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In the last issue we installed a Starting Line Products (SLP) single pipe on a 2007 Arctic Cat M1000. We knew this single pipe exhaust system would achieve more peak horsepower at a higher rpm than stock, and in order to harness this newfound energy, we needed to do some clutch recalibration.
Dozens of books have been written on this subject because few things can affect the performance of a sled as much as clutching can. Stock sleds as well as modified sleds can gain performance over generic factory settings through careful clutching mastery.
In this article, we provide information on how to change the weights and the spring in the primary clutch, without removing the clutch from the snowmobile.
What's first?Before we get started with the "how-to," you need to make a decision on the replacement clutch weights and spring. To help answer some commonly asked questions, SLP provides a clutching chart along with its pipe installation instructions.
According to its chart, if you ride at 8,000-10,000 ft. altitude, the recommended clutch spring is SLP's black/yellow, and clutch weight is SLP's MTX 68g, with no rivets. If you choose to stay with OEM weights, use 4 grams lighter per weight than MTX. Therefore, you need 64g OEM weights. In the driven clutch, both the spring and helix remain stock.
Lets get down to the nitty gritty!
Step 1: Start off by removing the eight 3/8-in. bolts around the clutch cover. The cover is under spring tension, so the bolts must be backed out evenly. Make note of the alignment buttons because the cover is balanced with the clutch and needs to go back the same way.
Step 2: Once the cover is removed, the tension is off, and we can begin to remove the weights. Arctic Cat uses a setscrew on the weight. Before the setscrew can be backed out, it must be heated to soften the thread locker. If this process is skipped, the setscrews will not come out. We used an electric heat gun to avoid any open flame around the sled, it takes a moment longer than a torch, but gets the job done more safely. You also will notice a little smoke as a sign it's hot enough to remove the setscrews. A 2mm Allen wrench is needed here.
Step 3: Remove the nut on the pivot bolt, tap out the bolt, removing the weights from the clutch. A trick of the trade is to use a mechanic's magnet to hold the weight. Also remember since we just heated them, they are still hot!
Step 4: Before installing the new weights, we put them on a scale, weighing all four of them and marking on them their weight, the grams (in tenths), and then grinding the heavier ones to the lightest. We did this by taking a little off the side, and it provided nearly perfectly balanced weights.
Step 5: Time to install the new weights! Here again, use the magnet trick to hold the weights while installing the pivot bolts through the clutch and weight. Take note of an alignment mark on the pivot bolt head; use this to align with a corresponding indentation or divot in the center of the pivot bolt shaft for the setscrew to go into. Use Loctite 262 red thread locker on the setscrew. Start putting in the setscrew, making sure it goes into the indentation on the pivot bolt. Then tighten the setscrew and pivot bolts.
Step 6: Install the new spring and clutch cover and you're ready to go!
Arctic Cat weights retail for $16.95 to $21.95 each. The 2007 M1000 is a four-weight clutch, while the 2008 models are a three-weight clutch. On our M1000 SLP single pipe installation, we used SLP's MTX clutch weights, which retail for $66.64 for a package of two for the four-weight clutch. The three-weight clutch is $99.95 for a package of three. The spring retails for $20.95.
MTX weights are adjustable too by simply adding weight via rivets (up to 6g per weight). There are two different sets of steel rivets, one weighing 2g and the other 3g, and there's a set of aluminum rivets weighing 1g included. Using the outer hole in the MTX weight will have the most effect on peak rpm.
MTX weights have a slightly higher heel height than stock weights, which tightens up the belt sheave. Shims may be needed under the spider to adjust for proper belt sheave clearance. Too little belt sheave will result in belt squeal, or the sled trying to creep at idle. To best solve this, you will need four tools: a clutch puller, a clutch holding fixture, a spider nut tool and a spider tool. All are available in the SLP catalog for Arctic Cat and Polaris sleds that MTX weights can be used on. These tools retail for about $190 total.
Just a final FYI, your favorite dealer will have tools to pull/split the clutch if re-shimming is needed, but that's another "how-to" article altogether!
Thanks to product supplier Jerry Mathews at SLP, Idaho Falls, Idaho, 208-529-0244,
www.startinglineproducts.com. Also, thanks to clutching gurus Ron and Cory Williams at Team Work Motor Sports, Rigby, Idaho, 208-745-1926.