The difference probably lies in the clutches.
Sometimes the best tuning practices for clutching are more than just running the proper weights or installing the right helix for your altitude. A lot of times clutch tuners forget that little things do affect clutch operation and ultimately their overall snowmobile performance and reliability. These little things are usually fairly easy and may not require a large investment, but simply just involve a little bit of time, attention and know-how.
Here are 10 simple practices to make sure your clutches are running at their full potential.
NEVER SPRAY ANY LUBRICANT OR CLEANER ON A CLUTCH
The aluminum that clutch faces are manufactured from is a fairly porous metal and any type of chemical whether it be a lubricant or a cleaning liquid is going to be absorbed into the clutch faces to some degree. The problem with this is when the clutches are used and get warm, the tiny pores will release the slippery material, creating belt slippage and poor performance. To prevent this, never lubricate or apply any solvent based liquids or cleaners to any part of the clutches. When cleaning or servicing clutches, the last step should always be washing them in hot soapy water and then rinsing so that what is left is a nice clean surface to provide maximum traction to the belt.
WASH BOTH THE CLUTCHES AND THE BELT IN HOT SOAPY WATER
Not only should the clutches be cleaned with hot soapy water, but the belt should as well. When belts are manufactured, they use mold release to help the belt come out of the mold easier. This mold release usually leaves a residue on the belt which can cause belt slippage. Cleaning the belt with a soft bristle brush in hot soapy water and then rinsing will reduce the chance of slippage with a new belt.
CHECK AND ADJUST FACTORY CENTER-TO-CENTER AND CLUTCH ALIGNMENT
Quite often clutch alignment or center-to-center measurements can vary from what the OEM specifies, even on a new unit. This can hinder clutch efficiency and cause pre-mature belt wear or failure. The factory service manual lists the measurement specifications for each model and the procedure for proper measurement. If one of these measurements is not correct, the motor mounts may need to be loosened so the motor can be arranged to bring these measurements back into specification. In some extreme cases, the motor mount plate or straps may need to be notched or slotted to allow enough movement to achieve proper alignment or center-to-center distance.
ADJUST FOR PROPER BELT-TO-SHEAVE CLEARANCE
Belt-to-sheave clearance is the amount of side-to-side free play that the belt has in the primary clutch. If this free play is excessive, the machine can experience a number of negative side effects such as an overly abrupt engagement, an engagement bog, a low speed hesitation and even premature or excessive belt and clutch wear.
To prevent these effects, check and adjust the free play so that the belt has .010-.020 inches clearance between it and the clutch. It is best to take this measurement using a new belt and get the clearance as close to .010 inches as possible to allow for belt wear. To get an accurate measurement, pull the belt tight around the center shaft of the primary clutch while sliding it to one side against the sheave so that the gap is all on one side of the belt. Use a feeler gauge to measure the open gap between the belt and the clutch sheave. If the clearance is not within the specification, the spider will need to be disassembled to allow access to the shims that will need to be added or removed to correct the issue. Consult the service manual for spider removal procedure or contact a performance shop or dealer that offers this service.
MAINTAINING WEAR ITEMS CAN SAVE YOU TIME AND MONEY IN THE LONG RUN
The belt is the easiest wear item to replace and often needs it soon before it fails. A worn belt can cause a significant loss in performance, yet we often forget to install a new belt as our first troubleshooting test, costing us time and even money if a destroyed belt damages other parts. The belts that are being used on new, high horsepower machines are so strong that they will wear to the point of poor performance yet not de-laminate or fray for some time after.
Other wear items often overlooked are bushings. All bushings including cam arm (primary weight), cap, sheave and helix bushings should be replaced when the free play gets close to or exceeds its allowable amount. These specifications can be obtained from the proper repair manual or your local dealer. If these types of serviceable parts are ignored, the wear will reach the point of eating away at the actual clutch, making the entire clutch non-serviceable and in need of total replacement. A $5 weight bushing is much easier and cheaper to replace than an entire $400 to $1,200 clutch assembly.
Fuel economy is also reduced when clutches aren't working to their full potential. To achieve the best fuel economy, all parts need to be in good shape, and if they are not, horsepower will be wasted trying to make the worn part do its job. Any time horsepower is wasted, fuel economy is reduced and cost of operation is increased.
USE THE SPECIFIC BELT RECOMMENDED FOR YOUR CLUTCH SETUP
What brand of belt should I use? This is a fairly opinionated question and often the answer lies within the person who designed, developed and is specifying the clutch components that are being used. Starting Line Products typically uses the OEM belt recommended for each individual sled because that is what most customers will be using. Each sled at one point had the OEM belt (from the factory) and most customers just simply replace it with the same belt. The key here is not what brand of belt is being used, but that the owner continues to use the same belt as was originally designed for whatever clutch components are installed in order to maintain consistent performance and reliability. Each brand of belt will act differently on a given unit because of differences between belt designs. Snowmobiles can vary as much as 200 rpm just from changing to a different brand belt. Therefore, if you decide to change to a different style or brand of belt, some re-tuning may be required for optimum performance and efficiency.
