Testing for bad rotor - 3 ohm bad?

bkaushansky

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Read through Curly's post on charging system diagnostics. Can't run motor this late as kids in bed.

With motor off, 12.7V on battery, but ignition on and in run mode, 0.01 feeler gauge didn't' move, only one as small as 0.001 moved but weakly against the engine case. Brushes were ok, checked the rotor across the slip rings and got 3 ohms. Curlys says 5 - 5.5 ohm. Does this confirm a bad rotor?

BTW, '83 w/ TCI.

Thanks.
 
It sure does confirm a bad rotor. And unless your slip rings were squeaky-clean and you corrected your reading for resistance of the probes, actual resistance is probably less than 3 ohms.
 
Read through Curly's post on charging system diagnostics. Can't run motor this late as kids in bed.

With motor off, 12.7V on battery, but ignition on and in run mode, 0.01 feeler gauge didn't' move, only one as small as 0.001 moved but weakly against the engine case. Brushes were ok, checked the rotor across the slip rings and got 3 ohms. Curlys says 5 - 5.5 ohm. Does this confirm a bad rotor?

BTW, '83 w/ TCI.

Thanks.

Before you commit to an expensive replacement of the rotor, a couple of suggestions to verify your readings:

1. Remove the brushes when you measure across the slip rings. This will remove the regulator and associated wiring from causing a false reading.
2. Ohmmeters are not very accurate at reading low resistances, so i would go to Radio Shack and buy a couple of 10 Ohm resistors, twist them in parallel and measure their resistance (5 Ohms) as a check of your meter and measuring technique.

If you are still getting a low reading, then contact Gary at Custom Rewind in Birmingham, AL @ 800 798 7282 and order up a rewound rotor for $125 plus your core.

You will need a rotor puller tool which you can buy at www.mikesxs.com or ask Gary if his loaner is available.

You can do cheaper or more expensive that Custom Rewind, but you can't do better, and new is not necessarily better.
 
Pete,
Tested across slip rings w/ a Fluke 78. Checked multiple spots, same outcome 3.0 - 3.2 ohms. Thanks for Gary's contact info, but I believe this is a sign I need to go permanent. Have most of the parts already and was planning on the switch this winter.

I will be installing your ignition. What's the advantage of the higher output "Ultimate" black coil over the xsperformance green coil? Any disadvantages?
 
bk....,

1. The Black "Ultimate Coil" is more forgiving of running with one plug disconnected. If you catch it quickly, you will probably get away with it once or twice.

2. The "Green Monster" coil is absolutely unforgiving and will fry on the very first pulse with one plug wire disconnected.

3. The Ultimate coil is smaller and easier to install.

4. The Ultimate coil will continue to produce 82,000 at higher RPM's with the 60 degree dwell angle of the PAMCO. The green monster starts to fade at around 5,000 RPM, but we are talking fading from 75,000 Volts, so the output is still good up to red line. The Ultimate coil will still produce a usable output up to 10,000 or 12,000 RPM.
5. The green monster has a higher primary resistance, so it can also be used with points.

I have run both from time to time in my "81/H and my '78/E. I am currently running the Ultimate coil and I just like it better for the above reasons. I have also installed two of the Ultimate coils in my '74 CB750 to go along with my new CB750 ignition system and it really wakes up that engine. ( www.cb750ignition.com )

If you go ahead with the PM alternator, I would suggest that you initially connect the PAMCO and coil to an independent external battery when you first start it up because there have been a few cases where the PM alternator produced a very high (20 Volts +) output on initial startup and fried the PAMCO. After you have verified that the regulator on the PM is working properly with 14.5 volts, then go ahead and connect the PAMCO to the bikes electrical system. I also suggest that you wear safety goggles for the initial startup because the potential for a very high voltage can cause the battery to boil over violently and / or cause the capacitor to explode if you are going without a battery.
 
bk....,

1. The Black "Ultimate Coil" is more forgiving of running with one plug disconnected.

Is it possible to actually run with one plug disconnected? One side disconnected would mean the secondary isn't in a circuit.
 
Well I got a chance to run through the full "Curly" charging system post.

1. Battery charged to 12.7
2. 0.01" feeler gauge didn't move, only 0.001" moved and slowly - Fail
3. bypassed regulator via grounding the green wire. Throttled to 3K+, voltage at battery measured 14.5 -14.8 and kept increasing. Removed the bypass, voltage remained at 14.2 at 3K rpm and never really increased beyond 14.2V - Pass
4. Full battery voltage at brushes - Pass
5. slip rings measured at 3.0 ohm - Fail
6. 10.8volts on each white wire combination at stator - Pass
7. pass

Since the rotor measures out to 3.0 ohm and isn't completely shot, I'm guess that's the reason I still get a charging voltage of 14+volts at 3000 rpm. I hope this confirms a "damaged" rotor. Right?????

Thanks.
Boris
 
Is it possible to actually run with one plug disconnected? One side disconnected would mean the secondary isn't in a circuit.

The high voltage of the secondary will find a path to ground, over to the plug that is connected, across the gap of that plug and back to the secondary of the coil.

The internal path can be an arc across the secondary to the primary winding, which is a ground source either through the battery or the driving transistor. There is also considerable capacitance between the primary and secondary, so that capacitance can also be part of the completed circuit from the primary to the secondary and then to ground.

If the arc forms a carbon track from secondary to primary, then that is a short circuit and the coil is ruined.

In a lower voltage coil or one that is well constructed, the path is the capacitance between secondary and primary, so the one connected plug will get a spark without damaging the coil.
 
Well I got a chance to run through the full "Curly" charging system post.

1. Battery charged to 12.7
2. 0.01" feeler gauge didn't move, only 0.001" moved and slowly - Fail
3. bypassed regulator via grounding the green wire. Throttled to 3K+, voltage at battery measured 14.5 -14.8 and kept increasing. Removed the bypass, voltage remained at 14.2 at 3K rpm and never really increased beyond 14.2V - Pass
4. Full battery voltage at brushes - Pass
5. slip rings measured at 3.0 ohm - Fail
6. 10.8volts on each white wire combination at stator - Pass
7. pass

Since the rotor measures out to 3.0 ohm and isn't completely shot, I'm guess that's the reason I still get a charging voltage of 14+volts at 3000 rpm. I hope this confirms a "damaged" rotor. Right?????

Thanks.
Boris

Could be, but getting the full 14.5 volts with a partially shorted rotor may be difficult.

Did you verify your readings of the rotor slip rings with the brushes removed? Did you verify your meter accuracy with a resistor of 5 Ohms?
 
Verifyed the multimeter w/ 5 ohm resistor and validated w/ second multimeter. Measured yesterday at slip rings 3 ohms. Measured at brushes 3.1 ohms. Remeasured today at brushed 4.1 ohms on both meters. Weird.

What caused all this concern is what sounded like a missing ignition at idle and approaching a stop light w/ clutch in. Engine died as if someone shorted the plugs. Fired right up using electric start. Haven't been able to get plugs completely soot free. Today I measured the fuel level in the bowls and even though floats were set to 22mm (bS34), level is 3/16 below the gasket line suggesting a forced lean condition. I'm running XSJohn's needles w/ his 48.65 pilot, 2 1/4 turns out.

-b.
 
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