Is my rotor done?

[fullercameron]

I've got the bike pulled into the shop for some winter work. I started to have a charging problem about a week before I pulled it into the shop so I thought I would start going through things by checking the brush length. Brushes were both about 1/2" long. I thought that while I had the brushes out I should check the resistance on the rotor since I was already there. My rotor is measuring 15.8 ohms resistance ring to ring. This is obviously way above the normal resistance range I wanted to confirm that this is likely at least one of my problems. By the way, the rings were cleaned up with 500 grit paper and alcohol so they are both nice and shiny. The meter is a HF number but it appears to be accurate, if I touch the leads together they measure .5 ohms resistance, so I just subtracted that from the total # but this still looks toast to me.

The bike has all of the original charging system components. I have been thinking of adding a PMA system, but I am only really looking to change if it all seems cost effective and necessary.

Curious about your thoughts.
Thanks

 

[grepper]

Sounds toasted. There are some rotor rewind services out there, it's just shy of $100 to get it done. I had this guy do mine http://tpe-usa.com/ came back looking brand new.

 

[pamcopete]

fuller...,

Some meters are just not very good at measuring low resistance, like 5 Ohms. So before I would spend the money for a rebuilt rotor, I would go to Radio Shack and buy a couple of low resistance resistors, like 5 Ohm or 4.7 Ohms and use them to check the meter. You could also try a different meter for verification.

If it turns out that you do need a rotor, then I would suggest Custom Rewind in Georgia.

Custom Rewind
2014 Pratt Hwy.
Birmingham, AL
35214

800 798 7282

They also have a loaner rotor puller available.

Note: You should measure the resistance of the rotor with the brushes removed.

 

[gggGary]

I am going to agree; that is a suspect reading. Typical failure is LOWER resistance as the coating on the winding fails and it shorts internally. 2nd most common failure is open circuit (infinity) from a broken wire or connection. Like pete says meters are often inaccurate at low resistances. I have changed the resistance reading by 30% just by putting a new battery in the meter.

 

[fullercameron]

I'll grab a resistor and check the meter to see how close it is.

I am also just curious if the rotor is bad, given that I still have the stock rectifier and regulator, would the PMA actually provide a more reliable and easier to maintain alternative to the stock charging system?

It seems like there are a lot of people who are a fan of the older system, and I am curious if there are any distinct advantages to the stock style system.

I'll figure out the meter issue. Unfortunately I can't really check voltages on running components until I put the clutch back together.

Thanks again for the responses.

 

[angus67]

Here's a toast to Fullercameron's rotor!!
Even if the meter doesnt read accurately, That is so far off the scale, I'de say its toated.

 

[retiredgentleman]

I'll grab a resistor and check the meter to see how close it is.

I am also just curious if the rotor is bad, given that I still have the stock rectifier and regulator, would the PMA actually provide a more reliable and easier to maintain alternative to the stock charging system?

It seems like there are a lot of people who are a fan of the older system, and I am curious if there are any distinct advantages to the stock style system.

I'll figure out the meter issue. Unfortunately I can't really check voltages on running components until I put the clutch back together.

Thanks again for the responses.

I've been using the stock alternator for the last 6 years, and it works just fine. I installed a new rectifier (2 bridge rectifiers), and a NOS, solid state, automotive regulator. The only maintenance, is once a year I polish up the slip rings and measure the brush length. It also helps to reduce the alternators load....................change out the stock tail light and use an LED tail/brake light.

The original rectifier and regulator on your bike have done their service and its time to retire them. That old rectifier is robbing you of voltage, and the mechanical, relay type,
regulator has springs and contacts, which go out of adjustment. Yes, they work, but they are not the best.

If you find you have to start buying parts, such as a rotor and/or stator, then you could compare the cost of switching over to a PMA. New parts such as a PMA, will of course be more reliable than 30+ year old stock alternator parts.

Many lads on the site seem to have a fear of brushes and stock alternators, however, I find mine to be very reliable.

 

[XSLeo]

From all I can tell by reading as much as I can, the PMA's only advanatage is that you can run without a battery.
Leo

 

[xsfanman]

Not really, I just installed Hugh's PMA and it charges great at idle. only 1000 RPM's. I was able to change my headlight to a 55 watt and with my electric heated vest It kept the battery perfectly charged and I perfectly warm.
This spring I will put it to the real test

 

[pamcopete]

Advantages to a PMA:

1. No brushes to wear out and be replaced.
2. No slip rings to keep clean in order to fully benefit from the available Amps from the alternator.
3. Generally a higher Amp output at low RPM's
4. Installing a PMA kit means all new charging components.
5. If desired, no battery needed with a kick only capacitor setup.
6. Stress on the PMA does not increase with an increase in load.

But, I have managed to keep my stock alternator system working on four of my five bikes without any particular effort. The other bike has a factory PMA from Honda. The stock alternator does not produce wasted power and heat. The PMA produces it's maximum power at all times.

 

[grepper]

BTW: The rotor I had done was for a Honda CB. Currently I have two xs650s that I ride and both using the stock origonal rotor just fine.