Another Noisey Bit Question

[G-Zero]

I had my bike serviced over the summer and the ancient BB replaced with a new one, with new cranks, chain, chain ring & rear cassette etc.

This week I started to notice an occasional sharp metallic crack noise, which I think is coming from the area of the BB or cranks.

I have checked as far as I can and can find nothing loose and everything seems to be rotating freely.

When I'm pedalling there is no noise evident, but if I freewheel for a bit then start to pedal again, I hear this crack as I start to pedal again. It only happens once as I commence pedalling and does not reoccur until I freewheel again. It makes no difference if I push on with the left or right pedal first and is gradually getting louder.

I'm hoping that the bike will last until my new one arrives in December and can't really afford to lose it for even a day as it's needed every day for the commute. The original BB lasted over 12 years, so surely this one can't be on its way out after 6 months.... Can it ?

 

[gbb]

Had the same myself G-Zero,not as bad as yours, but never got a clear idea of exactly what caused it.
It puts me in mind of the balls in the BB clashing against each other, you get the cracking sound as it frees, then its ok.
Mine seemed to clear after a while, can't think its done it for ages now (same BB)

 

[rowan 46]

It may be the pawls on the freehub sticking in which case the hub is on the way out. Did you have new wheels?

 

[Zoiders]

If it's your Scott suspension bike check the swing arm.

The machined web section at the pivot that grips the cartridge bearing has been known to fracture, it's a known problem and Scott did issue a re-call, instead of using a perfectly simple push fit for the bearing with solid metal all around it like a cartridge bearing hub they instead decided to grip it with a split sided eye bolt design like the clamp of a handlebar stem. It creates a stress riser that does not stand up to long term use under the full weight of a rider.

On single pivot suspension arms you get a degree of movement of the swing arm when you pedal as drive force compresses the swing arm, the chain pulling the sprocket around tries to compress the shock you see, when you ease off it extends again, this may explain why it clicks after you freewheel.

Look hard as a crack may only open up when you stress it with movement.

On a related note it could also be the cartridge bearing in the swing arm that has gone and is clicking when it moves, the intermittent clicking being caused by the same pattern of use as mentioned above, they are cheap to replace though, less then a tenner.

 

[G-Zero]

Thanks all for your thoughts on this.

I didn't get new wheels fitted and have noticed that there is a bit of a rumble coming from the freewheel hub, which I'm sure I haven't noticed before. I hadn't considered that the noise could be transferring from the back.

It is the full sus bike, as that's all I've got at the moment

I'm having a maintenance day tomorrow and will have a good look at the swingarm and suspension mounts; and again I hadn't considered that the noise could be transferring through from this area.

Cheers.

 

[G-Zero]

Well I'm no further forward

Gave the bike a good going over at the weekend and the swingarm and suspension seem fine, but I'm no expert.

Think I'm going to have to bite the bullet and get it in to the LBS.

 

[G-Zero]

Turns out the rear hub is FUBAR.

LBS did me a temp fix to keep me going for a couple of weeks until the new bike gets here, then when I can afford the time for them to hang on to my wheel, the're going to drop me a new LX hub in.

 

[albion]

From experience it sounds like my broken rear hub spindle.

I replaced the bearings in mine not noticing I had a crack or maybe even a full break in the spindle causing a corresponding noise on drive takeup. It was only really pressure and the left side holding the wheel on!