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Old 07-22-2013, 05:17 AM   #1
stucknarut OP
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Joined: Dec 2011
Location: Central NC
Oddometer: 157
R90, weird noise and gen light on

Not my bike, but a buddy just had a problem this weekend and I'm going over to look at it tonight. He was at the end of a long ride, and hit a false neutral between 2nd and 3rd and redlined it briefly, problem started then. The bike starts and runs but is making a "weird noise" which sounds like it's coming from the center of the bike and follows RPM, and the gen light stays on. On the chance he burned up a valve, he pulled the valve covers and did a compression check, says it looks normal. Bad rotor maybe? Could a bad rotor make noise?
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Old 07-22-2013, 05:48 AM   #2
Stan_R80/7
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The rotor would be my prime suspect. Good luck!
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Old 07-22-2013, 05:57 AM   #3
bpeckm
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Harsh noise?
Soft noise?
Squealing... grinding....rumbling....lotsa kindsa noises!!

Might be the brushes that jumped/jammed... redline shouldn't bother much of anything... I would pull the front cover (disconnect battery first!) and take a look. Bike can be started with cover off, maybe you can trace that way?

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Old 07-22-2013, 06:33 AM   #4
stucknarut OP
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Haven't heard the noise yet, his description was just 'weird'. Did some more forum searches and found a thread on brushes squealing, that sounds like a good candidate to look at next.
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Old 07-22-2013, 07:32 AM   #5
disston
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I would check the rotor and it's bolt holding it on the end of the crankshaft before running that engine any more. It sounds to me like the rotor was not tight enough and is now actually loose. This will destroy the mating surface of the two. They are a taper fit and precisely matched. Replacing the rotor is easy enough but of course replacing the crankshaft is not that easy.

If it has slipped it may appear tight to cursory investigation. Take the alternator apart and remove the rotor to check they are in good condition.

I forget the actual torque figure called for the alternator bolt but I make mine tight enough to turn the engine over several times. I think this is less than called for in the book but seems to be tight enough. A Noob putting this on or anybody that leaves it finger tight is asking for trouble.

The rotation direction of the crank tends to tighten the rotor but if not made tight enough to begin with it can spin.

Another problem can be caused by putting these things together with out proper cleaning. A taper fitting has to be clean in order to work.
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Old 07-22-2013, 01:25 PM   #6
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I like Disston's ^ possibility... they are a taper, without any keyway, and depend on a tight/friction fit.

Be sure to use a hardened bolt to pull the rotor (if it so loose that it turns, that may not be necessary, but don't take the chance of that bolt snapping off!)

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Old 07-22-2013, 02:02 PM   #7
disston
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We had one of those improperly pulled rotor stories here only several months ago. If you don't have the correct tool to pull the rotor it can be done with a "Hardened" drill bit shank or other improvised tool. Failure to heed this warning will ruin your day.



The tool to pull the rotor^ Same thread as the bolt holding it on but has a long shank to bottom in the crank and force the rotor off. Use of any soft metal in this application traps the piece of metal in the bottom of the crank bored hole and ruins the crank.
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Old 07-22-2013, 04:24 PM   #8
Warin
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The gen light on ... indicates a fault. Not the usual rotor open fault (that is indicated by the gen light NOT coming on at start up). I'd start with this fault .. it may be related to the noise. It does indicate that the alternator output is low, so the bike will stop soon due to a flat battery, put a charger on the battery as a preventative measure while you figure out what is wrong. I too would 'look at' the brushes ..
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Old 07-23-2013, 06:57 AM   #9
stucknarut OP
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Ok, more info. Rattling noise, quite loud, seemed like it was quiet until about 1400 rpm. Sounds like in the center front of the motor. We pulled the front cover and went over the rotor and alternator. Brushes look almost new with good continuity. Slip rings are just a bit worn but not bad. We removed the alternator, only thing there was it looked pretty worn and was loose once removed (copper ring not fitting tightly in the cover). Think it's a press-fit between the case and the cover but maybe one of you guys can tell me for sure. Rotor bolt was snug and it took some force to pop loose of the taper. We took the timing cover off while we were there, timing chain and tensioner both snug.

Going to try swapping an alternator and rotor from my spare bike just to see what happens. What else is there? Only other thing I can think of is a bad con rod, really hoping it's not that. Anyone know an easy way to tell that without pulling the cylinders?
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