UPDATE CLUTCH COMPONENTS FOR DIFFERENT RIDER WEIGHTS OR TRACK SIZES
It is very common to see riders go to a bigger or more aggressive track. When extra traction or track weight is added, it puts more load on the engine, causing the peak rpm to drop, which can decrease track speed and performance. When this happens the rider needs to compensate by dropping a couple of grams of clutch weight in the primary clutch or reducing the chaincase gear ratio by gearing down or even installing a lower angle helix and/or possibly a stiffer spring.
The same basic rule applies for a rider who weighs more than the sled was originally calibrated for. The heavier the rider, the more load on the motor. Most clutch setups are designed with the average-sized person in mind, which would be anywhere from 170 to 220 lbs. If a rider weighs more or less than this, adjustments may need to be made to achieve full performance.
Another thing that affects clutching is adding more horsepower via aftermarket parts. In most cases, if more horsepower is being added, some clutch changes will be required to take full advantage of the extra horsepower.
BALANCE YOUR CLUTCH
Most OEMs have a range of tolerance for clutch balance. In other words, the clutch may not be perfectly balanced. Because of mass production and the sheer number that has to be manufactured, it is almost impossible for the factory to be perfectly accurate when it comes to balance. As time goes on, and clutches wear, balance is compromised even more. A clutch that is out of balance will cause vibration that can be very damaging to chassis, engine and clutch components.
Vibration also causes a dramatic increase in crankshaft wear and if bad enough, it will ruin a crankshaft in a very short amount of time. Clutch balance should be checked at least once a year and typically it is easiest to check it before the first ride of the season when routine pre-season inspection and maintenance is performed. This even includes a brand new unit straight out of the crate. There are a number of aftermarket shops and dealers that offer a clutch balancing service. A well-balanced clutch will transfer more power to the ground than one that is not.
DON'T OVERLOOK THE SIMPLE STUFF
There are a few other things that often get overlooked during routine maintenance. Of course all the bushings, rollers and pins should be inspected for wear, excessive free play and the sheaves should be inspected for signs of cracking or breakage. The entire clutch should be looked over for marks where the clutch has been impacted or damaged in a way that the integrity of the clutch could be compromised.
Clutch faces should have any black belt residue removed by cleaning with a scotch bright pad, steel wool or 320 grit sandpaper. They should also be inspected very meticulously for small cracks or heat damage. If cracks or impact damage are detected, the clutch should be replaced as this type of damage can result in a clutch exploding at high rpm, throwing shrapnel inside the engine compartment and damaging other parts. Inspect the PTO end for roughness and the taper inside the clutch for roughness. Repairs can be made with emery cloth or a taper reamer.
Maintenance schedules will vary depending on how the sled is ridden. A mountain sled should have the clutches checked and cleaned about every 500-1000 miles. Trail sleds can go longer and may need to be checked every 1000-2000 miles. Race sleds should be checked and cleaned as often as every race. At the very least, clutches should be checked and cleaned once a year.
CHECK YOUR SLED BRIEFLY BEFORE EVERY RIDE
Here is a list of small, simple things to check before each ride. It can be done at the time you lift the hood to fill the oil, preferably before you leave the house just in case you find a problem. Most of these problems will have a negative effect on clutch performance.
Belt deflection: Belt deflection is the amount of free play in the belt between the two clutches and it changes as the belt wears. It should be checked and adjusted (if necessary) every ride. Because of small variations from belt to belt, deflection should also be checked when a new belt is installed. Belt deflection specifications can be obtained from your dealer or service manual.
Belt condition: Make sure the belt does not show any de-lamination, fraying or wear spots. If it does, it should be replaced with a new belt and not another used one. Always keep two good belts on the sled. The spare should always be a new belt. It doesn't do any good to have a spare belt if it is used and may not get you back to the truck or may hinder the performance of the sled for the remainder of the ride.
Check the chaincase oil: this is a quick and easy thing that needs to be made into a habit. Check and adjust the chain tension. Make sure the oil is clean, and if it is dirty or milky, it should be changed. Make sure there are no metal flakes in the oil. If there are, pull the chaincase cover and inspect for worn gears, chain tensioner, drive chain or bearings.
Inspect the overall chassis and engine compartment: I have caught several problems before rides by doing this. This includes things like broken motor mounts, a track that is out of adjustment, loose bolts in the steering, bad bearings and so forth: problems that no one wants to deal with while riding.
As you can see, having a service manual for your specific snowmobile greatly increases the owner's ability to perform most of these tasks as well as provides a wealth of answers to questions that may arise during the ownership of a machine.
The dealer is a great source for information or services as well and should also be consulted for help with specifications or service needs. Implementing the practices listed above will maximize your machine's performance and reliability and most of all, it will help you to get the most enjoyment out of your snowmobile.