Motorcycle Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
29 Posts
Discussion Starter #1
I've been having issues with the electrical on my 1978 Honda CB400.

The problem seems to be related to the charging system. After riding for awhile the battery is dead and it's a new battery.

I tested the charging system per the manual with the bike running and the readings were all out of whack. The bike is supposed to be putting out like 5 amps at 5,000 rpm, my ammeter registered -1.37. That didn't seem right, so I tested the stator and it failed too.

The resistance on all of the connections tested within range, except the Green-Blue. It isn't supposed to be greater than 130, but registered at 540 ohms.

I haven't testing the regulator/rectifier yet, that's for tomorrow night.

What I'm wondering is, do I need to replace the stator or can it be fixed? I don't know much about electrical stuff, so I'm not sure what would cause the resistance to get out of spec. Do stators just get old and fail?

Any advice would be great. It doesn't seem like too hard of a part to find, but not super easy either.

Thanks.
 

·
Save them all!
Joined
·
4,278 Posts
Quick and dirty test of the actual stator output, unplug the main connector there and test the AC voltage with the engine running between the three pairs of yellow wires. You should get something fairly high.

You should have good continuity between the three pairs also, but none to ground.

Stators can go bad after a while - the insulation between the wires breaks down and the windings short against themselves and the engine case. It does happen.

Do you know if you have a permanent magnet rotor? Or a field coil?
 

·
Registered
Joined
·
29 Posts
Discussion Starter #4
Call a pro

I think I'm over my head with this issue. I'm going to bring it in to the shop and let a pro figure it out. I'm afraid I'll end up doing more damage than good.

I'll post what the culprit turned out to be in case anyone else runs across a similar issue.

Thanks,
Keith
 

·
Premium Member
Joined
·
5,274 Posts
Probably a good idea, if you can find one that knows about your old bike.

FWIW, based on that schematic, you have a variable-magnet alternator (same as in cars), and the regulator applies power to the magnet coils in the rotor via the striped wire shown. Because the rotor is spinning, there is a brush between it and that wire; the high resistance could mean that brush is bad or, it could mean the coils are going bad. The only way to verify and fix either is to remove the rotor.
 

·
Registered
Joined
·
29 Posts
Discussion Starter #6
So I took it to a shop called Obsession Motorsports in Gaithersburg and they replaced the reg/rectifier and sent the stator off to get rebuilt at Ricks. That seems to have fixed my problem. They lost a couple of parts and did a couple of things poorly, but nothing too horrible. I needed to replace the battery because the rectifier was probably the ultimate problem and AC was getting to the battery and cooked it. It would take a charge, but when I tested the voltage, as I was testing it, the voltage kept dropping.

With the new battery, it's now back on the road and seems to be charging the battery just fine.

I wasn't too happy to dump $600 into a bike I paid $650 for, but I think I'm still OK, even with the Mikuni carb upgrade, I'm still under $2,000 into the bike.
 

·
Save them all!
Joined
·
4,278 Posts
No, it's really not. At least you got it fixed and can ride it now, hopefully trouble free!
 

·
ZAMM Fanatic
Joined
·
2,732 Posts
Quick and dirty test of the actual stator output, unplug the main connector there and test the AC voltage with the engine running between the three pairs of yellow wires. You should get something fairly high.
NEVER unplug an alternator / stator while the engine is running.

Unless you like buying parts.

Unplug it THEN start it up.

>They lost a couple of parts

Order/buy the parts, and take them the bill. Otherwise they'll do it to the next guy, too. I 'effin hate careless, sloppy shops / techs.
 
1 - 10 of 10 Posts
Top