Putting the Squeeze On

Finding Answers on Swapping Out Tracks

December 2005 Feature Viewed 3360 time(s)
Remember the days when a 136-inch track was a long track and 1.5- or 1.75-inch lugs were incredibly deep?
You can't help but snicker when you think about how we all thought those were monster tracks back then . which wasn't even that long ago.
Now fast forward to today, where there are enough options available that you can just about find any length/height combo you're looking for. A good example of this is in the 700cc mountain sled story elsewhere in this issue. Just in the 700 class alone, there are 13 track options. That's why most snowmobilers these days are content with the length and height of the lugs on their stock sled.
What if you're still riding one of those 136-inchers and just can't pony up for a new sled these days but want to get a little more out of your old steed? Not every sled on the snow is a new one and there are plenty of older models out there that still have lots of good miles left in them. One option is to go to a longer/deeper track (if you have the motor to turn it).
Now this is not going to be a step-by-step story on how to swap out a track. Rather, we asked a handful of experts in the industry what sledders should keep in mind if they're even thinking of changing out the track on their snowmobile. We threw questions regarding tunnel and track clearance and air movement and drivers and angles and rotated chaincases at these experts, hoping they could give you an idea of what you're getting into if you want to go long and deep. There's a little theory mixedin with all the answers, as well as some personal opinions and recommendations from each of those we asked to help. We posed these same questions to all four of the major snowmobile manufacturers but only received a response from one-Arctic Cat-so we'll start with them.

Jason Howell,
engineer, Arctic Cat,

(ED-Howell provided us with this information before he left Arctic Cat to pursue other interests.)
A few years ago Arctic Cat was limited in this distance (between the track and tunnel) by the length of the chaincase. We could only rotate and move the open distance by the envelope between the drive and driven shafts. Today we have an open envelope, in a sense, due to the new ACT drive unit. This drive unit allows us to have as much room as we want, as there is no top/driven shaft to hinder the envelope.
Many factors are considered when altering this region of the snowmobile. A lot has to do with balance and feel of the snowmobile in relation to the track length, engine package and everything else that goes into that particular snowmobile.
Is there a "right" distance between the tunnel and track? Arctic Cat believes that it can be anything that it needs to be today with the ACT drive unit that we have. There are many factors that play into decisions like this: what engine, what track length, what's the balance of the snowmobile and a lot more when designing a chassis. Typically we like to refer to our so-called "Mtn. Bible" that we design to and that is Build Your Own Fire Breathing Mountain Climber, written by Steve Janes and published by Harris Publishing in 1995. Although Steve never highlighted this area of the snowmobile we feel that it is extremely important. I don't think that there is any effect of having too much room. The problem is, with a chaincase you are limited to the size of the envelope.
You don't want the track to touch either the side or the top of the tunnel but you want to keep enough room in between the two to allow as much snow and wind through as possible.  

Allen Mangum, owner, Timbersled Products, Sandpoint, ID,

The factories will say one thing and the custom sled builders will say something different when it comes to tunnel clearance. All the talk is about air movement and snow buildup inside the tunnel.
However, the first thing I look for on a factory sled, before I take it apart, is if the track has been rubbing the top of the tunnel. Most factory sleds do rub quite often. This happens when the sled wheelies or comes down on the back of the track, causing the track to lift off of the upper bogy wheels, which gives the track slack and then rubs the tunnel. Two areas where this rubbing happens most often are in the front of the tunnel, just above the drivers, and also between the upper wheels and the drivers. When these two surfaces touch, it is like pulling the brake. This robs a lot of power, makes your clutches backshift and then you lose track speed.
Air movement or air pressure will only rob power at high speeds and speed is not a mountain sled's specialty; so I wouldn't worry about that too much. It is the amount of snow that is trying to be forced through a tight spot that will cause a noticeable power loss. A little added clearance between the tunnel and track will cure all these problems. I would have to say an overall 1.75 to 2 inches of clearance between the tips of the track and tunnel is a good all-around amount of clearance to have.
There are several ways to get this amount of clearance. First, and the cheapest way, is to install a longer set of suspension drop brackets to lift the tunnel up off the track a little. This will cure the track rubbing problem, but it will not give you any more clearance over the top and in front of the drive wheels, which is where the snow becomes a problem.
To fix this problem you will need to drop and roll the drive axle and there are several different ways to do that. First, you could install a chaincase drop and roll kit that will lower both drive shaft and jack shaft. Second, you could install a longer or lengthened chaincase that will only drop and roll the drive shaft and will keep the jack shaft in the stock location. Third, you can install an aftermarket drive system that will roll the drive axle down and back and will also save some weight. 
The last and the most extreme way to get a lot of clearance is to install a deeper tunnel. A combination of both will give you so much clearance that snow and ice buildup will be a problem (up near the front of the tunnel where it goes around the drive axle), so you will need to use a cooling system that runs under the tunnel. This will keep the snow and ice from building up on the under side of the tunnel.
There are a lot of older sleds, like about a million, it seems, out there so if you want to put a 151- or 156-inch track on them, you're going to have to do what's been mentioned. If you go with a track with taller than 2-inch deep lugs, you're going to have to put a smaller driver on. You may even have to get an anti-ratchet driver, which means the (replacement) track will have to have clips.

