Mike,
I will measure my e-shaft pulley when I get home tonight, but I'm sure it
is larger than 4.5".  I wouldn't be too concerned with a 10,800 rpm's max
for the alternators, but with a 5.5" (17.28" circumference) e-shaft pulley
and a 2.5" (7.85" circumference) alternator pulley, the ratio is
2.2:1.  So, the alternators would be turing 15,840 rpm at 7200 engine
rpm.  That is 58% over the 10,000 rpm figure.  That what makes me nervous.

Since multi-V belts have become so commonplace, I feel certain that I can
find something around 4.5" that I can adapt.  Guess I'll have to make a
trip to Pic-A-Part and see what I can find.

Mark

At 02:03 PM 5/5/2004 -0700, you wrote:
>The alternator speed isn't a problem, it doesn't care how fast you spin it
>(unless you have an alternator that is way out of balance).  On my RV-4
>with Lycoming engine the alternator is over-driven about 4:1, I have the
>2-1/2 inch stock alternator pulley, the crank/ring gear pulley is about
>10" diameter so the alternator will see 10,000 at cruise.  This is typical
>of most Lycoming installations on experimentals and is not a problem on
>thousands of planes.
>
>My e-shaft pulley is 4-1/2 inches dia.  I think it is a stock pulley as
>the timing pointer is at the edge of the pulley.  That makes the
>alternator over-driven at 1.8:1.  Using a 6000 rpm cruise with my RD-1C
>that makes the alternator spin at 10,800.  Close enough.
>
>There are enough Lyc drivers that were uncomfortable with this that
>someone makes a 4" pulley for the alternator.  Aircraft Spruce 02-03
>catalog page 245, p/n 07-06828 $48.95.  (A waste o' money except for the
>feel good factor.  If you'll accept MY explanation I'll accept your 48.95
>and SAVE YOU shipping costs!
>P-)
>
>Regarding water pump speed, I've been working on this for a few weeks with
>my 13B dynafocal adaptor.  I've mostly come to the conclusion (yet open to
>more data or ideas) that the factory pump and pulley are sized to provide
>the needed flow capacity at any given engine speed at the horsepower
>levels we are running at.  So, to make it easy I'm sticking with the stock
>pump at the stock pulley ratio.
>
>Mike
>Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR
>13B in gestation mode, RD-1C, EC-2
>
>At 12:06 2004-05-05, you wrote:
>>Well, that's interesting.  This reminds me of a nagging question I have
>>had, but haven't asked.
>>
>>I was curious about the need to go to a smaller crank pulley to slow down
>>the water pump and alternators.
>> From memory, the crank pulley is about 5-1/2", the alternator pulleys
>> are about 2-1/2", and the water pump
>>pulley is about 4" diameter.
>>
>>So, running an RD-2C (2.85 ratio), the alternators will be turning about
>>20k during climb-out and the wp will be turning
>>about 10K rpm.  That seems too fast to me.  I could probably find larger
>>pulleys for the alternators, but
>>then there's the water pump pulley.  Your unplanned experiment would
>>suggest that we can run the wp slower
>>and still cool adequately.
>>
>>This brings me to a second option.  I think a simpler approach would be
>>to reduce the size of the crank pulley.
>>The problem is that I haven't found a multi-V reducing pulley at any of
>>the after-market suppliers.  I really don't
>>want to change over all the multi-V pulleys to single V pulleys, but that
>>is one option.
>>
>>Another solution might be to find a smaller pulley from another vehicle
>>and adapt it to fit the rotary.  If that doesn't
>>work, I could have one made.
>>
>>So, am I worrying about nothing, or is this a real problem?
>>
>>Mark
>
>
>
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