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Before you make a buying or leasing decision about anyone's snow vehicle (including one of ours), there are some things we at Snow Craft Industries, Inc. would like you to consider:

I. NO SNOW VEHICLE WILL CLIMB THE NORTH FACE OF MOUNT EVEREST - No matter What The Salesman Says!

All snow vehicles have performance limitations, and these limitations vary between various models and brands. As with most anything else, there are trade offs involved between various performance factors. What is important is that you determine what factors are critical in your particular application.

Some performance factors you will need to evaluate in the machines include:

1. Deep Powder Maneuverability
   This is probably the most critical factor in areas of the country such as the Rocky Mountains, where the snow tends to be "powdery." With low moisture content. A machine's ability to cross areas of deep powder snow, without sinking in and getting stuck, is often referred to as its "flotation." The primary (but not sole¹) factor in determining a machine's flotation and ability to cross deep powder snow is its track weight per square inch on the snow. This is determined by dividing the weight of the machine in pounds by the number of square inches of track in contact with the snow. It is widely believed that an ideal track weight for deep powder snow conditions is .5Olbs. per square inch, or less. A common trade-off for a reduced track weight is a cumbersome track width; this prevents the machine from maneuvering in tight locations (such as mountain trails, narrow bridges, or between trees). Other trade-offs, to attain a low track weight, include under-strength frame elements and underpowered drive train components.
   
   
2. Ease of Turning
   The primary factor that determines a snow vehicle's ability to turn is the steering mechanism. Ever since snow vehicles were first developed, attempts have frequently been made to get away from tracks, often in an attempt to improve steering. Unfortunately, for general snow applications, it has never worked. Skis and oversize wheels have frequently been used on the front of snow vehicles but these machines have universally failed to maneuver reliably in deep snow conditions.

   This leaves only tracked steering mechanisms to receive serious consideration. There are two basic ways in which fully tracked vehicles negotiate turns: first, by directing a steering track (or set of tracks) in the direction of the desired turn or, alternatively, by varying the relative speed at which fixed position tracks rotate.

   The first method is used in the majority of Tucker Sno-Cats. These machines employ four separate sets of tracks and operate in much the same fashion as a 4-wheel drive truck. All four tracks turn at the same speed, with both pair of tracks turning, to point in the desired direction of turn. The advantage of this type of steering is that it is simple to operate and is very efficient when turning. This efficiency is due to there being full power to all four tracks when turning, as opposed to only partial power to one track when turning with a 2-track system. The disadvantage to this type of steering is a very wide turning radius.

   TUCKER or other 4 track

   

   The primary advantage to the "Tucker" system of turning the front or steering tracks is its simplicity for infrequent or untrained snow vehicle operators to understand. It is also very efficient because all tracks are pulling at all times, even in a hard turn.

   The second method by which tracked vehicles turn is by varying the relative speed at which tracks on opposite sides of the vehicle turn. This method is utilized by the vast majority of snow vehicles. In this method, the turning effect is accomplished by powering the track on one side of the snow vehicle at a different speed that the track on the opposite side. When this is done, the front of the snow vehicle will turn towards the side where the track is rotating slower.

   

   This method of turning has the advantage of being the most efficient power-wise and is the most common found in snow vehicles today.

   The mechanisms most commonly used to accomplish this type of turn vary widely but fall into four groups:
   
   

   1. Track Brake. In this type of machine, a track is slowed by applying a brake - somewhere between the power supply and the track drive mechanism (usually a sprocket). This is the more inefficient of the three methods and sometimes results in "jerky" turns which may cause a snow vehicle to become stuck in deep snow conditions. It also causes excessive drive train wear.
      
      
   2. Track Clutch and Brake. In this type of machine, a track is slowed initially by disengaging a clutch - somewhere between the power supply and drive mechanism. This results in a gradual, smooth turn. If a more abrupt turn is required, a brake can also be applied to the track when the clutch has been engaged. The drawback to this system is that the vehicle may not turn as smoothly or as quickly as a hydrostatically driven system.
      
      
   3. Planetary Differential. This is the most common steering mechanism in transport (as opposed to grooming) snow vehicles. Basically, a planetary differential steers by changing the gear ration and power to one track or the other and thus changes the track speed. The method by which the gear ratio is initiated involves the use of a brake band around a brake drum on each side of the differential. The brake band constricts around the drum when the snow vehicle operator pulls back on one of the steering levers leading to a change in the gear ration driving one track.
      
      
   4. Hydrostatic Drive. A hydrostatic drive system typically uses two hydrostatic motors - one to drive each track. The power to drive these motors is supplied by hydrostatic pumps, which are in turn powered by the vehicle engine. Hydrostatically driven vehicles are unique in their maneuverability. Most can literally turn within their own radius by reversing one track while leaving the other running forward.

