New to XJ with Alternator problem

My first motorcycle was an 83 XJ750RK Seca. Four weeks later, I was hit from behind and the bike was totaled. So I found another 83 XJ750RK Seca, same color. This one has a problem in electrical system. I get two days commute before it dies on me (either at a light or while starting).

First mistake, I bought a new battery... done, right? Next, I pulled my Hayes manual and multimeter and checked voltage, resistance, and continuity (all terms I'm new to as a budding mechanic).

Meanwhile, I bought the salvage bike back for $225, so I have a complete bike for parts. I swapped the regulator to check that... no fix. So, I'm left to think it's the alternator.

This is where I am today. I plan to open the case and see the alternator for the first time.

I am asking for advice, tips, tricks, parts, guidance, and whatever else you'd give. What do I need to know?

 

First tip: before opening the alternator case start the bike, raise the seat and check the voltage with your multimeter at the battery terminals. You should get about 13.8 volts. Revving the engine a little higher should bring an increase in voltage. When you open the case there is a wire attached to the brushes which are mounted inside the cover you remove. Look closely at the alternator brushes for a score line across the width of the brushes. If you don't see it or if the end of the brush is very close to the score line then it is time to replace the brushes. Also check the large rotor which the brushes contact for any grease that may be causing a bad connection.

 

I've just been outside testing various things with my multimeter. First, I charged the battery then warmed the bike up to idle. Following this guide, I tested the battery at 2500 rpm (12.75 v), then tested it at 5000 rpm (12.75 v).

Some I've received advice from say continuity tests are pointless short of confirming there is at least one strand left in a wire.

I guess it's time to open it up.

 

The end-all and be-all of XJ electrical system troubleshooting, advice, and solutions can be found at:

http://www.geocities.com/MotorCity/Speedway/7795/

If I were you I would PRINT OUT a hard copy of the info as you never know when a page might disappear from the web.........

 

Tygor,
First thing I would do with your readings and symptoms is check your alternator brushes. If they are too short, you have an easy fix.
If they are fine and if you are reading 12.75 at idle and there is no change in voltage as you increase RPM, your regulator is shot (this voltage reading should be slightly less than the battery with the system turned off). If you had a dead alternator phase, you would see much less voltage as well since the system will load the battery down.
The Haynes will give you sufficient information and a troubleshooting matrix to follow. Use it well and let us know if you get hung up on anything.

 

I just got back from buying a new gasket (which is hard to find). And I've browsed a good portion of the guide recommended by Chacal. So now I am ready to break the seal and check things out.

Since I have a parts bike though, I have tried swapping out the regulator, and received the same results. If I remember correctly from previous meter tests, the rotor/stator tests (the three white wires and the brown & green), I get low readings for resistance.

So, once I open it up, I'll check for contact build-up and brush length. After that, I'll swap out the stator coil. I hope that does it, because I don't want to have to remove the rotor (since it requires special tools).

Thanks for all the advice guys. I'll continue posting in case another like me searches for a similar problem.

 

I may be done for the night. I took the alternator cover off, scrapped the gasket off, used steel wool to remove the dregs, and then used spray cleaner to get the gunk off. I read somewhere that if the bike goes down on it's left, oil can leak into the alternator fouling the brushes (as they absorb). The alternator looks pretty nasty inside, so this may have happened previous to my care.

The brushes look uneven, and I can see the scribe mark... at what point does the scribe mark tell you it's spent? When it is worn to the mark, or when the mark is visible beyond the plastic holder?

And finally, just for giggles, I ran a meter test on the stator... the were all below 2 (reading 1.2, 1.2, and 0.7). I had the ohms as low as the meter went. Again, from what I read, this is bad. But then I compared it to the parts bike (that I rode for 4 weeks without a dying battery, so I assumed the alternator worked). The parts bike read 1.2 on all three wires. Do I need to test the wires while the bike is idling?

 

The brush that rides along the "outer" surface of the rotor normally wears faster than the "inner" one, as the surface that the outer brush travels upon goes a greater distance than the inner surface. That is typical.

Once the scribe mark disappears on either brush, it's time for new brushes.....kinda like wear bars on tire treads.

The ROTOR resistance measurements (across the red and brown wires) should be 4.0 ohms +/- 10% (which equals 3.6 - 4.4) at 70-degrees F. Cooler temperatures reduce resistance measurements! So if it's 20-degrees outside you can't rely on those readings.

