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Re: [T3] New rebuilt Bosch generator

On 15 Dec 2003 at 12:19, Mike Wodkowski wrote:

> What my problem was in the end, was that the wire that connected the two
> fields in series was eaten through because it was pushed up against the
> ARMATURE windings, which ate through the insulation and then the wire.

Well, that's certainly not a good thing! Those parts will pretty much stay 
where you put them, but you have to put them in a good place to start with. Was 
this the generator I gave you with the engine? I recall that we took that 
generator apart and replaced the bearings, but I don't remember doing anything 
with that wire. I have to admit that I generally don't pay any attention to it, 
but there's no reason for it to move from the position its been in all along.

> Interesting note, I opened my original generator to run the Bentley tests on
> it, (and to see how they came apart) since Bentley mentioned that scorch
> marks across the armature could be caused by grounded armature.

Oh, I guess THIS was my old generator. WHEW...!   ;-)

> Funny, in the old gen, the wire connecting the 2 fields was completely bare.
> If this was pushed against the gen case, I'd imagine this would ground it to
> ill effect, no?

Correct, this would not be a good thing, but those wires are usually 
uninsulated and just carefully positioned so they don't touch anything.

>  Got no such reading. In fact, all the tests indicated that this generator
> was fine, outside of the fact that the commutator needed to be undercut. And
> the paper insulation around the field coils was ratty, but not eaten
> completely through.  Oddly, the scorch/scratch marks were where the
> undercutting was fine.

There's another test you can do if you have a pair of jumper cables.

Connect one end to the battery, black to -, red to +. Connect the other end of 
the black to the DF AND the housing (spread the jaws wide to do this.) Hold the 
housing in one hand while you touch the other end to the D+ terminal. You will 
get a hefty spark and the generator will turn.

The generator should turn smoothly. You'll feel the housing "lunge" as it 
starts up, but there should be no reaction torque after the start. If you feel 
the motor "cogging" or "lunging" any time after the startup then there is a 
problem with the armature which can probably only be fixed by replacing it. In 
general this means you should replace the whole generator with a rebuilt unit.

> I hate replacing parts without knowing which one was really the problem. 

I agree totally! I HATE not knowing why something failed, and I can't stand the 
concept of just throwing new parts at a problem until it goes away. 
Unfortunately, that seems to be the modern concept of troubleshooting.

I think I've just finished finding out what was wrong with my mother-in-laws TV 
set. It took me several hours and I had to buy the service lit on it for $10, 
but I just grabbed a couple of capacitors which I think will solve the problem.

Anyone "in their right mind" would have said, "It's 20 years old. Replace it."

I like our way better.   ;-)

Jim Adney
Madison, WI 53711-3054

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