      

      Note: This turn could be completed with the machine sitting in one spot. The drawbacks to hydrostatically driven units (other than their high initial cost) lies in the lack of efficiency of power transmission from the engine to the tracks. This results in the need for a larger power plant. In addition, there is very little that is user-serviceable in the hydrostatic system in the event of a breakdown.
      
      

3. Power Adequate for Intended Use.

   Many of today's snow vehicles were designed to move tons of snow quickly in ski grooming operations. This type of power is frequently excessive for other operations. When evaluating the power of a snow vehicle, you must always take into account the entire drive system and its efficiency. Sometimes a unit with a 5 0 h.p. engine and a highly efficient planetary drive system will outperform a unit with a 100 h.p. engine and an inefficient hydrostatic drive system.

   If your particular application does not require the ease of maneuverability provided by the hydrostatic system, then the additional horsepower is wasted.

   A factor that is sometimes overlooked when evaluating the power of any given machine is the effect altitude will have on it. When you evaluate a machine's performance at 5,000' you must remember that the machine's power may be reduced by more than 30% when the machine is operated at 15,000'.

One of the most common untruths related to snow equipment is the statement, "Requires Virtually No Maintenance" or "Never Breaks Down." Even the most reliable machine requires regular preventive maintenance as well as adjustments and will still fall victim to an occasional mechanical breakdown. What is unique about snow vehicles as opposed to other machinery (such as cars, trucks, or tractors) is that many of the really well built ones don't have enough common sense to quit running when they are broken. One true story told at Snow Craft frequently deals with the "Monster Machine". If you have ever seen a late night movie where a monster refuses to lay down and die in spite of multiple gunshots, explosions, missing arms, etc., you'd know why we call this machine the "Monster".

This particular machine was a 1 5-year old snowcat that had not been used for many years. When we arrived it not only started but started immediately (which, by the way, terrified the mice who had built homes throughout the interior). In the process of a test drive, the Snow Craft mechanic proceeded to put the vehicle into third gear and without so much as a warm-up drive, climbed 1/2 mile up a 45¡ snow-covered hill. His only comment after the drive was, "This machine runs like it was just made!" When the machine arrived at the shop and had the accumulated mud, grease, rust, and snow washed off, the "just made" machine turned up to following problems:

• The machine had 5 axles, which had been welded to the frame. Only one axle was still welded to the frame; the rest had cracked loose over the years.
  
  
• The drive train rear end is designed to be bolted securely to the frame with six 1/2" bolts. It is widely felt that this connection is critical and any motion may cause immediate and severe drive train failures. The "Monster" had only 2 of the 6 bolts remaining and they were so loose that the rear end hung down almost 2" from its intended position.
  
  
• The drive axle housing, which extends from the drive train rear end to the drive sprockets, is subjected to exteme bending force by the operation of the vehicle. For this reason, it is designed to be fastened to the frame by eight l/2" bolts (four on each side). The "Monster" had 5 bolts remaining and 2 of those were finger-tight.

What you need to evaluate when considering the mechanical reliability of a machine is does this machine look like it is built to handle the abuse it undoubtedly will receive and keep running? Or, does it look like strength was sacrificed to keep weight and cost down? Better yet, call some past customers and inquire about the mechanical record of their machine and how helpful the dealer who was sold him the machine in handling any problems.

Remember also that the more complex a machine becomes, the more frequent and expensive become the breakdowns. A final point to consider under maintenance (and one that is often overlooked, sometimes with disastrous results) when evaluating a snow vehicle is the vehicle's:

CRITICAL APPLICATION RELIABILITY.

When a ski area purchases a snow vehicle (with few exceptions, most snow vehicles are designed for this intended user), the "go/no go"²reliability of a snow vehicle is often only a concern as it relates to the nuisance factor of and time lost because of a "no go" breakdown. In the case of a ski area, the driver of the "no go" snow vehicle merely puts on his jacket and uses his radio to call another snow vehicle for a ride to the bottom of the slope, while trained repair personnel at the ski area make the necessary repairs.

Put the same snowcat, with the same operator, in the same situation but this time place him four miles back in a remote region trying to locate a power line failure during a blizzard. The "no go" mechanical failure takes on an entirely different meaning.

Thus, "go/no go" reliability is an important factor in evaluating a snow vehicle that is intended for use in critical application service.

While the durability and strength of the components making up the snow vehicle in question are obviously of importance in making this determination, there are two other equally important factors:

1. Field Repairability.
   

   This refers to the user's ability to make repairs correcting "no go" breakdowns in the field, using only tools and parts carried on the vehicle.

2. Sudden Failure Factor.
   

   Briefly, this refers to the amount of warning that a failing part will give prior to a "no go" breakdown. An example of a potential "no go" breakdown giving ample advance warning of the problem would be the gradual wearing out the clutch surfaces in a drive train. The operator could be forewarned of the problem by either visually inspecting the clutch surfaces or the slow deterioration of the machine's performance due to clutch slippage.
   
