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Memo Gidley's Secrets of Speed
Break-in Procedure
The ROTAX is a bit different from other engine formats in the area of engine break-in. The beak-in procedure must happen on the track, under load, not on the kart stand or any other manner where the engine does not experience load conditions. It is common practice in some forms of motorsports to break in a fresh engine, whether new or rebuilt, on a stand, without dynamic load placed on the engine. This type of break-in technique must not be employed with the FR125 Max. The rapid rises in RPM made possible by operating without dynamic load is detrimental to the connecting rod bearings, especially the lower rod bearing. Improper or incomplete "bedding" of the piston ring with the cylinder walls will lead to piston seizure. Make sure the engine reaches proper operating temperature, covering radiator fins with tape, if necessary.
Break-in has to be done at the racetrack. Start with a pre-mix of 33:1 with synthetic oil for the first ten liters of fuel. Make sure to use a size of main jet that will create a richer air/fuel mixture than that prescribed for the conditions where you operate the engine (see calibration chart in the Operator's Manual). For the first 15 minutes run the engine up to a maximum 7,500-RPM. Follow this with another 15 minute session running the engine up to 9,500 RPM. It is important to vary the RPM during the break-in process. Open the accelerator fully until the engine reaches the RPM mentioned above, lift off the accelerator completely, let the RPM come down to 5,000 and accelerate again. Make sure that the coolant temperature reaches a minimum of 130° F (55° C). At cold ambient air temperatures, the radiator needs to get partly covered by tape.
There also seems to be some relationship between engine failure during break-in and cold ambient air temperature. ROTAX defines "cold" as less than 10°C or 50°F. In conditions such as this, the engine tends to run lean causing a hotter combustion cycle. The piston and ring heat up rather quickly while the cylinder is slow to warm due to the cold air temperature. With the close piston-to-cylinder clearances, this unequal expansion increases the risk of piston interference with the cylinder wall or even the entry of the ring into the exhaust port.
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