Why Are the Pistons Melted on a Snowmobile?

Enjoying a snowmobile with extra torque or pushing the performance limits always comes at a cost. Sometimes that price manifests in the engine. A common failure point tends to be snowmobile pistons.

  1. Heat and Pistons

    • Like most combustion engines, snowmobile engines require a heat source to create power and move. When this combustion heat reaches sufficient temperatures it can reach above the melting point of some kinds of metal. In a bid to reduce weight and dissipate heat faster, many small engines (like those used in snowmobiles) use lighter metals such as aluminum or aluminum alloy. Unfortunately, these parts are then prone to failure as engine temperature reaches above their low melting points (aluminum, for example, begins to melt at 400 degrees Fahrenheit).

    Running Lean

    • If a snowmobile engine runs correctly, there is a proper balance between fuel, oxygen and lubrication (oil). Too much oil and fuel with too little air floods the engine. Alternatively, too little oil and a lot of air raises temperatures, creating a condition called "running lean." When the snowmobile engine runs lean, temperature skyrockets due to increased friction and insufficient heat dissipation. The heat points with the highest temperature tend to occur near the spark plug and on the side with the exhaust vent in the piston cylinder wall.

    Ignition Timing Off

    • Ignition timing can be another problem and cause of melting pistons. Snowmobile pistons are driven by a crankshaft connected to a flywheel. The flywheel generates electricity, which also charges the ignition. The ignition sends a spark to the spark plug, which creates a flammable point to mix with the air and fuel as it compresses against the spark via the piston. If the timing is off, the combustion can happen too early or too late. When too early, the piston takes the brunt of the blast and heats up faster than it can dissipate. The result tends to be a melting point on the top of the piston about where the spark plug is located. Many times the damage melts a hole right through the piston face itself.

    Over-Revving the Engine

    • Torque and over-revving of a snowmobile engine can also contribute to high heat and over-working the parts. It's just like a person lifting too much weight for too long; at some point a muscle will pull or tear. The engine, when pushed beyond capacity, begins to heat up, again causing problems with the piston since it is made of softer metal than the rest of the engine parts. This problem frequently manifests with an engine that races too fast, even when in idle. The cause can be owner-error or mechanical, such as an air leak.

    High Combustion Fuels

    • For the snowmobile racer types, fuels with higher octane represent a temptation. However, if the timing, cylinder head compression and type of spark are not adjusted, the higher octane fuel will cause problems. Higher octane fuel requires hotter temperatures to combust. Low-idle situations won't be a problem, but upper-range rotational speed without adjustments can cause temperatures to boost beyond control. Again, the piston ends up melting and seizing into the cylinder due to heat and friction.