Author Topic: CB400F - Melted wiring  (Read 977 times)

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Offline The Lone Builder

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CB400F - Melted wiring
« on: June 28, 2018, 05:07:00 AM »
I recently acquired a CB400F for restoration. It started after sitting for 18 years.

One thing that was u/s was the solenoid. I opend this up and cleaned it. It seems to be working now - time will tell.

In the process I noted the red/white wire from rectifier to solenoid was melted - and only the red/white wire. All yellow wires are fine and the red from solenoid to battery is fine.

I checked the rectifier and 2/3 sectors are fried.  I have not been able to test alternator or regulator. The main fuse had been bypassed by a pretty thick external wire. As suggested in the pics, the connections were in a bad state, especially the red/white, which was bottom right in the last pic.

What would cause the red/white wire to melt like this - actually it is only the plastic that's melted; the wire itself is OK?

Sean
CB750 K2 - From Belfast-2-Belfast
CB750 K1 - The less, said the better!
CB450 K1 - Stalled.
CB400F Supersport - Not Rusty any more!

Follow my journey through Africa @ http://Belfast2BelfastByBike.com

Offline TwoTired

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Re: CB400F - Melted wiring
« Reply #1 on: June 28, 2018, 11:25:08 AM »
The insulation melts when the wire gets too hot, and that is usually from pulling more current.  The red/wht wire is only half the current pathway.  Current needs to return to battery in some way and that is usually the Green wire path.  Check all the ground connections and wires.

Overcurrent can be caused by a faulty rectifier, or (even Momentarily) reversing the battery leads, turning all the rectifier diodes fully into conduction.

Of course, with the fuse by passed, overcurrent will seek out the weakest pathway to turn into a fusible link.   Let's see, by pass the fuse, short the wiring someplace on the bike and ... poof.

And, the wire itself may not be ok.  Multistrands, can melt or part only some strands.  Can't really tell without looking at them all.  They can part at the crimp connections, too, leaving less strands to carry the current loads.

Cheers,

Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline The Lone Builder

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Re: CB400F - Melted wiring
« Reply #2 on: June 28, 2018, 01:17:45 PM »
Hi TT,

Since I've no real idea of the history of the bike, it could be any of those.

In particular, at one of the crimps - I forget which - some of the strands were broken. The green looks OK as far as I've looked at it.

Further work on the project wil be limited and delayed as I head back to Harare on Monday. One job I have clearly added to the task list is to overhaul the harness and replace the rectifier and regulator with a solid state affair.

Whilst on teh topic, do you know why the bike has a separate diode outside the rectifier?

Sad I couldn't get it running before, but there you go.

Sean
CB750 K2 - From Belfast-2-Belfast
CB750 K1 - The less, said the better!
CB450 K1 - Stalled.
CB400F Supersport - Not Rusty any more!

Follow my journey through Africa @ http://Belfast2BelfastByBike.com

Offline Bodi

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Re: CB400F - Melted wiring
« Reply #3 on: June 28, 2018, 02:01:22 PM »
The extra diode is for the starter interlock, so you can't start the bike in gear with the clutch engaged.
Definitely a super bad idea to bypass the main fuse.

Offline The Lone Builder

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Re: CB400F - Melted wiring
« Reply #4 on: June 28, 2018, 03:53:30 PM »
Thanks for info.

Can't argue with the bypass daftness!

Sean
CB750 K2 - From Belfast-2-Belfast
CB750 K1 - The less, said the better!
CB450 K1 - Stalled.
CB400F Supersport - Not Rusty any more!

Follow my journey through Africa @ http://Belfast2BelfastByBike.com

Offline TwoTired

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Re: CB400F - Melted wiring
« Reply #5 on: June 28, 2018, 08:46:18 PM »
The stock bike allowed the electric start to be used either in neutral or with the clutch pulled in.  In neutral, the nuetral light comes on.  The single diode kept the neutral light from coming on when the clutch was pulled in.

If you are asking why there is a separate rectifier and regulator for the stock bike, it was an evolutionary affair.  The stock regulator wasn't electronic, being more of a tuned relay type affair with contacts to control the Alternator field current.  And early models had a selenium rectifier which evolved into a six diode block.  Their is nothing wrong with the stock units (except the selenium rectifier which becomes rather unreliable).  I still use the stock regulator and rectifiers in all my bikes, and surprise, they still function like they did when new.   Not everything "modern" is actually better.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline The Lone Builder

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Re: CB400F - Melted wiring
« Reply #6 on: June 30, 2018, 03:42:25 AM »
No, I was looking for an explanation for the separate diode.

I, too, would be quite happy to keep using the original rectifier, but as I said, two of the circuits - if that's the right word - are dead. There's no connection between two of yellows and red/green.

Going home on MOnday, so the bike will be put back into sotrage for a bit, till I get back.
CB750 K2 - From Belfast-2-Belfast
CB750 K1 - The less, said the better!
CB450 K1 - Stalled.
CB400F Supersport - Not Rusty any more!

Follow my journey through Africa @ http://Belfast2BelfastByBike.com

Offline TwoTired

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Re: CB400F - Melted wiring
« Reply #7 on: June 30, 2018, 08:21:28 AM »

I, too, would be quite happy to keep using the original rectifier, but as I said, two of the circuits - if that's the right word - are dead. There's no connection between two of yellows and red/green.

Not clear if your measurements included both polarity probe placements.   It matters.

Cheers.
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.