Re: [XJ6 s3 4.2] Non-starter - Part 5

[Randy Wilson <randy@taylor.infi.net>]

>
>Measuring conditions: Don't have any aligator clips, so probes
>were jammed in place where possible. Also, car door was open.

Alligator clips make it a straight foreward one-man job. If you just
have the standard probes, you have to play the balancing act of jamming
them in place, or get some help, someone to turn the key.

>| Meter connected to battery. Less than 8 volts, bad/discharged battery. stop.
>| 10-12 go on.
>
>12.8 V

Battery is good. Good enough that the starter should do more than it is.


>
>| Meter connected negative to starter (mounting bolt is good), positive to the
>| lower big lug of the solenoid; actual power into the motor. 10-12 means
>| bad starter (stuck brush). Stop. bvelow 8, go on.
>
>0 V

No power getting to the motor part of the starter. Bad connection, where
is it?

>
>| Move positive to small screw wire (field wire). below 8 volts, bad relay,
>| neutral switch, ign switch. 10-12 go on.
>
>12.7 V

We are getting a signal to energize the starter....

>
>| Move positive to big top lug, battery in to solenoid. 10-12 v means bad 
>| solenoid. below 8 go on.
>
>12.8 V

And here's our power again. 


The solenoid preforms two functions. It is a fairly large electromagnetic
coil that move a big slug. The slug is connected to the starter drive
gear, such that when the slug moves it slides the drive gear in to mesh
with the flywheel. Also, when the slug gets to the end of it's travel, it 
closes the monster switch that engages the motor. The tests above show 
that the power needed to energize the solenoid is there, but the monster
switch is not closing. There are a couple of possible problems that could
cause this.

 Something is jamming the slug movement. This could be internal gumminess,
or the starter drive not meshing with the ring gear. 

 The internal windings of the solenoid are bad.

   These two I diagnose by the sound of the clunck when it attempts to 
engage. Bad windings, the solenoid will not clunk. With a bad ring gear,
you'll usually get a loud clang-with-ring as the teeth butt heads.


 Bad contacts for the switch internal.

 Bad contacts for the switch external.

You can make sure all the nuts on the two lugs are there and tight.
Everything is fairly clean. Internal problems will require a new
solenoid.


>| If the test proves it's either the solenoid or motor itself, try giving
>| it a good thump. Sometimes a brush will stick during shipping/storage.
>
>Gave it as much stick as I could in the severely limited
>space available.
>
>So, if this means I have a bad solenoid, what next? I managed
>to tap the solenoid a bit, but not much.


Tapping the solenoid is to cover the gummy part, and will also cover
bad switch contacts quite often. You need to hit it while the starter
is energized. I hit it by gently dropping a broken '70 Chrysler
front torsion bar on it from above (every tool box should include one
of these torsion bars; their powers of presuasion are legendary).

You can double check all of the connections, but, alas, it looks like
the starter is going to have to come back out. If/when it's out,
inspect the ring gear teeth. On a car this old, there will be wear
on the leading edge. You do not want to see missing, bent, or mushroomed
teeth.
 Next, bench test the starter. Come up with a suitable way to hold it still
within jumpercable reach of a good battery. I lay it on the ground and
use my knee. Connect the cables to the battery, the top solenoid post,
and the starter body (bolt ear is good). Jumper from the positive cable
to the solenoid field terminal (the screw terminal). The starter should
spin up. Note that this last connection will spark/arc a bit. Do not
use your favorite screwdriver. 
 If the starter does not spin up, disconnent everything from the starter.
Hook the positive to the lower solenoid lug, brace the starter, then 
quickly/firmly hook the negative to the body. This is a test of the
motor itself. It should spin without the drive engaging. Here, the last
connection is going to arc a lot during connection. This is why you want
to make it at the starter body, where precision is not critical. Do not
ever make the last connection at the battery. The sparks could cause 
the battery to explode.

>
>
>Nick


   Randy K. Wilson
     randy@taylor.infi.net

---

References:

• Re: [XJ6 s3 4.2] Non-starter - Part 5
• From: nick@sn.no (Nick Johannessen)

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