Chapter 15

The Mechanical Equipment Center (MEC) issues snowmobiles. You must attend a mandatory snowmobile/skidoo maintenance course at the MEC before your field deployment.

15.1 Snowmobiles in the MEC Inventory

All snowmobiles have two-stroke engines that require Mogas fuel pre-mixed with a lubricating oil. The mixture is 50:1 (12 ounces of oil to 5 gallons of Mogas). Average fuel consumption when pulling a loaded (1,000 pounds) Nansen sled is approximately 7 miles per gallon.

Park skidoos facing into the prevailing wind and always cover them. This helps avoid getting snow in the points and accumulating snow under the snowmobile's cowling.

15.2 Snowmobile Troubleshooting

15.2a Fuel Flow Problems

Symptoms: Engine cranks but won't run, no fuel present in line from pump to carb. Engine may run briefly after priming.

Diagnosis and Cure:

  1. Check fuel level in tank.
  2. Pry fuel line off carb, pressurize the fuel tank (seal and blow into the vent line) to see if fuel flows out of the end of fuel line. Crank engine and see if fuel pulses out of the end of the fuel line.
  3. If fuel flows and then pumps OK, the problem was probably just small ice crystals in the fuel pump valves. Pressurizing the tank dislodged them, thus solving the problem. Replace the line and go.
  4. If fuel flows when pressurized but does not pump, the problem is fuel-pump-related. First disconnect the vacuum pulsation line from the center of the fuel pump to the engine crankcase. Blow through the line -- if blocked, clean ice out of the line with a wire. Check the nipples on the pump and crankcase for obstructions. If the vacuum line is clear but fuel still does not pump, replace the pump or remove it and let it thaw.
  5. If fuel will neither pump or flow, then either the fuel line or the fuel filter is clogged. Clean the fuel line or replace the filter.
  6. If the tank is under vacuum when you open the filler, check the vent line for obstructions or pinches. Occasionally the line will rub against the exhaust, melting the vent hose. Make sure the tank is venting properly.
  7. If all of the above steps have been tried and still no fuel flows, check the fuel line for cracks or holes, and look for any obvious fuel leaks (i.e., discolored snow) in the engine compartment. Repair or replace the fuel line.
  8. A mixture of 30 mL of isopropyl alcohol per 5 gallons of pre-mixed Mogas will lessen the chance of water contamination and fuel icing.
  9. Pouring fuel through a trail flag or rag placed over a funnel will help eliminate any snow contamination of the tank and will filter the fuel.
15.2b Starter and/or Cranking Problems

Symptoms: Engine cranks slowly or not at all when key is turned.

Diagnosis and Cure:

  1. Usually this problem indicates a dead battery, and requires pull-starting the engine. The battery can be charged with an A.C. charger; however, it should charge on its own with skidoo usage, unless the battery is shorted or the rectifier is faulty.
  2. If the battery is fine, check the in-line fuse (30 amp) in the red wire near the starter, or see if the red-green wire has slipped off the terminal on the starter solenoid. Finally, the starter itself may be faulty.
  3. The recoil (pull) starter should be used when the engine is cold, so the electric starter is not overtaxed.
15.2c Spark Problems

Symptoms: Engine cranks but won't start. Fuel is present in the line between fuel tank and carb.

Diagnosis and Cure:

Unhook both spark plugs, push the spare plugs in the wire caps, ground the metal plug bodies to the metal engine housing, and crank the engine. If a spark can be seen at the electrode of the spare plugs, the problem may be that the installed plugs were fouled with excessive fuel, ice, or a piece of carbon. Install new plugs or clean the existing ones. When the engine is cold, the spark may be hard to see in direct sunlight.

Caution: Do not remove spark plugs for this test. If you have a spark and the crankcase is full of fuel, a fire could start.

If a spark is not present, the problem is in the electrical system rather than spark plugs. First, check the kill switches and all electrical connectors. If they check out OK, the solution of the problem depends on the engine type.

640 cc Engine: Problem is probably ice in the points (this mostly occurs after exposure to blowing snow). Remove rewind starter and starter pulley, rotate magneto housing until upper point set is visible, spray with alcohol, scrape with file, spray with WD-40, repeat for lower point set, and reassemble.

503 cc Engine: Electronic ignition -- problem is probably the igniter box. Replace.

Either engine: Still no spark -- may be a bad coil or a shorted wire.

15.2d Power Problems

Symptoms: Runs but lacks power.

Diagnosis and Cure:

If the engine seems to be running fine, but the skidoo has trouble with uphill starts, the problem may be with the clutch-driven pulley. Remove the cowling and see where the belt is riding on the pulley. The belt should be along the outer edge of the driven pulley when the skidoo is at rest.

If the belt is instead slotted down between the driven pulley halves, lubricate the driven pulley shaft, taking care not to lubricate the pulley faces, shift transmission into neutral, and alternately rev engine and apply brake until the belt works its way to the outer edge.

If the engine has very low power or dies when revved, remove the carb and check for ice. If ice is present, thaw out carb and reinstall. If the engine is weak and running rough, but the carb is ice-free, the problem may be a bad spark in one cylinder. Follow the procedures outlined above for cleaning/replacing spark plugs.

Altitude Adjustment: Assess mixture by hill climbing performance and spark plug color. Chocolate brown is correct; gray or white is too lean, while black is too rich. From sea level to 4,000 feet decrease the jet size by one increment from standard setting (i.e., 290 to 280):

At 4,000 feet to 6,000 feet decrease by two increments.

At 8,000 to 11,000 feet decrease by four increments.

Remember to richen up the mixture when returning to lower altitudes, under penalty of blown-up engines.

15.2e Track/Suspension Problems

Symptoms: Machine pulls to one side.

Diagnosis and Cure:

Check for loose or broken bogie sets.

Each operator should be made responsible for checking their machine before use.

Keep an eye on the track's adjustment. Keep the track centered between link plates. Watch track tension -- there should be a distance of 1-3/4" (this equals 2nd two joints of your 3rd finger) from track above bogies to frame edge below forward end of rail.

Beware of loose trailing straps and ropes; they can get entangled in the tracks and around axles.

Be kind to transmissions and shift gently. If gear(s) will not engage, turn off motor, shift gears and restart. Abusive shifting can cause drive train problems that are not repairable in the field. Never shift the transmission unless the snowmobile is stopped.

Note: LC-130 transport can result in skidoo damage either from abuse or during loading. Supervise the loading and inspect your machines as much as possible.

Many thanks to Dr. Bill McIntosh for his invaluable input.

On to Chapter 16: Sea Ice