Help with my clunk - Gsx750

[Kayak23]

I’ve recently started to get this weird rhythmic clunk or crusty slap for want of a better description on my 2000 gsx750 Inazuma.

It happens mostly seemingly when I’ve slowed down for a junction or something and then I’m accelerating up again.

Seems to disappear at higher revs where the engine runs smoothly, but building up to speed I can hear a clunk and even feel it a bit through the pegs.

It seems to happen in any gear and only when under load. The second I shut the throttle or pull the clutch it disappears.
It may well be there a little at higher speeds but maybe it's just I can't hear it.

I’ve checked everything I can think of and can check easily.

Chain tension, chain movement (removed it and checked all the links move ok), checked sprocket bolt is tight, rear sprocket is tight, chain sliders on swingarm are all running good, sprockets don’t seem worn at all, no chips or bent teeth.

Anyone got any ideas what to check next?

The fact that it's only there under power is maybe more telling.
If the chain was bad it would still do it after I pull the clutch I guess but it doesn't.

I even took it to the bike shop today, the mechanic went up the road on it and he couldn't figure it out.
I've got it booked in for a deeper look but it would be cool if I could diagnose it before.
Any ideas anyone?
Cheers.

[xX-Alex-Xx]

What’s it rhythmic with? Directly related to Speed, engine speed, something else? What’s the state of the chain and sprockets, especially the teeth on the sprocket?
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DILLIGAF

[Kayak23]

It's rhythmic with road speed I guess. I can hear it increasing in frequency as I speed up, but then either it goes, or I just can't hear it over the wind and engine noise.

Seems to happen in any gear.

I thought originally maybe a stone in the rotor or something like that but I've checked all that several times.

The chain and sprockets are pretty good. I took the chain off and tried all the links which seem to all be fine. Both sprockets are good too. I even said to the garage bloke should I replace them just to rule it out but he thought they looked in good condition with correct tension etc.

I was thinking the chain was ruled out due to the fact that the noise stops as soon as I pull the clutch or as soon as I ease off the throttle (and I'm only talking about gentle acceleration anyway, although it makes the sound under hard acceleration too).

[jaffa90]

Have you a paddock stand so you can rotate the small sprocket shaft in neutral and watch for a sprocket tooth lifting the chain rather than pulling it.?

[Kayak23]

Yeah, tried that. It all seems to run smooth.
The chain jumps about a bit with the engine running up on the stand but you expect a bit of that with the wheel off the ground.

[wr6133]

Stethoscope real or homemade. Try to locate the actual sound, can then narrow down where to look.

Does the sound go away when hot?

100% its not there at idle?

Is it laying down power as it should or is the clutch slipping?

Mileage, servicing?

[Kayak23]

I'll try a stethoscope (screwdriver handle in me earhole)

It doesn't disappear when hot, makes no difference.

It's not there at idle, just when pulling up to speed in any gear.

Laying down power beautifully. Really smooth and powerful. Just makes a funny noise.

It's average mileage and I changed oil and filters nearly a year ago but only really ride it once a week maybe.

[xX-Alex-Xx]

Does it make the noise when revving up hard from idle on the driveway?
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DILLIGAF

[Kayak23]

Only in gear. Doesn't make any clicky noise when not moving.

Thanks for your continued help by the way 😐👍

[xX-Alex-Xx]

All I can think of is something gearbox related (I'm sure someone else will say otherwise though !!). Would be nice to have a dyno so you can get the thing under load without it going anywhere ....
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DILLIGAF

[wr6133]

Probably not valves or worn out clutch plates then.

My next thought would be pulling the gearbox apart, though hopefully someone with more brains than me is going to give you a better answer than that

[jaffa90]

You need ear plugs!
Engine mountings?
Never experience this but if it was my bike i would remove the oil filter and split it open.

[pepperami]

Cush drive rubbers worn?
Every time you excelerate = clunk?
Every time you roll off the throttle = clunk?


Just an idea?
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I am the sum total of my own existence, what went before makes me who I am now!

[Bru]

Good point on the cush rubbers.

Would a failing sprocket bearing have a similar effect, in that the sprocket can shift a bit under load and load the chain laterally? I've never experienced this myself, but if the noise is audible over/through the engine under load and linked to road speed, then it does suggest a drivetrain issue.

[Kayak23]

Cheers folks. I'm praying it's not gearbox related.
Good call on the oil filter. I'll check that and the cush drive this week.

[jaffa90]

If no metal inside the oil filter then i would feel the back wheel bearings for heat after a run.

[Irezumi]

Highly unlikely and a bit of a long shot but I had similar once. Went to have a look at front wheel bearings and saw a piece of duck tape with some gravel attached to the inside of the front mudguard. Removed and noise/problem was solved.

As said unlikely but worth a check.

[Kayak23]

I don't actually have a front mud guard on just now but it's a good point. I'll check around everywhere! 😂

[Nobby the Bastard]

Have you tried to pull the chain away from the rear sprocket about half way up the sprocket?

The last time I had a noise like this it was with what seemed a good chain and sprocket but it was so worn the chain links could be pulled about 1/4 inch from the sprocket and was clearly badly worn.

This is the downside of a scotoiler.....
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[Kayak23]

Yeah the chain is all good. Even the mechanic who had a quick look said so. I suggested I change it just to rule it out but he reckoned it was good and well adjusted.

[Kayak23]

Well it's not the cush drive. Looks in very good condition.
As soon as I put it in gear with the rear wheel jacked up it does this occasional jolt or clunk.
Weird.
See what the bike shop say when they have a better look on Monday.

[martin734]

Not too familiar with that bike, but is it possible to run the bike in gear on a paddock stand with the front sprocket cover off? If so it may be possible to see what is happening when it jolts or clunks.
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Current bike: ST1100 "Big Red"

[Kayak23]

Yeah. I've put a video on YouTube of it. The chain sort of slaps about a bit but I'd expect a bit of that with no load or tension in the chain what with the wheel off the ground.
Can't see the sprocket doing anything unusual though.

https://youtu.be/V83HZEBIkAU


https://youtu.be/Q5HqryOkyfo

When it does clunk, it's not rhythmic suggesting a stiff link or anything in a set place per rotation, and as I say, when riding it on the road it only makes a noise during acceleration. Pulling the clutch in or shutting the throttle stops the noise.

[Nobby the Bastard]

Sorry but that chain doesnt look very healthy to me.

The reason why the noise disappears is because when you pull the clutch or back off.all the slack moves to the top of the run rather than the bottom.

You need a new chain and sprockets.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[Kayak23]

Well, just to update this.
All those that said I needed a new chain and sprockets, well done. Seems you were right.

I was all about ready to get it booked into the bike shop to get the gearbox cracked open and get a rebuild. That was going to cost a lot of dough.

Despite the bike shop saying that my chain and sprockets were absolutely fine, I decided sod it, I'll change them anyway just to be absolutely sure.

Well, the noise has gone!

I've got a new noise though 😂 On deceleration, the engine now whirrs a bit, like an airplane coming in to land. It's after the shop took the clutch out and back in to do some checks.

Oh well, at least the original noise has gone and it seems to run well.

Thanks to all who helped 👊