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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: kris on April 25, 2015, 11:44:47 PM

Title: Rough Noise With Throttle Twist at Idle
Post by: kris on April 25, 2015, 11:44:47 PM

Hi all,
The bike purrs at idle and sounds fine at speed. It is when I pump the throttle (at idle) or during take-off  from a dead stop that I get this rough sounding mechanical noise...not terrible but I'm not comfortable with it. I've been reading some of the articles on monkey nuts. Do worn nuts produce a constant sound or might they be the culprit in this case? The bike has 62,000 miles on her. I will try to post a video clip (with audio) tomorrow to give you a sense of what I'm hearing.

Thanks.

Title: Re: Rough Noise With Throttle Twist at Idle
Post by: RobP on April 26, 2015, 10:09:11 AM

Can you isolate the noise to either the left or right side of the engine?

Title: Re: Rough Noise With Throttle Twist at Idle
Post by: Chaos on April 26, 2015, 10:40:33 AM

could be the alternator cush drive, aka monkey nuts.  Rubber disintegrates, allowing metal on metal contact, most noticeable at or right off idle  (#9 in drawing)

Title: Re: Rough Noise With Throttle Twist at Idle
Post by: kris on April 26, 2015, 12:39:45 PM

Thanks guys. Rob, I will try to do that. My guess would be right side but I'll have a better listen and get some audio posted.

Title: Re: Rough Noise With Throttle Twist at Idle
Post by: K75rt on April 26, 2015, 02:59:21 PM

The monkey nuts are no longer as cheap as they once were, and unless they've improved them, the aftermarket ones are not the greatest.  If yours have turned to mud, and it sounds like they might have, make sure to either have the cup (part#7) on hand or be able to lay up the bike while you get it.  The fins in the cup will chip off if the nutz are really shot, and if you just put new nutz in without replacing the cup they will fail in short order.  Fortunately the cup isn't too expensive.
Edit - $15.83 for the cup and a buck for the washer.

Title: Re: Rough Noise With Throttle Twist at Idle
Post by: kris on April 28, 2015, 08:19:20 AM

Thanks K75RT. I have to dig into soon.

Title: Re: Rough Noise With Throttle Twist at Idle
Post by: kris on April 29, 2015, 08:10:47 AM

So, it ain't the monkey nuts that are the source of the noise. (what a weird name!) Pulled the alternator. The rubber looked pretty good, actually. No damage to the cup. I cleaned everything up and smeared dielectric grease (apparently does not react with rubber) all over the nuts just to keep things loose. I did notice that it looked like some of the nuts had bonded to the cup from heat or rubber degradation. The nuts did have a little bit of mushy rubber in a couple of spots...really minor. I cut that stuff out with a utility blade. The alternator extraction is quite straightforward. Didn't have time (or the interest) to pull the alternator apart to check brushes....next time.

Title: Re: Rough Noise With Throttle Twist at Idle
Post by: rbm on April 29, 2015, 02:48:36 PM

The cush rubbers look slightly worn and MAY contribute to your noise.  Two of the gaps look big (the rubbers should almost touch) and one of the rubbers is installed upsidedown.  Did you try running the engine without the alternator installed to see of the noise abated or remains?

Title: Re: Rough Noise With Throttle Twist at Idle
Post by: kris on April 29, 2015, 03:30:28 PM

I re-installed the nuts correctly. Should have taken a picture of the finished product to complete the thread. Things looked good and seem to run smoothly. Next time in I will try the sans-alternator test. I've got valve clearances to check, TB boots and TBs to sync! Never dull...