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Old 04-14-2008, 05:19 PM   #1
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'72 CB450 Charging System Troubles

Hey guys,
Got a '72 CB450 that isn't charging the battery and I'm trying to track down the cause. Unfortunately the cb450dohc.com site shut down for some reason and the remaining MSN site is kinda iffy.

The symptoms are that when the headlight is off, at idle the voltmeter will pretty much break even on about 12.9-13.0 volts at the battery. When you rev it goes up a little but it's not where it should be (13.8 volts at least). Charging current at idle is about 0.9 amps. When you rev between idle and 2000 rpm or so charging current goes up to about 1.2-1.5 amps. Where it gets interesting is that at about 3000 rpm charging current nosedives to 0.5 amps and never goes above that again. Charging current spec with the headlight off is 3-4 amps at 3000 rpm and 4-5 amps at 5000 rpm.

Now, with the headlight on, you can forget about it. If you have a voltmeter hooked up to the battery with the engine idling and you turn the headlight on, the voltmeter starts counting backwards -- clearly the battery is discharging. Same thing with charging current, turning the headlight on will put it to about -2.5-3 amps and it never goes positive regardless of rpm.

Here's what I've got so far:

New Yuasa battery, fully charged.

Bike starts and runs great (on the kicker, the electric starter clutch is busted - that's another future fix). That is until the battery gets discharged enough so that the coils don't work anymore.

I electrically tested the rectifier as instructed in the Clymer manual. This was my first suspect as I hear the rectifiers were a weak spot on these bikes. Rectifier tested good as per the specs in the manual.

Next thought was maybe the headlight switch. Here's why: these bikes have a split charging system. In stock configuration, with the headlight off, you get half of the charging system's output. With headlight turned on you get full charging output. I decided to wire the 36-year-old headlight switch out of the equation and connected the 2 wires in the headlight bucket that the headlight switch bridges when you turn the light on. This should provide full charge all the time. It made no difference to my readings with the meter.

Next, tested the stator for shorts and opens, again as per the Clymer manual. Step 1 is to read resistance between the yellow and pink wires. Spec is 1.1 ohms, and mine was right on that. Then you measure between the white and pink leads and spec is 0.55 ohms. Mine read 0.4 ohms. I don't know if that's a significant enough difference to be a problem. Any thoughts? I have a spare stator here that reads 1.1 ohms and 0.6 ohms (my meter doesn't read 2 decimal places at that scale). I am thinking of replacing it and fixing the starter clutch while I'm in there.

So really the only items left are the voltage regulator and the stator/rotor combo. I have a spare stator and rotor and I may swap that in for shits and giggles but I'm not real optimistic becuase the electrical testing seems to indicate that it's OK. The other possibility is the voltage regulator. Clymer doesn't give any sort of test procedure for it. They just suggest that usually voltage regulators fail so that the charging current is too high rather than too low. But that seems to imply that it's possible it could fail the other way. Unfortunately they don't mention a way to test it. Any ideas?

Does anyone know if these bikes used an old-skool points-type regulator or a solid-state type? I would guess points-type.

Oh also I tested the output of the alternator directly at the plug where it ties into the bike's harness to eliminate all the other questions from consideration. At idle, on the pink to yellow voltage test I got 20 volts AC and on the pink to white test I got 18 volts AC. However without a spec these numbers don't really mean anything to me. Are they normal? Low? Not enough information? I just don't know.

Any expert advice from you old Honda gurus would be much appreciated.
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Old 04-14-2008, 10:22 PM   #2
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Write to Tony over at Oregon Motorcycle Parts. He makes modern regulators and rectifyers for vintage bikes. The honda twins are known for having a lame charging system, never meant to run with the lights on at all times either. I switched to a modern rectifyer with some decent result but still like to trickle charge once a week or so. Tony had mentioned that the output of the system is so low that you could probably remove the regulator with no ill effect. Another thing to check is that all connections are clean, every little bit matters with these. Check out his site here: http://www.oregonmotorcycleparts.com/

Just saw that you are in Brooklyn, check out: www.NYCvinMoto.com it's a mailing list for the NYC area vintage riders. We all ride, race, restore and wrench on these old beasts. Also meet up at Bar Matchless in Greenpoint on mondays to watch the Moto GP. Swing by sometime. If you ever need any cb450 parts let me know, I have plenty.
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Old 04-15-2008, 04:01 AM   #3
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Hey ROSKO,
Thanks for the info about Oregon Motorcycle Parts. I was not aware of that site before. I may buy a rectifier and regulator from him and replace them just on principle.
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Old 04-15-2008, 03:44 PM   #4
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So I ordered a rectifier from the Oregon Motorcycle Parts guy. I figured $22 for a plug & play solution was worth it just for my peace of mind. Plus it's easy enough to replace. I'll try that before I delve into the stator. I don't really expect the recitifer will fix the problem but man it would be nice if it did.

He doesn't make a regulator for the CB450. I wrote him an e-mail and he said he doesn't make one because the charging system is so weak you can run the bike without one. I find this to be a highly dubious statement and I'm quite sure Honda wouldn't have put one on if it didn't need to be there -- they were building these things to a price back then. Not worth blowing all my light bulbs out to prove the guy wrong.

