Mailing List flyrotary@lancaironline.net Message #63638
From: Neil Unger <flyrotary@lancaironline.net>
Subject: belt slippage
Date: Sat, 19 Aug 2017 15:50:56 +1000
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Mat,  funny the things you find when you actually look!  Found 2 causes for my fan belt slipping and not driving.  First are the pulley sizes.  Main drove pulley on E shaft is 100mm.  Then my so called reduction pulley on the water pump is also 100mm,  should be 115mm to get the magical 15% reduction.  Having said that the original steel pulley is around 90 mm for the water pump.  Then the pulley on the alternator is a solid little 55 mm dia, whereas it is supposed to be 80mm.  Price in OZ for the two reduction pulleys (Water and alt) is $110 AUD .  Then the second revelation is that even with the belt at normal tension I can turn it quite easily, due to the fact it is a 5 rib multi rib belt.  Problem is the lovely machining on the pulleys, that have not had the apex of the grooves machined off ( they remain very pointed) to allow the belt to settle down into the grooves and drive on the "V " sections in the belt.  It is attempting to drive on the apex of the grooves only.    I should be shot for not seeing that.  Neil.

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