   An example of a "no go" breakdown giving no advance warning would be the sudden, complete failure of a hydrostatic motor. These sometimes work beautifully, with no signs of difficulty, right up to the point that they stop working altogether, causing an abrupt"no go" failure.

   As with many other factors, you must evaluate the importance of a machine' s CRITICAL APPLICATION SUITABILITY in the context of your particular application.

FIELD VEHICLE EMERGENCIES

Field emergencies come in many different forms for the snow vehicle operator. Some of the most common types include:

LOSS OF STEERING CONTROL.  In all but hydrostatic drive machines, this is a fairly common breakdown. It occurs when the operator experiences a loss of all or most steering control to one or both tracks. The most common cause is a failure by the master or slave cylinder in the steering circuit. This, in turn, is most commonly caused by the failure of a seal or gasket within one of these cylinders. Another common cause is low fluid level or air bubbles in either the master or slave cylinder. Some other causes include a broken brake band inside the rear end (common in 1200A and 1400 Thiokol series machines) or a broken fulcrum lever on the outside of the rear end. It should be remembered that, in many of these steering failures, the vehicle can still be operated, even with turning in only one direction if there is adequate space to maneuver.

TOTAL LOSS OF POWER.  This problem, fortunately, is not common in the field; but, when it does occur, it is a major problem. Although the failure can occur anywhere in the drive train, we will only deal with engine failure here. This is because failures of the transmission or rear end tend to be easy to diagnose in the field (it sounds like lots of big metal pieces grinding together) and are usually impossible to repair in the field.

Engine failures in snow vehicles are sometimes caused by ice or contaminants in the fuel line plugging the fuel flow, usually at a filter or screen. These problems are relatively easy to diagnose by checking for fuel flow at the carburetor. Curing these problems is often as simple as blowing out the fuel filter or adding alcohol or other de-icer to your fuel. Sometimes, when ice is the problem, you can even solve it by just pouring boiling water over the part that contains the blockage - commonly, the fuel filter.

ELECTRICAL FAILURES.  Another common area for field failure is the electrical system. Although the possibility exists for complex and not field repairable electrical problems, these are rare. For every blown ignition coil, there are ten loose wire connections or severed or grounded wires. One of my favorite problems is loose wires on the back of the ignition switch. Think how stupid you'd feel after walking out 15 miles in deep snow and then have someone else wiggle the dash wires of your "disabled" snow vehicle and drive it home!

Another wiring-related problem involves the burning or wearing of insulation against exhaust components or sharp, unshielded metal edges. The end result of both of these problems is the same - an electrical short. Sometimes this short stops in the wire or wire pair in which it starts; on the other hand, sometimes the short is not confined and spreads to adjacent wiring and eventually ignites nearby combustible materials. This problem can be avoided if periodic checks are made to ensure that no ungrommeted metal edges or hot exhaust system metals are in close proximity to any exposed wiring. If you are in a snow vehicle when a short develops, the first thing to do is disconnect the battery, then put out the insulation fire.

TRACK FAILURE.  Track failure is not an uncommon cause for a snow machine breakdown. The common failures fall into two categories: track belt tear or loss of tracks. Although both of these problems are bad, the track belt tear is definitely worse. This is because both problems require you to reinstall the tracks; but, with the track tear, you must also patch them.

Many track tears and subsequent cases of track loss are caused by not checking the condition of the belts before each trip. The presence of small, horizontal tears across the track surface are a sure sign of trouble to come if not repaired. These cracks typically appear on the outer edge of the outermost track belt and progress across the belt. These tears should be spliced with an overlay splice when they are l/2" wide if circumstances prevent replacing the entire belt. If these same cracks appear on the innermost rubber belt on either side, the problem is much more severe because these two belts are the power belts. Any tears in these belts indicate the belts must be replaced before the machine is used again.

The other common cause of track failure is track loss. The problem is caused when the tracks, for some reason, lose the tension necessary to stay on while in use. The most common cause for this is the track-tensioning device being set too loose. All snow vehicle manuals specify how to check and adjust the tension on various models of snow vehicles. This is the single most important thing you can do to avoid track loss. If you are not sure as to track tension, err on the side of"too tight". It may cause some extra track and sprocket wear, but it is the single easiest thing you can do to prevent track loss.

Some experienced operators will intentionally over-tighten their tracks when they know they will be operating where they must make sharp turns on steep hills. They do this because it dramatically reduces the chance of track loss.

This pamphlet has presented a highly over-simplified view of snow vehicle operations. It is only designed to provide an introduction to the topics covered. Hopefully, it may be useful to you.

by Art Seely, Snow Operations Training Center, ©1999

1  Other factors include such things as grouser design, weight distribution, and power-to-weight ratio.

2  "Go/No Go" reliability simply refers to mechanical problems that will disable a snow vehicle until repaired versus problems that will not.

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