Graunchy Sound Under Low Acceleration

Good evening all,

I appear to have a bit of a gremlin lurking somewhere in my bike, under low acceleration I get a graunchy sensation/sound coming from the bike.

I've had a dig around and checked for any rattles that might have caused it, replaced a few hose clamps, checked my forks, shock, both wheel bearings, brake pads ( almost sounds like very soft metal on metal ) and anything else I could think of external to the bikes engine but to no avail.

There's no lack or loss of power from the engine, at all other revs it runs as smoothly as usual, but at low rpm under gentle acceleration in any gear I get a little graunchy noise and it's driving me nuts.

My assumption would be that it's the clutch or transmission, but before I make a potentially expensive trip to the garage I'd like to know if anyone has any other bright ideas.

Peace,

Liam

EDIT: Also checked chain, sprockets and all fluid levels.

[Craig380]

When you say low rpm, how low do you mean - 2,000rpm? 3,000rpm? Is the bike standard, i.e. factory airbox with intake snorkel, air filter, factory exhaust etc?

Does it carry on making the same noise if you pull the clutch lever while rolling at speed? How about if you accelerate gently in second gear then knock it into neutral and carry on rolling in neutral, does the noise stop or continue?

Bike is standard apart from some cosmetic changes ( levers, bar ends ) an oil drip for the chain and a GPS tracker.

It kicks in just above idle, so around 1.2k and seems to stop above 2k RPM, it's just that small range but seems to be in every gear. It doesn't occur if I gently pull in the clutch while rolling at speed, and doesn't happen in neutral at all which is what led me to think it may be the transmission or clutch after eliminating the other potential sources :/

EDIT: Corrected spelling error.

[Teejayexc]

Sprocket bearing, chain got a tight spot, front sprocket ok?

*sigh*

I think I may have found the cause, thank god I work in part with a steel fabricators.



I think it's safe to say that clamp and section of exhaust has seen better days, yes?

I'll get that rust blasted and the crack welded over the next few days and see if that stops the sound and get a new header ordered as I'll need to do it regardless looking at that.

EDIT:

@Teejayexc Yeah, the sprockets ( front and rear ), are pretty much new as I replaced them when I got the bike along with the chain, the bearing was replaced by previous owner about a year ago ( full service history with stamps etc ) though I haven't physically checked the bearing myself yet.

Looks like image won't load, http://imgur.com/a/BDJD1 ( I've also whacked it in my album )

[Blapper]

LOL! That would do it OK! Glad to read you found it.

On a side note, I would avoid those ultra low revs if I were you.

[Craig380]

Yes, that crack would explain it ...

As Blapper said, I also prefer to avoid riding below 2K rpm for any length of time unless it's trickling in traffic in 1st gear ...

[R1ffR4ff]

Originally Posted by Blapper

LOL! That would do it OK! Glad to read you found it.

On a side note, I would avoid those ultra low revs if I were you.

+10

Hehe,

Managed to convince someone on site to weld it up when they get some free time, so should be done today or tomorrow.

And yeah, it's that bloody slow trickle traffic in roads too narrow to filter / too busy and blind to overtake that led me to notice it.

EDIT: Now I just have to hope it gets rid of the graunchy noise when it's done, or I would have found two problems I need to fix!

[Biker Biggles]

Hopefully its sorted but---------
You say it had a new output shaft bearing last year and its had new chain and sprockets.Why did that bearing fail?You dont state the mileage but its not a common problem unless the chain was run too tight.If the issue persists Id look hard at that area.