Now that we have a couple of years under our belts with the new high performance four-stroke snowmobiles, one of the most profound differences that we didnâ€™t originally expect or anticipate was the major difference in break in period. The four cylinder RX-1, for example, really doesnâ€™t start to loosen up and break in for something like 1000 miles! Anyone who performed dyno testing of an RX-1 when fairly new and then again after 1000-1500 miles should be able to quantify this in terms of actual horsepower, but the fact is these new engines do require a much longer break in period and a more faithful procedure to dimensionally stabilize the internal parts (pistons and cylinders especially). During this time, the internal parts will wear and polish themselves to correct operating clearances, as well as reaching thermal stability.
While Yamaha actually indicates the RX-1 engine can be operated normally after 300 miles, the engine will continue to loosen up and work better during the first 1000 miles for sure, and even longer. Prolonged operation above 6000 RPM for the first 100 miles is discouraged, as is continuous operation at a single throttle position. This ceiling is raised to 8000 RPM during miles 100-300, where continuous operation above this engine speed is discouraged.