When placing the alternator low on the cool side of a Renesis, an idler
pulley is necessary to avoid interference with the crank position
sensor. If a tensioning idler pulley is used, the alternator can be
fixed in place without an adjusting arm.

There is limited space to install a pulley, so a small unit is best. A
few units are small enough to possibly fit in the available space
(first 3 pics). Timing belt idlers are often smaller, lighter and
simpler (last pic).  Am I correct to assume that most timing belt
pulleys and their bearings are NOT designed to handle the loads of a
serpentine belt running the water pump and alternator?

Scott Gettings

Good work Scott. Thanks for all the idler pictures.

Yes.  Best use an idler designed for the job.

Paul Lamar ...No rotor no motor.

Paul & Scott,
 From this end of the engine, the rotation is CW.  The idler, as it was
depicted,  is on the driving side of the belt.  Using a spring loaded
idler pulley in this location could lead to some oscillatory behavior
unless it has a built in damper.  Also, re-locating the alternator  to
the side like this will increase the belt wrap angle on the water pump
and thereby increase the pump bearing load substantially.  So, it would
be important to set the belt tension at the lowest value that will
prevent slippage.  Toward that objective, you would want to maintain the
belt wrap angle on the driver pulley by moving the idler in the
direction I've sketched.   Finally, using the largest diameter idler
that will fit would minimize the rotation speed of the idler.

I've seen some fiber reinforced plastic idler pulleys recently that
weigh much less and are probably balanced better than the stamped steel
pulleys.

Aubrey Thompson

It looks like the original belt in the photo has very little wrap in the
stock configuration. The red line has more wrap which might be enough for
extra pumping load at the higher RPM.

John Gibbons

If the belt was slipping on my RX8 engine water pump I think
I would hear it squeal  at 9000 RPM. I could be wrong I guess.
The only way to check it is put an optical tach on it.

Paul Lamar

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