[AT] Farmall starter switch

[Dean Vinson]

Nuts.   Got to thinking, "That might just be a bit too easy," so I went back
out, reconnected the starter cable to the battery, and touched the other end
of the cable to the bare post on top of the starter motor.   Big sparks but
no response from the starter motor--so my theory that the switch simply
wasn't making contact appears to be incorrect.  Time to take the starter
motor off, but that's a task for another evening.

Before doing anything tonight I'd once again tried to start the tractor
normally, and watched the ammeter while doing so.   Nothing.   Ammeter
deflected just fine when I turned the lights on, so I'd assumed the lack of
any noticeable deflection when I pulled the starter switch meant there was
no current flowing and the problem was in the switch itself.   But bypassing
the switch sure didn't get that starter motor moving.   Did make a new
little arc divot in the top of the post on the starter, though.

Dean Vinson
Saint Paris, Ohio


-----Original Message-----
From: Dean Vinson [mailto:dean at vinsonfarm.net] 
Sent: Wednesday, July 23, 2014 9:22 PM
To: 'Antique tractor email discussion group'
Subject: Farmall starter switch

The Super M wouldn’t start the other day, wouldn’t even show any sign of
trying to turn over, despite plenty of battery power.   Tonight I had time
to take the starter switch off the starter motor (this is a late Super M,
with the switch mounted right on top of the starter motor, rather than
behind the fuel tank support like on an M or early SM).   The spring-loaded
copper contact plate inside the switch and the copper post on top of the
starter motor are both all chewed up where they come into contact when the
switch is pressed.   I assume an electric arc occurs when I make or break
that connection, probably boosted quite a bit by the tractor’s 12-volt
conversion, and over time those arcs have removed enough material that the
contact plate simply doesn’t reach the copper post any more so the starter
motor never receives the “go” signal.    Anybody ever run into something
like that?  

http://www.vinsonfarm.net/photos/SM_starter_switch_post.jpg
http://www.vinsonfarm.net/photos/SM_starter_switch_housing.jpg

Coincidentally enough, some years ago the starter switch on the 1950 M I had
at the time quit working--but it was the opposite problem, too much
electrical contact rather than not enough.  I fixed that one by replacing
the worn-out cardstock insulation with some polystyrene modeling sheet, to
keep the moveable switch plate from directly shorting out to the switch
housing:

http://www.vinsonfarm.net/photos/M_starter_switch_1.jpg
http://www.vinsonfarm.net/photos/M_starter_switch_2.jpg

This time I think I’ll look for a replacement switch and hope the post on
the starter motor is okay for a while longer... seems like that’d be the
easiest fix.

Dean Vinson
Saint Paris, Ohio