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
How come nobody has MS Paint? ") One of the few useful programs
that come with Windows. How does one do screen captures without
MS Paint?
OK lets see if I got this right using Linux xpaint.
Looks like it will interfere John. Did I do it right?
--
Paul Lamar ...No rotor no motor.
Paul: You get a gold star next to your name for today! JP
Thanks JP. To recap the original problem was the belt
going to the side mounted alt. interfered with the mag. pickup.
First jpg. Aubrey scheme appears to work. Second jpg.
Paul Lamar ...No rotor no motor.
I agree the idler must be in between the crank and alternator pulleys
in order to clear the crank position sensor, as per Paul's second jpg
and my picture. So a self-tensioning idler would also have the
advantage of damping out unwanted oscillations compared to a fixed
idler pulley? The RX-8 does not have any springs in its two stock
belts -- just the adjustable idler you see in the pic, and a standard
adjustable alternator bracket.
Scott Gettings
Does the direction of rotation of an alternator matter? If not, you don't
need it hanging out the side of the engine. If you have the room between the
engine and firewall, you could mount it behind the engine.
Mark
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