Message-Id: <5.1.1.5.2.20040524104615.02c06008@localhost>
Date: Mon, 24 May 2004 11:09:31 -0500
To: Fly Rotary <flyrotary@lancaironline.net>
From: Mark Steitle <msteitle@mail.utexas.edu>
Subject: Slowing Down the Alternator
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This is a follow-up to an earlier thread about alternator rpm's.  For the 
record, my engine is a J-spec 20B.  The crank pulley is 5.5" dia., 
multi-rib design.  I'm running two 55 amp Geo ND altrnators.  These 
alternators have a shaft size of .594" and came with 2" pulleys.  I had 
calculated that they would be turning approx. 21k rpms on takeoff and 
climb, if they lasted that long.  So, I set out to find larger 
ones.  Bulent suggested the Honda Prelude alternator pulley as a suitable 
replacement.  It has a diameter of about 2-3/4".  I found one on ebay, bid 
and got it.  It came with two stock belts and a stock power steering 
pulley... all for $5.50.  Not bad, if I could use it.

When the items arrived, I discovered that the Prelude alternator pulley had 
a larger hole size and wouldn't work without a bushing.  However, the power 
steering pulley had the right size hole, and was about 3-7/8" 
diameter.  This would result in about 10K alternator rpm on takeoff.  Only 
one little problem, it had splines about half way down the hole to match 
those on the power steering pump.  The rest of the hole was smooth and the 
right size. So, 15 minutes of lathe work (thanks Bob) and the bores mated 
perfectly.  Problem solved.  Install a longer belt and its done.  Now to 
repeat the process for the other alternator.

A side note... the Prelude alternator pulley is the correct size for the 
Mazda alternator.  So, I gave it to Bob.

Mark S.