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
I'm sorry Paul, I don't have MS Paint. If, in the image, you were to
rotate the green circle counter-clockwise so as to cover the heads of the
three bolts just right of the water pump, and up from the crank pulley, my
suggestion would be to locate the idler/tensioner in that location. The
drive belt would leave the crank pulley at about the 12 o'clock position,
make a wrap around the idler maybe about 270 degrees or so (the outside of
the belt would ride on the idler pulley) and meet the water pump pulley at
the 5 o'clock position. the water pump pulley may have 230?? degrees or
so of belt contact---. If the alternator were to mount as the image
shows, the belt should clear the crank position sensor. I assume the
sensor is between the pulley/belt and the cover. If not, I suppose the
sensor and the driving magnet could be moved to a more convenient
location. John Pletting
Paul: One other advantage for the idler/tensioner in that location is that
it is on the slack side of the crank pulley and can do the job of keeping
the belt at the tension it was set for without drive side oscillations that
Aubrey mentioned. I think that the water pump bearing load is a function of
how tight the belt is, and not the degree of belt wrap around the pulley. JP
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