Mike Cassidy, owner, Fabcraft, Florence, MT, www.fabcraft.com

I don't believe there is a magic number for clearance (between the tunnel and track). I like to see at least 1 inch and preferably 1.5 inches between the tips of the track and the closest point in the tunnel or bulkhead, but that depends on the track you have and what you will be doing with it.
There can be too much room in some snow conditions, like wet spring snow. Too much clearance and you will have a buildup of snow at the top of the tunnel and the front corner of the bulkhead, which can turn to ice. When that happens you may be packing around 2 to 15 lbs. of dead weight everywhere you go. When it does melt and fall down onto the track, you could have a major ice jam going out between the drivers and the front of the bulkhead, which has been known to bust drive axles. The track needs to be able to physically remove most of the wet or melted snow (melted from coolers) or you will just have lots of buildup.
You can definitely have too little room. If you have too little room you will have several things happen. Your track may rub the top of the tunnel when you speed up, unless you run the track very tight. Centrifugal force causes the track to expand away from the center of its path, which will allow a close fit track to rub the tunnel and that will scrub track speed, not to mention wear your tunnel, track and hifax. It also will create high air pressure in the front of the tunnel, which also scrubs track speed and bogs the motor down.
You need to find a nice balance between the two extremes.
Air movement is a big deal with the new high profile tracks. A track acts just like a squirrel cage fan that you find in your vehicle's heater. They both have fingers on them that drag air in and send it out the exit. The bigger the fingers, the more air and snow they will drag with them. The shorter tracks, which have 3/4-inch lugs, will not drag as much air or snow into the tunnel as a 2.5-inch track so clearance isn't as big of an issue. Punching holes in the track is popular right now and some OEMs are coming with them already punched out. This will help relieve some of the high air pressure, but it does little for snow evacuation, since the snow is being thrown out from the track.
The best analogy I know is, imagine taking a hair drier and turning it on. Now put your hand over the end and restrict the air flow. What happens? The motor starts to lose speed and it uses more current to run the motor. The same thing happens with a sled. Restrict the flow and you lose power and speed.
What are the best ways to achieve the ideal clearance between the track and tunnel? First you need to evaluate a few things so you can decide on a track that will best fit your needs. No matter what anyone says, there is no perfect track out there that will do everything. Bigger isn't always better. We now live in a world of specialty tracks that are designed to excel in certain conditions. Shorter lug tracks carry higher track speeds but don't get out of the hole in deep powder as quickly as taller lugs. Taller lugs carry slower top-end track speed, but get out of the hole faster and with less spinning in powder. When you have decided on what track you want then you can look at your needs for tunnel clearance to accommodate that track.
What do I want out of my sled?
A. Do I want lots of track speed for straight up high marking?
B. Do I want lots of flotation for boondocking at lower speeds?
C. Do I just want an all-around sled that I can ride in any conditions and have a good time with, even if I get beat at the extreme end of the spectrum once in a while?
D. Do I want to cornice jump?
E. Do I want to run the hillclimb circuit?
2. What kind of snow conditions do I ride in most often?
A. Deep, fluffy powder
B. Wind-blown, crusted snow
C. Wet, heavy snow
D. Icy, hard snow
3. How much time do I have to complete this project?
4. How good are my mechanical skills?
5. What is my budget?

