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February 2016 Ask the Experts

Answers to your tech questions about sleds, stud patterns, engines, clutches, fuel efficiency and more
snowmobile track stud pattern backers
Studs are more than numbers
Q:
I’m looking for stud quantity, size and pattern for a 2007 Arctic Cat F5? – Gramps

A: The stock track for that machine is a 15x128x1.0-inch track. So you’ll want at least a 1.08-in. stud length and a count of 102 as a minimum recommendation.

Tunnel protection should be standard on your sled, but it wouldn’t hurt to double check.

Recommended stud quantity, size and pattern will differ by the brand of traction product you choose and your personal preference/riding style. Some traction companies offer both a trail “safety” package and a “performance” package for the same sled. Regardless, you can find application guides for your sled on many of the major traction companies’ websites. Here are a few traction product websites to get you started:
- Experts
Reader Response: Ski-Doo vs. Polaris
Q: Just wondering if anybody used a TRA primary with a Polaris secondary and if there is any difference compared to Ski-Doo secondary.  – mach69x

A: The Polaris and Ski-Doo button helix secondaries are just about clones of each other. The real differences would be in the way you set them up for the primary. The TRA needs a lot more spring tension and different angles than a P85 primary would need. I’d say the change isn’t worth exploring because it would require a new jackshaft due to the different secondary shaft size. – chines
XCR 800 engine answers
Q:
On the XCR 800 crankshaft, do all three of the rod journal pins press out of the counterweight parts of the crankshaft? There used to be a company that made Pro-TI rods, titanium connecting rods. Is this company still around, or is there another that makes lighter and stronger rods? – cool storm

A: The crank should be a full pin style and titanium is cool but not necessary. If you want some crank upgrades, go with hybrid bearings or full ceramic, and just a better quality rod. – Todd Guthrie, Dyna-Tek Performance
2006 Ski-Doo Renegade 600 H.O.
Ski-Doo Comparo
Q: I want to upgrade from my ’02 MXZ 700 to a ’05 MXZ 600 SDI Renegade. How do you think they compare? – Anonymous

A: You’re talking about two different chassis and engines, so comparing the two is difficult. But since you asked … The 2005 MXZ Renegade marked the second year of the “rider-forward” REV chassis from Ski-Doo. You’ll sit more over the engine than the behind-the-engine feel of the ’02 MXZ built in the ZX-X chassis. Both engines are widely regarded as more than capable. We’d venture to guess you’ll find the larger 16x136x1.25-inch track on the Renegade even more to your liking on and off the trail than the 15x121x1.0 of the 2002 MXZ. However, the super-wide 47-inch ski stance of the Renegade may not be as friendly in boondocking situations as you’d like it to be. Over time, the OEMs discovered a narrow stance was actually better for off-trail maneuvers. But each rider has his or her own style/preference, so what we think may not always be exactly what you’re looking for! – Experts


600 SDI MPG
Q: I bought a used 2006 Ski-Doo Renegade 600 H.O. last year with about 4,000 miles on it, but in immaculate condition. It has only one problem: horrible gas mileage. It’s a consistent 10-12 mpg for groomed trail riding. I have ridden with several of these 2006 600 H.O. engines in the past, and they are very capable of 16-20 mpg. Where do I start looking? Is this a sensor problem, a fuel system problem, or an ECU problem? – Mikuni Madman

A: If it is a carbed version, there are several things that can be done. A lot of my customers have dropped one main jet size, and taken the plastic packing washer that is under the jet needle and put it on top of the clip that holds the needle. This improved performance and netted better fuel economy. You have to be careful to pay attention to the amount of ethanol in the fuel you’re using. When doing any carb recalibration, always check piston wash and plug color, and adjust jetting as needed.

The next option is changing your drive ratio. Many owners of that sled will drop a tooth size or two on the jackshaft. That will result in a transmission that works easier to maintain mid-range trail speeds and may actually be able to sustain your current top speed. Both of these simple modifications should get your machine running better and more efficiently. Always pay attention to belt condition, idler wheel bearing condition and track tension. – Todd Guthrie, Dyna-Tek Performance

Checking other MPG issues
There are a couple of things that should be checked, and could be culprits causing gas mileage to decrease. First thing that should be done is a leak down check on the engine. Reduced compression is one of the main culprits that can cause reduced gas mileage. Others include poor spark, plugged air intake, broken reed valve, or improper reed valve seal. The ECU will typically not cause any fuel mileage issues. – Jason Houle, Straightline Performance
1998 Polaris 600 RMX twin cam snowmobile
Clutch won't engage
Q:
I bought a ’98 Polaris 600 RMX twin cam. It’s been sitting for six years. I got it running, but I’m having issues with the clutch. It won’t kick in until about 7000-8000 rpm. I replaced the spring because it was broken. I put new weights on it and they are a slightly heavier 62 grams. I took apart the clutch and cleaned it, but it STILL didn’t kick in until about 7000-8000 rpm. Can anybody help me? – rmx600

A: If it is not engaging until 7000-8000 rpm, the drive clutch has a major problem. I’d assume it is binding on a bushing or has a bad roller. Since it is a 1998 model (17 years old), I’d pull both clutches off and go through them completely. You will most likely find multiple problems that are causing this issue.

