Rotax 503 fan belt adjustment, adjusting the fan belt on the Rotax  503 aircraft engines.

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Adjusting the Rotax Aircraft Engine Fan belt.

One of the most neglected areas of the Rotax aircraft engine is the adjustment of the fan belt. One reason is that it is difficult to get at in most installations - thus it is ignored in preflight.

A simple way of making it easy to inspect the belt is to remove one of the "EARS" from the fan cover. I usually remove the one that is opposite the exhaust that way I don't have to go over the exhaust to inspect the belt. Use a knife or pair of wire cutters to clip the "EAR" off   just below the reinforcing.

With the ear removed and the engine TURNED OFF you can use
your - finger to reach in and check for fan belt tension and or inspect for damage or wear.

An improperly tensioned or worn fan belt can  result in a loss of horsepower and overheating. A belt that is too tight can result in incorrect ignition timing! Which could lead to engine failure. 

The Rotax maintenance schedule suggests the belt be checked every 25 hours of use.

To adjust the belt to the proper 1/4" deflection at 5 lbs pressure as per figure A use the Rotax fan wrench tool
 876 - 357 and the socket wrench supplied in your tool kit part # 876-210 to remove the nut, lockwasher, fan, and fan protector. 

To tighten the belt remove shims from between the two fan halves. On new engines these shims are placed behind the back fan pulley #8, on older model engines they can be placed under the lockwasher.
 

When reinstalling the fan and tightening the nut turn the fan over as you tighten down on the nut, or you will catch the belt, which could damage it. Once you have the nut snug use the fan wrench tool to lock the fan while you torque the nut to 40 ft. lbs.