1981 CB750k not charging the battery

[cheesehead]

I traded my 1982 KZ550 LTD for this beast and it isn't charging the battery. I disconnected the stator from the R/R and my multimeter is reading 0.9 when i stick my leads in all combinations of the 3 yellow wires so I think that means the stator is good. I put a new battery on her and still o charge. I then took the stator cover off and put my multimeter leads on the copper rings of the rotor and it is reading 1.2 ohms on the rotor. From what I have read this should read 4-6 ohms, well above the reading I am getting. So I am pretty sure it is the rotor that is bad and I hope it didn't fry the new regulator that the old man I got her off of put on it already.

Now, my question is, I found a rotor on eBay off of a 1981 CB900 C and was wondering if this would fit my 1981 CB750 K. I asked the seller and he said it would fit perfect, but I am still a little sketchy about wasting $90+ if it doesn't work.

By the way my name is Brian, I am from Ohio and new to this site. Thanks in advance!

[cheesehead]

By the way, I am absolutely no mechanic by any means but I decided if I am going to own a bike, I am going to get a manual, tools, and and do things myself. While this might sound a bit odd, I am enjoying troubleshooting her, turning my wrench, and learning on the fly. I want to have this baby looking and running amazing by next summer. This charging issue is just the 1st of my things to do to her.  

[cheesehead]

I THINK I am doing this right, this is what I am doing/getting.

[cheesehead]

I need to know if this part will fit, basically.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=120746019969&ssPageName=STRK:MEWAX:IT#ht_500wt_956

[cheesehead]

Well, I looked up the rotor for both models using the parts source link listed in the main forum and both produced the same part #, so I ordered it and am just going to hope for the best.

[Lucky 1]

The Selenium rectifier on those bikes is usually painted orange or orange /red.
It is like a stack of flat plates.
If the paint gets cracked on the outside from twisting or over tightening it will not work anymore.


I was a dealer mechanic on those bikes .

You could just replace it with almost any modern regulator for Honda motorcycles about that size.
Check the stats.

[LukeM]

Donald, welcome to the forum. As a former mechanic for these bikes, your input on repairs and diagnoses is greatly appreciated.  Thanks for being here.

Luke M

[Cabreco]

donald branscom wrote

I was a dealer mechanic on those bikes .

You could just replace it with almost any modern regulator for Honda motorcycles about that size.
Check the stats.

Damn boys we got ourselves a TECH!

Welcome aboard Donald!
I recently joined myself, Great Forum with a  bunch of A1 guys!
You'll have a lot of fun here.

[cheesehead]

New rotor installed. I am now getting 13.5 volts at idle and 13.8 at about 4000 RPM. Yaaaaaaaa buddy!

[LukeM]

That sounds about right. It should be plenty to keep the battery in good shape. Go for a few rides and check the voltage periodically.

Good job!

Luke M

[Cabreco]

cheesehead wrote

New rotor installed. I am now getting 13.5 volts at idle and 13.8 at about 4000 RPM. Yaaaaaaaa buddy!

That's right on the money. If you can do a load test on the battery (Advance Auto can do it) just to make sure it's in good shape. The batttery that came in mine would work fine for a week then would give me weak start ups. (I hate that we have no kickstarts on these) So I had to spend $85 on a new one.
I also bought a 1amp trickle charger there for $23. It comes with the plug connector for the bike. Great thing since our seats don't tip up. Out battery access is a PITA.

You are on your way! BTW are you registering & insuring as an antique?

[sgtslag]

I had two of my bikes leave me stranded -- fortunately, both times were in town, not on the road, or on a tour.  As a result, I installed a Voltmeter on all three of my bikes.  The first two, I used a simple toggle switch as a bypass, to prevent them from draining the batteries over time, between rides, and over the Winter storage period -- not really necessary with smart chargers, but it seemed like a good idea at the time.

A Voltmeter will show you the health of the electrical system.  When the bike is off, before starting, the voltage should read over 12; when riding at 3k RPM+, the voltage should read 13V+, which indicates the charging system is working.  It may be old school, but it works.

Automotive Voltmeters (VM) will run anywhere from $10-$50.  They work, but their accuracy can be 1 volt off, so test them with a Digital Volt Meter, to know their margin of error.  My SunPro VM's are typically 1 volt low, so 12V on the gauge, is actually 13 -- a 12V reading, while running down the highway, would normally have me concerned!

On my Voyager touring bike, I spent the extra money, and I bought a Battery Monitor [http://www.amazon.com/Argus-BB-SBM12-PS-Battery-Monitor-Motorcycles/dp/B0029VY4G4/ref=wl_it_dp_o?ie=UTF8&coliid=I16GAB4M2A4J20&colid=23LKFMFR572JM].  It is supposed to test the battery at every start, showing a percentage of the life left in the battery...  That is the theory, anyway.  The lead-acid battery is around two years old, and it immediately read 48% life left in it, first time I hooked up the meter, and started the bike.  It alternates between displaying the percentage of life left, and the voltage on the battery.  The voltage reading seems to be accurate, against my Fluke 76 DVM.  It is also an LCD display, connected directly, without a bypass switch.  The LCD system drains much less amperage than an electro-mechanical needle gauge.

