Honda cb900c fall/charging&running problem

I hope someone can give me some advice about this.

My 1982 Honda cb900 custom fell over on its right side last week. Not a
bad fall, just tipped over while it was running in neutral. After
picking it up, the battery was dead, which was odd because the battery
had given me no trouble before. Gave it a jump (noticed no fluid spill
from the battery) and drove it 2 miles to home. It started up 2 days
later and I drove it about 15 miles and parked it for 4 hours, and then
it wouldn't start up, battery dead again.

I added distilled water to the battery and charged it up for a few
hours. Then I drove it to my mechanic buddy's house, about 20 miles
away. I noticed during the trip that when I revved it up to about
6000rpm or more it seemed like a cylinder was cutting out/ran rough.

My friend tested the charging system and found its not working right.
He's not familiar with this bike and his guess about the charging
system is it's possibly the rectifier causing trouble but more likely
the alternator.

Any advice on how to test for the true problem part here? And would it
cause trouble in the higher rpm as I drove? I'd also appreciate any
hints/tips on disassembly/assembly if there are any when it comes to
the alternator.

Thanks!

 

I suggest removing the battery and getting it load-tested. If the
battery is more than 5 years old, just replace it. I know that they can
last longer, but I just can't be bothered to deal with it long-distance
;-)

Why suspect the alternator instead of the RR?

Here's an oft-recommended fault-finding diagram:
http://electrosport.com/electrosport_fault_finding.html

--
Later,
John



'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.

 

I have yet to find a good explaination of how alternators work. Personally
I know how they work and why they work but sometime it is easier to explain
to someone else is easier with pictures and simple theory.

I haven't seen anyone really show how the alternating magnetic field is
generated in the rotor and what the purpose of the stator is.

The truth of the matter is that the magnetic field does not change in the
rotor. It is the metal of the "clamshells" that allow the magnetic field
appear to change as it is rotated. The clamshells block the magnetic field
except for where there is a gap. Less often explained is the concept of
voltage being created by the movement of a magnet near a coil of wire.
Without these two facts, the alternator is just a mystery machine. In
addition I have even seen many explaination be just plain wrong.

With regards to your 900c charging system, the first thing I would check is
the wiring and connectors. After that I would check the alternator
brushes. It is possible that they are just worn out. The brushes on my 81
Honda last about 30,000 miles. Check the various boards/forums for hints
on how to determine if your brushes are worn out.

BTW, the fall had nothing to do with the failure of the charging system.
The charging system failed the day or days before it fell over. Sort of
like changing a flat tire on your car and then the next day your coffee
maker starts leaking. The two events are unrelated.

How to get at the brushes? They are inside the alternator. You might as
well change the bearings as long as you are in there. I have fixed
alternators just by replacing the bearings. The vibration from the
bearings disrupts the magnetic field being generated by the rotor. All of
this isn't all that hard, just time consuming.

rj

 

Thanks for the replies. Why does my pal suspect the alternator first?
Not sure, he didn't explain his reasoning. Maybe because that's what
side it fell over on. Thanks for the link on the electrical system
check, too.

I'll also let him know about the brushes and bearings while he's
checking it out. I'm still wondering: will fixing the charging problem
also fix the engine sputter I noticed at higher rpms?

 

I am not sure why he suspects the alternator first. Given the nature of
things, I would check it first too. Easy and quick to test provided you
can find the rotor connections.

If the battery is only presenting 10 volts instead of roughly 14 that the
ignition system is looking for, it is a pretty safe bet that the spark will
be weak too.

BTW be prepared to spend an insane amount of money for the brushes if you
order them from Honda. The brushes for my Honda cost about $18.00 each.
Two are required. The fact of the matter is that they should cost no more
than $5 dollars each and even at that I would call that full list price.
Someone is getting very wealthy suppling alternator brushes to Honda.

rj

 

My guess is that it's the battery.

There's not much in the electrical system that's prone to damage in
the kind of "fall" you describe. Not impossible, of course, but IMHO
unlikely.

When you consider how a battery works, it makes perfect sense.

Batteries work with lead plates suspended in acid. Byproducts from
this process build up on the plates, and slough off. That's why the
plates don't extend to the bottom of the battery. That extra room at
the bottom of the battery is there to collect the byproducts, which
would otherwise short out the plates of the battery, since they're
conductive.

When you dropped the bike, all the crap in the bottom of the battery
would have been sloshed back up into the plates, effectively shorting
them out. This assumes the battery is more than a few months old, but
fits the scenario you describe very well. And with a battery with
some shorted cells, the charging system may indeed work less
efficiently (after all, an alternator needs a certain number of volts
to produce rated output - and the shorted battery might prevent this).

Mark Hickey

 

Thanks for the responses. I'll follow up later when we determine the
exact problem.

 

Just wanted to follow up. In short, it's fixed.

When my pal and I took off the cover we found what seemed to be bits
from the stator in the bottom of the compartment. I'd guess that the
inital fall thumped the side well enough to cause some damage, maybe
wedge some of the bits between the rotor and stator.

After checking the brushes for wear and doing the tests from the Honda
manual on the big three (reg/rect., rotor and stator) the stator did
seem to be the likely culprit.

I ordered a new stator and cover gasket from Rick's Motorsport
Electrics ($162 including 2nd day shipping) and we put it in last
night. No fun pulling the old wire loom out, either.

Now it's charging again. Only secondary problem we had was in checking
connections we caused a weak connection at pulser coupler B causing 2
cylinders not to fire. We think it's working now but I'll at least know
if the bike loses power where to look first.