Knocking sound on 99FI

[Alexhoc]

I got home tonight and I could hear a knocking sound from the bike. Thankfully this started happening about 400 yards from home so I rode it back.

The sound seems to be coming from the gearbox area, and could be described as a bike chain rubbing against the edge of a metal casing. Only my chain isn't rubbing (I don't think) and the sound goes away under acceleration.

The bike still rides fine, gears are fine, and it's not displayed any signs of any impending doom, until now.

I'm going to go and investigate (once it stops raining), but in the meantime, what could it be?

This is a serious thread, but bonus points to the person who gets closest to the final answer once I've found out the cause.

I'm booked to go to the TT in 2 weeks, so I really hope it's not anything bad!

 

[derek kelly]

Run the bike on idle & pull your clutch lever, if it stops then it's the clutch basket rattle, nowt to worry about.

 

[Alexhoc]

Feels more of a solid sound than a rattle if you know what I mean.

It does it regardless of the clutch position, and is directly related to the speed of the wheel.

I have been looking at it since I got back, and as the bike cooled the noise disappeared. I've had the front sprocket cover off and it's not in there.

 

[Centaur]

Perhaps the old favourite.

If it is rattling at 3/4K it could be the cct. What is the mileage, Alex?

 

[Alexhoc]

Mileage is about 45k, I changed the cct about 2000 miles ago, probably less.

One thing I've not made clear, the noise is there even with the engine off, just spinning the back wheel by hand...

 

[noobie]

Is the chain correctly adjusted?

 

[Alexhoc]

Yes as far as I can tell, it's got the correct amount of play. Not sure how "loose" the play is supposed to be though.

 

[DEG5Y]

Wheel bearing?

Sprocket or disc bolt worked loose catching on something as it turns?

 

[andyBeaker]

Wheel bearing?

Sprocket or disc bolt worked loose catching on something as it turns?

Boom.

Sounds most likely to me. I had two bearings fail on different Bird sprocket holders.Even if it is the wheel bearings it is an easy DIY job.

 

[Alexhoc]

OK, I checked this morning and there is nothing catching the swingarm. There is no noticeable resistance from the wheel when the noise happens either. I will take the chain off next week and see if it makes any difference.

There are still a few points at the back of my mind though:

• Why would this noise disappear as the bike cools?
• When listening to it (engine off, bike on centre stand), it really sounds as though it's coming from the engine. But when listening with a stick, the noise is the same (or very similar) from the engine casing or from the wheel spindle.
• There is no noticeable effect on how the bike rides and goes through the gears, surely if it was a gearbox/clutch issue I'd feel it?

The sound can be described as a light tap against a hollow alloy container, its frequency goes up as the wheel spins faster.

 

[Centaur]

Yes as far as I can tell, it's got the correct amount of play. Not sure how "loose" the play is supposed to be though.

Did you check the play with someone of your weight sitting on the bike to compress the rear end. Alex?

Another thought; Can you spin the rear wheel with the chain off?

 

[DEG5Y]

Doing the same speed but in different gears does this alter the frequency?

No - wheel
Yes - engine

 

[Centaur]

Doing the same speed but in different gears does this alter the frequency?

No - wheel
Yes - engine

See post #3, DEG5Y. Related to wheel speed. gr0n: :-0)

 

[andyBeaker]

OK, I checked this morning and there is nothing catching the swingarm. There is no noticeable resistance from the wheel when the noise happens either. I will take the chain off next week and see if it makes any difference.

There are still a few points at the back of my mind though:

• Why would this noise disappear as the bike cools?
• When listening to it (engine off, bike on centre stand), it really sounds as though it's coming from the engine. But when listening with a stick, the noise is the same (or very similar) from the engine casing or from the wheel spindle.
• There is no noticeable effect on how the bike rides and goes through the gears, surely if it was a gearbox/clutch issue I'd feel it?

The sound can be described as a light tap against a hollow alloy container, its frequency goes up as the wheel spins faster.

Check the rear wheel bearings and the bearing in the sprocket carrier........

 

[ianrobbo1]

Make sure the brake caliper holder "the alloy bit on the off side" is seated correctly and nothing is stuck in the caliper itself, let us know what it was when you sort it please??

 

[Alexhoc]

I will take the wheel off one evening next week and have a good poke around. Unfortunately I'm away all weekend so I can't spend time on it, but I will let you know if I find out.

 

[Jaws]

The only obvious ones that spring to mind are, as mentioned, wheel bearings or cush drive rubbers or indeed the bearing in the sprocket carrier.. or ( and it would not explain why it tends to go away when warm ) the rubber has gone missing off the left hand zorst can and the chain is sometimes catching on the centre stand

 

[noobie]

Does it make a noise like this ?

https://www.youtube.com/watch?v=Wv4LYVYM1ik

 

[Alexhoc]

It could be a similar sound noobie, but it's consistant as the wheel spins, and high frequency.

However, I've checked the chain and wheel area tonight and found the chain was a little tight, and also the wheel wasn't straight. No idea how I managed to mess this up last time, but as I slackened the left hand side, measured the distance to the axle, then measured the right hand side I found I had to actually pull it back on that side. The wheel turns a lot more easily now.

I'll keep and eye on it and let you know if the noise comes back, unfortunately I'm not often getting a chance to ride the bike long enough to warm it up properly at the moment.

 

[Jaws]

hmmm.. If it was MUCH too tight it may have buggered up either the sprocket carrier bearing or even the gearbox output shaft bearing..
Hopefully sorting out the mal-adjustment will be the cure though @tu*