So I guess if the rectifier and the stator don't fix it I'll be attempting to source a voltage regulator just to rule that out at the very least.
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Old 04-16-2008, 09:39 AM   #5
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My guess is voltage regulator. They are solid state, and you could certinaly bypass it and see what happens. Even in full tilt the charging system might put out 5 or so amps, so you shouldn't hurt anything.
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Old 04-16-2008, 09:45 AM   #6
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From the ancient depth of my honda riding memories from my 20's

I had a similar failure on my cafe'd CL77 that turned out to be a bad ground wire......

And in a similar but also perhaps not related way, I had a good friend with a pretty clapped out CB450.... when he went to remove the tach cable after it quit working he couldn't get the bike to run and had zero power unless you shook the bike...

Turned out that his steering head bearing were totally shot, and when the tach cable was removed the bike was attempting to ground all of the instruments through the steering head bearings and failing! There seemed to be no additional grounding through the wiring harness. We ran a ground to the frame from the cluster and he rode away.

He still has the bike, and still hasn't replaced the bearings!
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Old 04-16-2008, 03:58 PM   #7
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Have you even checked the stator yet?
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Old 04-16-2008, 04:32 PM   #8
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Quote:
Originally Posted by Inane Cathode
Have you even checked the stator yet?
Yes. See original post.
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Old 04-16-2008, 04:35 PM   #9
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Quote:
Originally Posted by Jeff51
My guess is voltage regulator. They are solid state, and you could certinaly bypass it and see what happens. Even in full tilt the charging system might put out 5 or so amps, so you shouldn't hurt anything.
So how would I go about bypassing it?

According to my wiring diagram I've got 3 wires going to voltage regulator. Yellow wire direct from alternator, Red wire from battery, and black wire that ties into a bunch of shit, looks like that is also 12v but from the ignition switch.
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Old 04-16-2008, 08:18 PM   #10
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Hey guys,
I could use some help interpreting this wiring diagram with regard to the charging system. I'm pretty good with mechanical stuff and electrical stuff but voltage regulators have always been sort of mystery boxes for me. Based on the diagram below (click for larger version) can anyone tell me how this thing works and how I might go about bypassing it to see if it's faulty?

It's been so long since I worked on old Volkswagens that it seems I've forgotten a lot of what I learned back then. I also got used to newer current track wiring diagrams instead of this type.

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Old 04-17-2008, 06:53 AM   #11
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here, color makes this one a bit easier:
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Old 04-17-2008, 08:14 AM   #12
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Quote:
Originally Posted by The Jerk
So how would I go about bypassing it?
I'd just unplug the whole thing. I'm not sure exactly how the regulator regulates, but without it you still have a complete charging system. Not that I have tried this mind you... If anything I suspect the original rectifier to be the weak link on the system, but the new one you mentioned shouldn't have a problem handling the full output.

If you convince yourself the regulator is the problem, you might try playing with the adjustment screw on it. If I recall it has a big glob of goo over it to keep you from messing with it...
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Old 04-17-2008, 02:47 PM   #13
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ROSKO, nice wiring diagram! My Clymer has a color diagram in the back but it sucks; it has no terminal numbering or anything. Where'd that one come from?

Last night I did some more online research and what I found seems to indicate that the selenium rectifier can cause weak charging symptoms even if the diodes inside are only flowing current in one direction. I am more and more thinking that a new rectifier may very well fix the problem. I am going to hold off on installing the spare stator until I get the new rectifier in.
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Old 04-18-2008, 12:13 PM   #14
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Kind of an unrelated question, but all the above wiring diagrams show the headlight switch as having 4 positions: Off, Low, Neutral, and High.

WTF is Neutral? My headlight switch has 3 positions, Off, Low and High. Anybody know what N is supposed to be?
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Old 04-18-2008, 01:43 PM   #15
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Quote:
Originally Posted by Jeff51
I'd just unplug the whole thing. I'm not sure exactly how the regulator regulates, but without it you still have a complete charging system. Not that I have tried this mind you... If anything I suspect the original rectifier to be the weak link on the system, but the new one you mentioned shouldn't have a problem handling the full output.

If you convince yourself the regulator is the problem, you might try playing with the adjustment screw on it. If I recall it has a big glob of goo over it to keep you from messing with it...

The regulator regulates by taking the relatively high voltage output of the alternator and regulating it to something nominal, like 14v.. that wont fry the battery or the bikes electrical system. It acts sort of analogously to a gas flow regulator. So I would qualify your statement that you "still have a functional charging system without one" by saying you have a "temporarily functional one, till the battery gets over-volted and dies."

In any event, you should be able to test if the regulator is working by bypassing it and seeing if your voltage at the battery is >15v at revs. Then check it while back inline, and it should read 13 or 14v at the battery anywhere above a minimum rev.


I'm thinking you would bypass the regulator by making a small jumper wire to go between the red and yellow wire terminals in the connector, because I think the black is just a ground. But I would look back in my old BMW charging system files to know which wires to jump... I would have to remember the principal to tell which wire came from where, etc...Its the same test for a BMW regulator, they're not different in principal, only details. No doubt its googleable.
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