After you have picked your track you will know how much clearance you will need. You may be able to get the clearance you need by just going to a different size driver, but most often you will need to roll your chaincase or go to a belt drive or gear drive to achieve the clearance you will need with the 2.25- or 2.5-inch tracks. Rolling the chaincase, belt drives and gear drives all do the same thing to different degrees. They give you more clearance in the tunnel and should reduce your angle of attack.
There are several vendors who have rolled chaincase kits for do-it-your-selfers and others that will do the work for you. Do your homework and call the vendors, don't just buy what your buddy says you need. He may have different riding styles and wants from his sled than what you do. All good reputable vendors should spend the time to go over their product with you and answer any questions you may have. They should not dictate to you what you need to do. They should give you options and suggestions that will help you make an informed decision. If they won't, then move on to someone who will. You're spending your hard-earned money so make sure you buy a product that will come with technical help if you need it, not just the sale of the product.
To determine how much clearance you need, find a way to measure the distance between the tunnel and the closest track paddle inside the tunnel. Now do the same thing between the front cooler on the bulkhead and the closest track paddle. That will tell you how much room you have at any point with the given setup you currently have. When you factor in the height change of the new track you should have at the very least a half-inch of clearance. If you don't have that much you should consider going to a smaller driver or rolling your chaincase. Personally, I would consider one inch a minimum for good powder performance.
Sam Nazzise, owner, Nazzise Racing & Repair, Riverton, UT,

There are a couple of things to find out before you swap out tracks. First, determine the existing driver size and second, the existing clearance between the top of the tunnel and the track lug. Try to measure the clearance in the two tightest spots (see illustration).
Keep in mind that on a lot of the older machines, the track tapers up toward the front of the sled. You can best see this when you're looking at it from the rear of the tunnel. It tapers up to the tightest spots. The average clearance on stock sleds is from 3/4 of an inch to one inch.
Determining what those clearance numbers are will help you decide your maximum lug height. Other determinations on what track you would like should include riding style, rider weight, the type of riding you like, to name a few.
There are situations where a stock 1.5-1.75-inch track already on the sled can be replaced by a 2-inch track without having to change anything, except maybe drop one driver size. Making that switch will help on the bottom end (0-30 mph track speed, not what your odometer says), but once you get to higher track speeds in soft snow, it will slow you down because it can't pull the snow in and out of the tunnel because you've tightened up the area to where the clearance between the track and tunnel might almost be touching up to one half-inch.
There are four options to look at if you want to add a deeper lug track. These are in order of the cost to the consumer as well as optimum performance.
First, change driver size. If you're adding a deeper lug track and you change the driver size, you will always be going to smaller drivers, never bigger ones. Of course, this changes gear ratios, but that's a story for another day. Ballpark cost for this is $250-300.
Second, milling the fins and/or removing the front heat exchanger. On some sleds the only option is to remove the front heat exchanger if you're going to a deeper lug track. In other situations you might be milling entire fins off in particular sections of the heat exchanger. Ballpark cost for this is $375-500.
Third, roll the chaincase. The general rule of thumb here is drop one inch and roll three inches, but that can vary per year, make and model of snowmobile. Rolling the chaincase provides more clearance and improves the approach angle of the track, which helps the sled get up on the snow better. Ballpark cost is $400-600.
Fourth, install a new tunnel. I recommend and use Van Amburg Enterprises because they can customize a tunnel for length, height, roll and approach angle. I like using Van Amburg because we share the same views and a lot of times he'll do mods to the tunnel at no extra cost. Ballpark cost is $1,500.
As for clearance, you can have too little, but in my opinion, you can't have too much. I like 1.5-2 inches of clearance at the tightest points. And usually, when you're installing an aftermarket tunnel, you have the ability to run a tub or a U-cooler, which will help keep the snow from freezing in the tunnel.
Any of the above choices obviously help you obtain better performance on older machines, say from 2000 or older, but you can still gain performance on newer equipment by using the same basic theories. Track/tunnel clearance is like an air pump. The tighter the area is, the harder it is to compress snow and air coming in and going out, thus robbing valuable horsepower that could be the difference between having to turn out halfway up the hill or sitting on the crest of the hill with a smile. 
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