you hit the snow so potential problems can be taken care of before your trip. Remember, more time wrenching on the snow usually means less time riding.

The next step is to determine if you need to tune or make a change. That might come after your visual inspection or maybe later while riding. Before you make a change, decide what your goal in tuning is. For example, Neely said, are you going to be drag racing? Hillclimbing? Speed runs? Trail riding?

You need to make this determination because of the different shifting patters you'll be going for with each kind of riding.


Establish A Baseline

Once that determination has been made, you need to know the peak operating rpm of your engine and make a baseline.

Neely suggests making at least three runs to make sure the sled reacts the same each time. If you're going to tune for trail riding, you can use a road. Or find a hill to test on if your preferred method of riding is hillclimbing and boondocking.

"We'll use the tachometer and speedometer in the tuning process," Neely explained. "When we're setting the baseline, we'll get an engagement rpm and full throttle rpm and also get a track speed off the speedometer at full throttle. It's a lot nicer to tune with a digital speedometer because they are usually more accurate."

One of the most important pieces of equipment Neely takes along on his rides, especially if and when clutch tuning, is a notebook. He uses the notebook for keeping track of the setups he tries as he aims for peak rpm. He showed us his notebook and the detailed notes from lots of runs, including information on snow conditions and what kind of day it was. With the notes he creates a spreadsheet which includes what's in the primary clutch, what is in the secondary clutch, what the rpms and speeds were as well as snow conditions and air temp. Of course, most average riders won't take the kind of in-depth notes Neely does, but if you're interested in reaching peak rpm, setup information is virtually invaluable.

Once you've established the baseline after your test runs, you can better determine what the problem might be if your peak rpm starts falling off. Clutching that is spot on allows the rider to run his sled at peak rpm while on the throttle. Your sled should still maintain peak rpm even when you hit a hill on full throttle.


What's The Problem

If the sled loses peak rpm when you hit the hill, the clutch is not backshifting well. Or if when you hit the hill it over revs at peak rpm, it's backshifting too much. It could also be backshifting too much if, when you hit the hill, you're trenching instead of pulling and the engine sounds like its revving and not pulling.

If this happens it's time to make one run to determine what you need to change, again using information from your baseline.

Once you've got the information you're looking for, then you have to determine whether you're going to make changes to the drive or driven clutch. One thing that will help you make the decision is to remember that the primary is the rpm sensing clutch (it feels what you're doing with the throttle) and the secondary is the torque sensing clutch (it feels the load the track is giving it). It's on the flats-before you hit the hill-that you can see (and feel) what the primary clutch is doing. When you hit the hill is when you can sense what the secondary clutch is doing.

Here's an example. If the engine is supposed to have a peak rpm of 8000 and you're tach reads 7800 or lower at full throttle, then you need to go after the weights and/or possibly the spring in the primary. If you're running lower than 7800 rpm, you need to put lighter weights in. Say the sled comes with 60 gram weights and the tach reads 7800-a loss of 200 rpm. Start with 58 gram weights (weights usually come in 2 gram increments). If it reads 7400, start with 56 gram weights.

If you know the baseline for your sled you can go to your dealer and get some components. If your sled is within 200 rpm of peak rpm, you may only need one or two sets of weights. If it is lower than that, maybe three or four sets.


Lighter Means More

Remember, lighter weights mean more rpm, heavier weights less rpm. Also, stiffer springs always means more rpm, softer springs less rpm. This is true for either clutch.

Put the weights in and then test the sled. Make changes until you get back to peak rpm. Neely said these kinds of clutch changes usually last about 1,000 miles.

"The big key to good tuning is to change one component at a time-never two," Neely said. "Then make a note of the change. That way you'll always know what it was you did that made the difference."

If you determine the change needs to be made in the secondary, which is getting all the input from the track, you'll most likely be tuning for backshift. Of course, when making your test runs, you have to have a hill where your clutch has time to shift. Meanwhile you're watching the tach and speedometer (pay attention to your surroundings while looking at your gauges-you don't want to be hitting a tree or something).

Say your speedo is reading 40 mph and the tach 7800 rpm. "So we know it's not quite backshifting well enough," Neely said. "That's where we get into the helix."

Most new clutches have a dual angle helix. The first angle is the "holeshot," or initial acceleration angle, while the second angle is the backshifting angle. These angle numbers are usually engraved on the helix. There is also a third number, which represents the "duration." Duration is how long it's going to stay in the first angle. If it's a long duration, then it's better suited to drags or speed runs. A shorter duration is for quick backshifting, which is great for mountain climbing.

Neely said, "Don't think the tuning is in the duration, though, as the duration is fairly standard." Also, the bigger the angle is the quicker it will go into high gear, the smaller the angle it is the better it will backshift.


Improving Backshift

Again, using 8000 as the baseline rpm, if you're at 7800 on the hill you're going to drop the second angle back to 38 or 36 in order to improve the backshifting to hold 8000 rpm (assuming the second angle was 40 degrees).

So make the change and then make another run.

Getting to the helix can be work, though. For the initial change out of the torques head screws you'll need an impact driver and a hammer and possibly heat to break them loose because they have locktite on them. The initial change-out should be done in the shop. After the initial change-out, you'll be able to use a regular T-wrench.

Say you change the helix and get the backshifting pattern you want but still are looking for another 100 rpm all the way through. That's when you need to look at changing the spring. If you're looking to change the spring, remember a stiffer spring will increase the entire shifting pattern from acceleration to backshifting. Stiffer means more rpm, softer is less.

You can take a couple of helix with you into the field but to change the spring you probably have to do that in the shop.

Watching the gauges is an important part of tuning either the primary or secondary. Seat of the pants might work or it might not. You might have two setups that feel good in the seat of the pants but then you look at the speedometer and one might be 40 mph and one 42 mph. Watching your gauges and taking even minor notes will go a long way in helping you get back to and maintaining peak rpm.

You don't have to be a Sherlock Holmes to unlock the mysteries of clutching. But you do have to pay attention to details and find out what works best for your sled. Even if your buddy has the same machine as you do, his setup might not work on your machine. That's because of all the variables involved in sledding-rider weight, track size, jetting and the like all have a bearing on your clutching. As with anything, practice and you'll get better. And if you really just don't like the wrenching thing, then contact someone-like Neely-who has been doing this sort of thing for years. There are plenty of clutching experts in the West, as well as across the snowbelt.