82 XJ alternator / tachometer issues

[tab1324]

I searched the threads for alternator troubleshooting and tested the voltage at the battery.. When bike is off, voltage was 12 V. I've been told that when the bike is running at above 2000 rpm or so, I should be getting about 13 V at the battery, indicating that it is charging. I did this test tonight and saw no voltage increase. Do I have a bad alternator??? Where can I get a new (or good used one)? Are there any other tests I should try before spending money on the alternator? The tach also doesn't work which I read is an indication of alternator failure. Also the warning light is on.

Please help. Now I've got it running sweet but have to work out the electrical stuff before it's road worthy.

thanks!

Tom B.

[Jerry]

The XJ uses a brush-style alternator, the XS models do not. Your problem may be as simple as worn brushes, which Yamaha recommends replacing every 10,000 miles. Brush part numbers are:

4G0-81611-10-00 Brush 1
4G0-81612-10-00 Brush 2

There are two tests for the alternator, one is voltage:

Volt meter at battery.
Rev engine to 2,000 RPM
Voltage should read 14.5 V (+ or - 0.3V)

Alternator winding tests:
Remove seat
Unplug alternator wiring harness.
Check field coil (green, black wires) by checking resistance, should be 4.0 ohms + - 10%
Check stator coil (white, white wires) with ohm meter, resistance should be 0.37 ohms + - 10%.
Resistance is given at 68 degrees F.

If you get no readings, or readings well in excess of these numbers, you may have to hunt up another alternator.

[tab1324]

measurements at coils

Thanks Jerry!

I measured the coils tonight and found the field coil to be slightly less than 3 ohms (about 2.8 I'd guess) which is out of spec. The stator coil measured right on. Temp was about 45-50 deg F. Any thoughts on my next step?

I assume the measurements are to be taken with the bike off??

Thanks!

Tom B.

[Jerry]

Yes, measurements are taken with the bike off.

Not sure which would be the best way for you to proceed. Alternators seldom go bad, and the few that I've heard about were due to the mounting screws working loose, leading to physical damage.

As far as I can tell the alternator is unique to the XJ, so you will have to look for one from a donner bike. If you look at an XS and XJ side by side you will notice the engine covers are different; the XJ left side (ignition pickup) is closer to the cylinders, or shorter, and the alternator side of the XJ is longer, or taller, than the XS due to the change in alternators.

Electronically the alternator has 3 internal 'legs', so it sounds from your measurements that one could be bad. The low voltage at the battery would tend to confirm this. Either a replacement alternator, or new brushes. I suspect if the brushes are bad the readings will be off, but the manual doesn't confirm this and I've never tested the theory. Neither option is cheap, though if you try the brushes first and it is not the answer you will have a new set to put in a used alternator.

[chevy45412001]

xj alts

do the xj's have external voltage regulators?and if so where can it be found? Sorry to cut in on your post Tom.

[Jerry]

The XJ, like the XS, uses an external voltage regulator. Although the XJ unit carries a different part number it looks like the 2 units are interchangeable. The XJ unit is rated at a higher current.

Location is near the fuse block. Regulator has 2 sets of pigtails. XJ part number is 10M-81960-A0-00.

[xj11DAN]

alternator problems

Hi, im new to the site but reading your alternator problems and i would suggest thr brushes. I have an 82 xj1100 that I love. I had the same problem last year and we could not find the problem, Yamaha shop was suggesting the stator amy be giong. We ordered a set of brushes from partsnmore.com and gave it a whirl. voltage came back up to 14.2 volts and i have had no problmes since.