You don't say what year or engine you have, but here are some guesses:
The starter motor has a pinion gear that moves out on the starter
shaft and engages the flywheel gear. The pinion gear moves out on
a thread on the shaft assembly. Inertia of the gear causes it to
move on the thread. When the truck starts and power is turned off
to the starter motor, the torque reverses and the flywheel spinning
the gear and a spring in the gear assembly causes it to screw itself
back away from the flywheel.
In other words, when the starter motor snaps on, it throws the pinion
out into the flywheel gear. The assembly that does this is called
the Bendix.
The noise you hear is from the pinion gear not completely engaging
the flywheel and grinding on it. The cause could be several things:
1. There is a weak battery.
2. There is a problem in the battery cables or terminals.
3. The starter motor switch (either a solenoid or a foot operated
switch depending on year and motor) is no longer making good contact.
4. There is a problem with the starter motor itself that doesn't
allow it to come up to speed fast enough.
5. The Bendix itself is covered with grease, thick oil, or dirt
and does not move freely.
6. The gear pattern on the starter pinion and flywheel do not match.
I don't know the details but understand this can be a problem if
a starter from a newer engine is used on a 216 AD motor.
7. The gear teeth on the starter pinion or the flywheel are very worn.
If all these are good, it pretty much has to work right.
Good luck.
Bruce Kettunen
57 3200
Mt. Iron, MN
At Monday, 9 July 2001, you wrote:
>From: W P. Fricke
>
>Every once in a while I jump in the truck and hit the starter button
and get
>this god-awful sound like someone just got "lectricuted". I will
depress the
>foot peddle a couple of times until I get the starter to actually
engage the
>flywheel. Then we're off. Yesterday it seemed intent on giving me
noise instead
>of action. Whats the problem? Open circuit? The gear is obviously
not engaging.
>I just don't know why. Bad starter? Short somewhere?
>
>The manual (for an earlier year) actual shows a starter with a solenoid
mounted
>on it with directions on how to adjust a gap in the starter gear.
My starter
>has
>no such solenoid mounted on the starter. Changes to later years
in the back do
>not comment on the starter. Suggestions?
>
>Patrick
>oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
>
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