Rotax 185 crankshaft

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    The initial production of the185 had a weak spot, The output shafts were snapping from the crank flange when imposed with moderate torque loads , this was not a problem when running the carbon bi props,due to there light weight, torsional vibration was minimal. But pilots being human and never satisfied in the their prusuit for better performance fitted better and consequently heavier props and soon found their new (investments) exiting stage forward, Coincidently the 185 in its industrial pump mode was also suffering the same fate,it seems that if there was a void in the water supply to the pump ,the engine would overspeed then as the water return hit the oversped turbine it would shock load it ,breaking the output shaft from the crank,(not good when ones fighting fire) this was probably more of a motivator for Rotax to fix the problem, then the problems the crazy people were having trying to get airborne.

   Below are some photos to help you instantly assess if your engine has the updated crank.

  This is the old syle crank ,note keyway on the output shaft ( left side), No keyway on new crank.
  If you have an opportunity to look at a older crank ,with the front bearing and spacer removed ,you willl spot the reason for these failures, the transition between shaft and flange
is extremely abrupt, leaving a very sharp corner where stresses can concentrate.

Results of the inevitable if you run these old cranks with heavy props

       To see if an engine has the upgraded crankshaft without removing anything ,look for a groove that is forged into the shaft just after it exits the case. Its hard to see in the photo,but you won't miss it,