The STATOR (wire bundles) resistance measurements (across the three white wires, A-to-B, B-to-C, and A-to-C) should be 0.46 ohms +/- 10% (which equals 0.41 - 0.51) at 70-degrees F. All three "circuits" should have these readings. Cooler temperatures reduce resistance measurements! So if it's 20-degrees outside you can't rely on those readings. If the resistance readings across any three legs of the stator wires is zero, then you have a short somewhere, and for all practical purposes, the stator is toast. If you find infinite resistance, then you have an open circuit, which is sometimes caused by a loose terminal wire connection, etc.

If a stator has gotten a meaningful internal short, it usually overheats the insulation on the windings, which impart a "burned metal" smell to the stator, as well as having visibly burned areas of the epoxy wire insulation.

BTW, assuming things check out okay, it's a good idea to gently---VERY GENTLY----"clean" the copper surfaces on the rotor using some VERY FINE (like 800-1000 grit, wetted with WD40) polishing paper to get a nice bright contact surface for the brushes.

If you find that you need a new rotor and/or stator, I do have rebuilt ones available.

 

Oh, also, don't forget that most ANALOG (moving needle) ohm meters require that the ohm reading be "zeroed" before each and every use, and especially when you are changing the scale reading. Weak batteries in the meter will cause false readings.

Most digital ohmeters do not require zeroing, however, my experience with digital meters is that unless it is a pretty expensive digital meter, that the lower-cost "basic" meters aren't all that accurate.

In other words, for a given amount of money spent on an ohmeter, an analog meter normally outperforms a digital meter, until you get into the $100+ range........

Something to keep in mind!

 

You can also clean the commutator (what the brushes ride on) with a pencil eraser. Just wipe the eraser on your jeans to clean it after each wipe of the comm.

 

Well, it looks like it might get to 63 degrees today, so perhaps testing resistance won't be accurate until it warms up again, in the Spring. I'll play the guess-and-check game today, and hope I find a winning combination.

 

It doesn't change that much with normal variations from room temperature. It will be fine today. Make sure you have a base reading before measuring low ohm values.

Subtract the reading on the ohmeter before you measure the item.

 

Well, thanks to everyone here, I think I've fixed it!!! Double check me though (since the numbers weren't perfect).

Ok, first, I was a bit freaked out that I ruined the commutator with over scrubbing (even using the right grit and some electrical parts cleaner from the auto store). So I stuck to the pencil eraser and used the polishing paper for the build up (It was nasty, and covered with grime).

Victory two is that I was able to get it all back together and start the thing. Granted, the battery was a bit low at this point (12.3 before starting). It idled at 11.9 V, @2000rpm it was low 12 V, and @5000rpm, it was 13.6 V and climbing. Perhaps I should clean the commutator more. I failed to put the gasket on just in case it didn't work, so I have to go back in anyway.

Thanks for everyone's help guys. Now I don't have to salvage expensive parts from my other bike and still have a glimmer of hope that I can get 2 XJ750RK Secas up and running.

PS: I don't need both.

Oh, and Chacal, I was using a cheap-O meter, so I checked again today with a more expensive looking one I borrowed from a friend. The numbers we (almost) within range.

 

The voltage is still a bit low. I would ride the bike a bit and check again. You should hit 14 volts at some point below 4000rpm. With the alt gunked up it would be a good idea to check the connectors on the regulator/rectifier for corrosion. Low voltage will cause corrosion to form at the connectors.

 

Blue is correct.....still too low. You either have bad brushes or a bad battery or a bad regulator or bad connections or...........

This is why electrical problems are so frustrating to track down, there are so many possible sources. Follow the troubleshooting guides in the manuals and figure out what the real cause is and then replace. But congrats to you on making progress!

 

Well guys, it's over and the bike is back together. I tested the bad stator with the nicer meter and it read .4, .4, 1.2. I guess the 1.2 was causing my charge to be weak. So I put the good stator in the bike and it reaches 14 V at 2000 rpm. (From what I know of resistance, corrosion may be causing the extra bit. Is there anyway to fix the bad stator??)

My wife is glad that my jeans took a good amount of grime off of the bike, and she's even out there now polishing spots she would love to have re-chromed.

Thanks again for everyone's help. Problem solved. It was the stator.

 

You are on the path to fame and fortune!

Stators (as well as the rotor) can be rebuilt (rewound), price varies according to quality. If the stator plates are "splayed" or separated from each other or otherwise deformed, then there's no hope, and they just become very unique paperweights.

I sell rebuilt stators on a "core trade-in basis" if you're interested, they run about $135.00 plus $30.00 core charge if no good core is available to trade in.