On the drive clutch (the one hanging on the engine), you’ll first need to check both bushings in the moveable sheave, and the shaft needs to be inspected for rust or corrosion that would keep the bushing from sliding freely on it.

Second, check each of the rollers that the weights ride on to ensure they are moving freely and they have no flat spots on them. On a sled that has been sitting for a number of years like this, it is very common for rust or corrosion to develop on the shaft that the bushings ride on (both the main shaft that the moveable sheave bushings ride on as well as the pins that the rollers ride on).

Third, check for rust or corrosion between the weight bushing and the weight pin, which would lock the weight to the pin. Corrosion in any of these areas will keep the clutch from shifting until the centrifugal force is high enough to force the clutch to shift past this point. That would explain the 7000-8000 rpm engagement.

Finally, to verify that the moveable sheave will shift properly, pull the cap off of the clutch, remove the spring and then torque the cap back in place. Now run the clutch by hand through its full range of motion to see if there are any “sticky” spots in the shift. This way, you can tell if you have a tight bushing or an issue with your buttons. Once you ensure that the clutch shifts properly, reassemble it with the spring in it. The cap and spider both have an alignment “X” mark on them. Make sure and line the X’s up when reassembling it.

On the driven clutch, again I would check both bushings and check the shaft for corrosion. This sled has a button secondary on it, and the buttons and large diameter bushing that runs on the helix are the most common problems. The outside of the helix will have bushing material transferred onto it that will need to be cleaned off.

Also, if you look at the helix bushing and see the copper exposed, then it’s time to change the bushing (if it has many miles on it, it will be bad). Before putting it back together, make sure to polish the ramp area of the helix where the buttons ride. This will make the clutch shift much smoother.

The driven clutch will have no effect on your engagement rpm, but if you do these simple service items, it will shift much better than if you leave it alone. When you reassemble it, the clutch has to be wound past one ramp to preload the spring. Also, pay attention to the hole position the spring is in and put it back in the same place as before. This would also be a good time to replace the driven spring, as I’m sure it has lost tension over the years. We recommend replacing springs every couple of years. – Jerry Mathews, Starting Line Products
2015 Arctic Cat XF 9000 Limited trail upgrades
XF 9000 recommended trail upgrades
Q:
I recently bought a 2015 XF 9000 Limited and would like to change the sound of the motor without being too loud. I have also heard the tuners really bring the engine to life, but I don’t want to jeopardize reliability. What are your recommendations? – DirtyHarry

A: You’ve asked this question in the right issue of AmSnow! Our Tech Editor, Olav Aaen, has a full article detailing a couple of aftermarket tuners on pg. 44. There are many options to consider depending on budget, ease-of-use preferences and where a particular tuner might be most usable (in the shop vs. on the trail).

As far as upgrading your exhaust, there’s a multitude of options with legally acceptable decibel levels for trail riding. Most options will run $300-$450. What you end up with will depend on what’s most important to you. If weight savings is most important, you might consider a carbon fiber option such as the one from Straightline Performance, which saves 18 lbs. If noise level is less a concern, you could look at the Competition Series by Speedwerx, which saves 15 lbs. but is slightly louder and designed for competition use. Bikeman Performance has had plenty of success with its Full Velocity muffler, which offers a weight advantage of 9 lbs., a 13-14 hp gain and only 5-6 db more than stock.

Cosmetic concerns, such as sound and appearance, are only part of the equation for selecting exhaust items.

A lot will depend on what your desired performance benefits are, if you run any different fuel programs with the tuner, etc. Our best advice would be to get on the phone and talk to any of a multitude of aftermarket companies that work on turbo Cats to see what they’d recommend for your application. – Experts

More XF Mod Options
That is a very bulletproof engine in that sled. Any of the four stage ECU programs work great, and all need an aggressive clutch kit to complement the additional power. It’s a turbocharged engine, so you can use just about any aftermarket silencer and maintain good sound levels for trail riding, since the turbo chops up the sound all on its own. One of the best purchases is a four wheel axle kit, and make sure clutch alignment is on for belt longevity. This machine in stock form is a touch faster than the best 800s in the 2-stroke category. With the ECU reprogramming, it is unstoppable on the long straights. With some good suspension tuning, it can also be fun in the tight twisters. – Todd Guthrie, Dyna-Tek Performance
New Indy 800 motor?
Q:
I know that the new AXYS has a new version of the Cleanfire 800 motor that was not put into the 2015 Indy 800. Does anyone know what version of the 800 will be put in the new Indy 800? – 1000cc

A: Right now, our best guess is that the 2017 800 Indy will still have the former 800cc engine (not the new H.O. version), since the Indy still sits in the Pro-Ride chassis. The AXYS chassis and the 800 H.O. were developed by Polaris in tandem. The motor mounts and more are different. Unless something changes on the Pro-Ride chassis, the new H.O. engine simply isn’t going to fit correctly. With the success of the AXYS, it may not be worth the engineering investment to make that happen. – Experts
If you ask it, they will answer!
Each month, we take a sampling of questions from our “Ask the Experts” forum to showcase in the magazine. Our online forums allow users to ask questions and get them answered by some of the top minds in the industry, from ourselves and companies like Straightline Performance, Dyna-Tek Racing, Starting Line Products and more! All you need to do is log on and register your user name. Go ahead; it’s FREE!
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