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TR 3 polarity change

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bfitz

bfitz

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is it worth changing from positive to negative ground?
what changes need to be made to the gauges?
does the change affect starter performance?
relatedly, are there any conversion kits for the stock pulleys to use a modern belt? anybody ever try a Standard Ignition voltage regulator instead of the Lucas one?
Thanks,B
 
I have never changed the polarity and see no advantage unless you really want a particular negative ground sound system or you are looking to install an alternator.

If you do change it takes no time at all (the PO of my TR4 did it accidentally by installing the battery backwards). Car ran fine.

The only gauge affected is the ammeter which will indicate reversed. You can either switch the wires on the back or get used to reading it backwards.

You should also swap around the wires on the coil (rotating the coil 180 degrees makes this easier).

The motors (starter, wiper, fan) are unaffected by the change. The generator should be repolarized -- take about 10 seconds 'work'.

Not sure why you would want a 'modern belt'... the wide belt is readily available at any NAPA store and darn near indestructible. Some use the wide cogged variety -- might be quieter and easier to install.

Again, not sure why you would want to discard the Lucas voltage regulator. Most find them reliable and retain them unless they install an alternator.
 
I changed the polarity on my TR4 a couple of years ago. It takes about 5 minutes. Here's a link to the instructions I followed:

https://www.vtr.org/maintain/negative-ground.html

As Geo pointed out, unless you have a specific reason to change the polarity, there is really no advantage one way or another. In my case, I wanted to install a modern stereo, and I didn't want to hassle with trying to somehwo isolate it. Otherwise, I would have left the car as it was.

Oh... one more thing - I have an electric fan on my car, and I had to swap the wires around on it after the polarity change.
 
NAPA p/n 25-24379. Size is 3/4" x 38.5" or 19mm x 980mm.

This is a cogged belt.

I usually call first since they don't always have it on the shelf but can get it by the next morning.
 
I thought starter motors were series wound motors and consequently they would reverse direction if the polarity was reversed. (Same with wiper motors and heater blower motors.) Where did I go wrong?
 
Not sure what you're asking, Vettedog. I reversed polarity in my '57 TR3, and no change was required on the starter, fan or the wiper motor. (See Geo Hahn's earlier post in this thread.)

Mickey
 
[ QUOTE ]
I thought starter motors were series wound motors and consequently they would reverse direction if the polarity was reversed. (Same with wiper motors and heater blower motors.) Where did I go wrong?

[/ QUOTE ]
A series wound motor would reverse if either the armature OR the field were reversed. in this case, both windings are effectively reversed so the motor runs in the same direction. Some motors such as fan motors, have a permanent magnet instead of a field winding. Since you can't reverse the magnets the armature connections have to be reversed.
D
 
[ QUOTE ]
Not sure why you would want a 'modern belt'... the wide belt is readily available at any NAPA store and darn near indestructible. Some use the wide cogged variety -- might be quieter and easier to install.


[/ QUOTE ]
Hi Geo,
The wide belts tend to come off the pulleys at very high rpm. The narrower belts tend to stay on better. Also, the wide belt doesn't like to bend around small diameter alternator pulleys as well as the narrower. I'm with you, unless it is a race engine, the wide belt will likely be OK. I have a cogged wide belt driving an alternator & it works fine, but the engine doesn't turn over 5,500 rpm.
D
 
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