B33 mystery Ratteling noise

[WayneBergman]

I am having a heck of a time trying to find the source of a very annoying ratteling coming from what sounds to be the front area of my bike. The sound is what you might expect from two empty spray paint cans beeing shaken violently as fast as you could.

At first I thought it was something bad and serious comming from the motor but no offending sounds when the bike is at idle or under revs when stationary. The sound only happens when the bike is say at around 2500 rpm's and higher  and also the bike has to be moving. Higher the revs the bigger the noise but like I say only when the bike is moving.

Every time I think I have found the source of the noise by just looking the bike over and trying differnt things a road test at higher revs brings me back to square one. Things I have thought were the problem and are not....
1. Silencer touching the frame close to the rear plunger shock.
2. Headlight bulb assembly
3. The fender itself vibrating and touching the forks, one side is very close to the fork legs and I was sure this was it but wedging a piece of leather between the fork leg and fender still gave me the noise.
4.Rear kickstand vibrating on the silencer.

I am almost thinking of taking the fork legs apart and looking inside the legs to see if anything weird going on inside there, not sure if anything in there could rattle around or not. The rebound dampening is not really working properly I know as I get the fork topping out on rebound with clunking sound when riding over pot holes on the road so the forks could use a once over for sure.

Any ideas out there much appreciated, I have been riding it like this now for the 6 months I have owned it. With getting other bugs out of a new ride, at one time this seemed like the least of my problems - but now that the bike is running, handling well and looking like I want it to, I now want to sort out this noise issue.
Thanks very much for any tips if anyone has any ideas..........wayne

[Willie Dee]

Had a similar noise and it was the front mudguard which had cracked behind the fork legs.

[Pete C]

how about the 2 "ears" at the front of the tank? They are not always a close fit to the headstock and I try and fit a thin rubber grommet here to stop the tank rattling about and protect it from (a bit of) the vibes.

The forks don't have a lot insode them and topping out is not unusual. You can get a 2-way damper here http://www.norbsa02.freeuk.com/goffyfork.htm
but if you have access to a lathe you can knock up a set for next to nothing (I can send you the instructions if you want).

[DAVE BRADY]

Hi,

I second Pete C re the front tank mounting.  This has to be very tight.  This problem occurred on my wife's '51 Flash and it needed just another turn on the bolt to get it really tight and the noise stopped - no rubber grommet.  These early tanks must have had vibration issues as they soon became rubber mounted.  It is also important to fit the brace underneath to stop the tank tying to 'flap'.

Dave.

[Rog1]

I get an intermittent vibrating noise from the front of my M33. It doesn't occur most of the time but then I'll get the noise for a few miles and it seems to be sort of engine speed related. When I found a crack in my front mudguard I thought I'd found the cause, but I was wrong. I have no idea what causes the noise but I've worked on most of the front end at one time or another and no damage seems to have been done.

[Jim S]

I had a similar problem with my B33 fuel tank for several years.

To address the problem at the front mount I have a rubber sleeve (rubber hose) over the fixing bolt and I drilled out the holes in the tank so the sleeve passes through. I also made rubber bushings and washers to eliminate any tank to frame metal contact. My fixing bolt is actually a stud threaded both ends and the rubber bushings are sandwiched between large washers on each side of the tank.

At the rear of the tank I basically used the parts book configuration, ensuring there is no metal to metal contact, however the rear bolts are only hand tight and lockwired so they don't fall out. I can slightly rock the tank by hand with this arrangement.

I also originally had a 46 tooth rear sprocket which I changed for a 42 tooth. The 42 tooth is standard. This results in a 9% reduction in engine speed. Maybe since the bike is reving lower it isn't coming close to the tank resonance?

I no longer have the anoying tank buzzing.

[idie]

A lot of the time the noise is the tank making contact with the frame at some point.

[WayneBergman]

Thanks a bunch guys, it was if fact the tank that was making the noise. I put in extra rubber spacers and washers and what not and we are good.
I was reluctant to post this inquiry originally as I figured it would be hard for someone to guess as to what may be causing the noise but glad I did. ...........wayne

[Rog1]

A lot of the time the noise is the tank making contact with the frame at some point.

That suggests that the sound I get is from the tank too, and as it doesn't happen all the time I wonder if it depends on the fuel level.

[B Murphy]

Yes, my tank noise gets louder as the fuel level gets lower. Doesn't bother me anymore you kind of get used to it, also indicates when I need to top it up.

[idie]

I found that when I had the rattling noise on my B33 it happened when the fuel level got low. I think that when the tank is part empty it can resonate and touch the frame.