From: "Neil Unger" <flyrotary@lancaironline.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: belt slippage
Message-ID: <d36e9042-3a88-337c-326f-26da233ec052@gmail.com>
Date: Sat, 19 Aug 2017 15:50:56 +1000
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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.