I am a firm believer in using a smart trickle charger on the bikes, at all times they are parked in the garage.  I use Battery Tender Jr.'s on both of my rides [http://www.amazon.com/Battery-Tender-021-0123-Junior-Charger/dp/B000CITK8S/ref=sr_1_1?s=automotive&ie=UTF8&qid=1310737638&sr=1-1].  They run around $28 + S/H (search the Internet for best price).  They are microprocessor controlled, 750 mA chargers, with three states:  full charge (at a low, steady rate), trickle charge (when the battery reaches 80%+ full charge), and monitor mode (senses the voltage, does nothing until it drops to a certain point, then it kicks into charge/trickle charge mode, auto-magically).

In the Fall, I prep my bikes for storage by adding SeaFoam to the gas, running them for a few minutes to get it into the carbs; then I top off the batteries' water (when these die, they will be replaced with AGM's -- no muss, no fuss, and 5+ years of life!), then connect the Tenders.  When I pull in, after a ride, I plug the bikes in:  the batteries' charges are topped off [fully charged], which prevents the lead plates from sulfating, which shorts out the plates, and kills the batteries.

The Kuryakyn LED VM [http://www.amazon.com/Kuryakyn-4219-Chrome-Battery-Gauge/dp/B000GU5WO8/ref=sr_1_1?s=automotive&ie=UTF8&qid=1310737072&sr=1-1] gets mixed reviews, but it is lower priced than the Argus.  It looks pretty nice, though.  Some folks claim it is inaccurate in its voltage readings (they're LED's, not a numerical readout, nor an analog needle on a scale, so they give an average reading of something that is less than stable when the bike is running -- they do a little fudging because of the Analog-to-Digital conversion used to determine which LED's to light up).  The other complaint I have heard is that they do not dim at night, as much as they should -- they're too bright, and distracting.  The Argus, on the other hand, has no lights, so you won't be able to read it without a flashlight, at night!  The SunPro automotive VM's [http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dautomotive&field-keywords=sunpro+volt+meter&x=0&y=0] have built-in lights, if you choose to use them.

A VM is relatively inexpensive.  It will let you diagnose the health of your electrical system in a very short time -- typically, a glance at the gauge, is all it takes.  When your battery is dying, it will forewarn you (the resting, pre-start voltage will be below 12V); when your alternator system is failing to charge your battery, it will warn you (the voltage will be less than 13V when driving down the road, at 3k+ RPM -- time to check the alternator, and the rectifier/regulator!).

For me, a VM is a standard upgrade from here on out; smart trickle chargers are standard operating procedure, while at home -- easy, quick, and they make starts much faster, and easier than they were without the bikes being topped off.  If the bike doesn't have a VM when I buy it, I will install one.  Once bitten, twice shy, Baby!  Cheers!

[cheesehead]

Thanks for all the info guys, I LOVE this site! I have a 1 amp trickle charger from AutoZone with the motorcycle leads that I bought the day I bought the bike because I knew of the issue. I will get a Battery tender Jr. at the end of the season, I didn't have the patience to wait on shipping. The battery in it is brand new, I bought it from AutoZone about a week or 2 ago. When I do most of my work over the winter I will add a better, more expensive battery to my "things to buy" list.

And Cab, I might register her as an antique. To be honest I still haven't got the title in my name fully yet because I've been working on it and couldn't really take it to get the VIN inspected (bought it out of state, I live on the OH/WV border) at the courthouse until I trusted it enough to ride it there. Next Friday I am going to take care of all my title/registration stuff. I'll let you know if I go the antique route or not. My back tire is dry rotted pretty good so I either have to order a new one payday or ride it to the local Honda shop.

[cheesehead]

And someone needs to help me name my 750!

[sgtslag]

Check the restrictions on licensing it as an antique.  In Minnesota, I could go that route with my '79, but I could only drive it on weekends, and to/from rallies/shows!  Some do it, and ignore the rules, but I would rather pay the nominal license fee, and not have to worry about getting a ticket (which would cost considerably more than the license fee...).

Rotted tires are a major safety hazard...  I would recommend replacing it before driving it.  I would also recommend the Pirelli MT66 Route tires, if they will fit your rims.  Do an Internet search for owner's comments.  Do a search here, for my comments.  They're the only thing I ride on, now -- too good not to ride on, IMO.  Cheers!

[Cabreco]

sgtslag wrote

Check the restrictions on licensing it as an antique.  In Minnesota, I could go that route with my '79, but I could only drive it on weekends, and to/from rallies/shows!  Some do it, and ignore the rules, but I would rather pay the nominal license fee, and not have to worry about getting a ticket (which would cost considerably more than the license fee...).

Agreed different states have different restrictions. In NJ my antique cars had little restrictions, here in Virginia I have a 250 mile from home restriction, not a big issue for the bike but I don't have to worry about inspection or annual registration fee.

sgtslag wrote

Rotted tires are a major safety hazard...  

Definitely fix this 1st or Cheesehead could be Cheese-spread in the blink of an eye!

[Cabreco]

cheesehead wrote

And someone needs to help me name my 750!

Well the only thing I immediately thought of for a guy with a blue bike, who's handle is Cheesehead...



<Notice the Silver & Blue>

[cheesehead]

omg that's great! lmao.

And trust me, I've just been putting it around town on the bad tires. I'll get new ones payday for sure.

[Cabreco]

Thought I'd drop this in Cheese's thread since it's related.
I picked up this inexpensive charging system tester at Y'allMart Online

Works great. Excellent way to test the battery & charging system on the fly for under $20

Equus Innova 3721 Battery and Charging System Monitor:

[sgtslag]

Nice thing about this unit, is that it can be moved from vehicle, to vehicle, as needed; it can also be removed during storage periods.  Only downside I can see is that it sticks out a bit, and may be prone to snagging.  Thanks for sharing, though.  Cheers!