GSX750F banging noise?

**T.W.R** · 12th January 2010, 07:58

Originally Posted by sammcj

I just re-read that post.
It disappears when the clutch is IN, i.e. when you're not in gear

Check the bearing

**sammcj** · 12th January 2010, 08:04

haha this is getting messy, the sound:

IS there when accelerating normally.

If I'm riding down the Street and I can hear the noise, I put my hand in the clutch and the noise goes away even if I rev the bike.

Can you put the bike on its main stand, start the engine, put the bike in first and let the clutch out. Now the wheel is spinning, what do you see/hear? Pull the clutch in and see/hear what happens.

When I get the sprockets on tonight I'll put it on the stand and let you know.

**vifferman** · 12th January 2010, 08:12

Usually, if the noise disappears when you pull the clutch in while moving, then it's not the chain'n'sprockets (good test for that).
Also, you said it's only between 2.5k rpm and 5k - does the bike have a flapper valve in the airbox? If so, disable it and see (hear?) if the sound disappears.

**sammcj** · 12th January 2010, 08:17

Originally Posted by vifferman

Usually, if the noise disappears when you pull the clutch in while moving, then it's not the chain'n'sprockets (good test for that).
Also, you said it's only between 2.5k rpm and 5k - does the bike have a flapper valve in the airbox? If so, disable it and see (hear?) if the sound disappears.

I just googled flapper valve and was greeted with a lovely range toilets

I'll rip the air box out tonight also, will it be pretty obvious what to look for? (I'm guessing something a bit like the flap on a carbie?)

**vifferman** · 12th January 2010, 08:24

Originally Posted by sammcj

I'll rip the air box out tonight also, will it be pretty obvious what to look for? (I'm guessing something a bit like the flap on a carbie?)

If there's a flapper valve, you'll see a metal diaphragm thingo (technical term) somehwere on the airbox, with a rubber tube going into it from the intake manifold, and an arm disappearing into part of the airbox.
It's designed that at low revs it forces the airbox to breathe through a smaller orifice so there's less intake noise. When the throttle's wide open and/or at certain revs (usually around 5- 5.5krpm) above the range they test noise emissions, the flapper valve stays open.
If it has one, pulling the vacuum tube off (and plugging the end of the hose so your bike doesn't run lean!) will disable it and mean the flapper's open all the time.

**Squiggles** · 12th January 2010, 08:27

Put it on the stand and try to identify where its actually coming from... Work from there

**vifferman** · 12th January 2010, 08:28

Originally Posted by Squiggles

Put it on the stand and try to identify where its actually coming from... Work from there

That's a good idea. Be aware though that with the bike in gear and no load on the rear wheel, there'll be a lot more flapping around of the chain than normal.

**sammcj** · 12th January 2010, 08:34

Put it on the stand and try to identify where its actually coming from... Work from there

1st priority as soon as sprockets are on.
2nd is check engine mounts and airbox 'flapper valve'

**sammcj** · 12th January 2010, 09:17

Spoke with sportzones mechanic, he thinks it could be the clutch plate / cover.
He seemed to think that if it was the gb baring or shaft I'd know about it.

**avgas** · 12th January 2010, 09:43

take all the plastics off and go for a ride and see if it still exists. I had a similar problem and all it was 1 of the fairings 'tapping' the frame at certain revs. Solved with a small bit of rubber.

**MSTRS:Me** · 12th January 2010, 09:51

Originally Posted by sammcj

Spoke with sportzones mechanic, he thinks it could be the clutch plate / cover.

There's 2. One on the right, has the oil filler and level window in it ...which would heamorrage oil if it was 'loose'. And one on the left where the actuator mechanism is located (also doubles as the front sprocket cover)...just check/tighten the 5? allen head bolts holding it on. But I doubt that'd be the source.

**sammcj** · 12th January 2010, 09:59

Already have the LHS one to do the sprocket, bolts were tight as when I took it off and spring etc all looks fine in there.

So I'd have to drain my oil to do the clutch? (take it thats what a wet clutch is!)

take all the plastics off and go for a ride and see if it still exists. I had a similar problem and all it was 1 of the fairings 'tapping' the frame at certain revs. Solved with a small bit of rubber

Will do.

Funny thing: I could be imagning it but I swear its worst when I lean to the left and quieter when I lean to the right - BUT I haven't riden her enough to say that for certain yet.
I now have a power bar so the sprocket change should go ahead tonight.

**MSTRS:Me** · 12th January 2010, 10:18

Originally Posted by sammcj

Already have the LHS one to do the sprocket, bolts were tight as when I took it off and spring etc all looks fine in there.

So I'd have to drain my oil to do the clutch? (take it thats what a wet clutch is!)

Will do.

Funny thing: I could be imagning it but I swear its worst when I lean to the left and quieter when I lean to the right - BUT I haven't riden her enough to say that for certain yet.
I now have a power bar so the sprocket change should go ahead tonight.

That is probably your head moving to that side of the bike when you turn..meaning that a turn to the left suggests that the source of the noise is on the left. It brings us back to chain, sprockets or final drive bearing