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

Hi Gentlemen---I've been following the discussion  of many topics for the
last six or seven months and thought I might throw out a suggestion for the
idler/tensioner issue here---What would happen if the tensioner were mounted
on a plate just to the right of the water pump in the image, and driven off
the other side of the crank pulley, then to the water pump and alternator?
With that arrangement, the alternator could mount a lot lower if there is
room in that position.  Many automotive applications use one tensioner for
one belt that drives everything hanging on the engine, and are quite
reliable--- Just a thought---John Pletting

I can't quite follow you here John. Can you make a sketch in
MS Paint? Is the water pump going to rotate in the right direction?

Paul Lamar ...No rotor no motor.

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