Date: Tue, 23 Dec 2014 00:45:47 -0500
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Trying to understand starter stuff
In-Reply-To: <CAEwp_cQB86erjTxJd52jd0v2TOdW6wLr39Gyj9HYT1+wVp0dvQ@mail.g
mail.com>
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At 11:03 PM 12/22/2014, Marc Perdue wrote:
>Hi all,
Excellent! I now have three verified cases of a starter control lead
coming off without causing a hard start failure: your Van, my '89
2.1l, and my '71 Fiat 128. I solved that one after running out of
gas in an uphill line to buy gas somwehere in upstate New York, when
it became clear that the motor would crank if it were torqued
slightly sideways.
Starters have some challenging necessities. They have to have big
cables direct to the battery; a heavy switch that can switch them on
and off under load without burning up quickly; a means of engaging
the pinion into the flywheel ring gear; and a positive means of
disengaging it when the motor starts, so the starter doesn't burst
from overspeed.
Back when the world was new the electrical switching was done by a
heavy-duty relay that would today be called a contactor but was
commonly known as a solenoid. It was mounted somewhere between
battery and starter, and a light wire from the starter button or key
switch used to activate it. For testing you could use a screwdriver
to jumper between the big battery cable connection and the control
terminal. Starter "solenoids" were a commonly available FLAPS part
and no doubt still are; as they regularly failed in use. Last one I
bought cost three or four dollars. Excellent for switching a couple
hundred amps DC but not rated for continuous duty. They're meant for
starting cars, once per trip segment, plenty of time to cool in between.
Engaging and disengaging the pinion was accomplished by a clever
invention called a Bendix drive. The pinion was mounted on the
starter shaft and engaged a pair of helical slots in the shaft. It
was kept wound down to the bottoms of the slots by a light spring
that pressed it away from the end of the shaft. When you hit the
button, the shaft would spin violently and hurl the pinion into
engagement during the first few revolutions. And when the motor
started, the ring gear would spin the pinion back down the track out
of engagement. It worked a treat, so long as you kept it clean and
not gucked up with oik or grease. The Bendix Corporation waxed fat and happy.
Came the day that someone thought it would be better to combine
actions. If the contactor were mounted on the starter it would
simplify wiring, and it could be used as a real solenoid, to
physically throw the pinion into engagement as well. Or rather a
solenoid could be thus used, and with some contacts added could
perform the contactor function as well. An overrunning clutch would
handle decoupling the starter from the engine, leaving the pinion in
engagement but not forcing the starter to keep up with it. Full
disengagement would happen when the key was released. Over a decade
or two this method largely took over for starting cars, and that's
how Bosch did it on our starters.
The big cable goes direct from battery to starter, where it meets the
thinner wire from the alternator that supplies charge. That
connection is subject to corrosion. The ground connection through
the starter, bell housing, transmission ground strap may be
defective. The solenoid itself wears and gets crudded up; you have
to take the starter apart to clean it up. Non-A/T versions of this
starter have no bearing at the pinion end; the shaft inserts into a
sleeve bearing that's in turn inserted into the bell housing of the
engine. That wears and needs renewal. And the solenoid gets its
operating power not from that fat cable but from battery to panel to
ignition switch and back to the starter. It only needs two or three
amps, but it's a long trip. It's easy to see if a relay could help
it -- just jumper the alternator B+ post to the starter control
terminal. You can reach it by reaching your hand over the top of the
bell housing, quite a way forward and then to the right. There's
probably a spare terminal to latch on to. If it cranks snappily that
way and listlessly by the key, add a relay. If it makes no
difference, neither will the relay.
Yours,
David
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