Vibration in ZX7R, clues?

[ElCoyote]

I have a vibration that starts at about 3.5K in the footpegs and at 4K moves to handlebars. Very severe at 5K+. Declutching makes it disappear which should help pinpoint what I need to check. Chain brand new and sprockets do not appear worn or hooked. Any help greatly appreciated.

[HDTboy]

Is it in any particular gear?
Are all of the engine mounting bolts tnstalled and tight?
Is it misfiring or otherwise running rough?
Are there any cracks in the frame?
Have you got bar end weights fitted?

[ElCoyote]

Thanks for the reply,

Bike is a recent purchase and I feel engine mounts to be the main possibility due to it being a high frequency vibration. Trying to avoid removing the fairing if at all possible because I am not familiar with the engine mount positions. (Read I have not owned a bike since my 1964 Bonnevile).

Vibrates in any gear at the same rev range

Runs like a sewing machine so not misfiring

Frame cracks........takes a big gulp. Are there any known places to crack on this model?

Bar end weights are are fitted

[HDTboy]

Mate, I'm no expert. I'm just suggesting you check the basics.
Removing the lower fairings is a good place to start.
Is it just a resonant vibration? Maybe it's normal?

[ElCoyote]

Mate, I'm no expert. I'm just suggesting you check the basics.
Removing the lower fairings is a good place to start.
Is it just a resonant vibration? Maybe it's normal?

Being new to modern bikes I cannot say but my gut feeling is that it not normal. This breed of multi-cylinder twins should be as smooth as a billiard ball but apart from the discomfort on a trip I am also seeing dollar signs and a side of the road moment I do not want to contemplate.

I guess I am asking whether this model bike has a common fault or I am just an unlucky bastard.

[HDTboy]

This breed of multi-cylinder twins

Huh?

Pull the fairings off and have a look. If you're not confident in doing so, then pay someone who is. I haven't had any experience with the ZX7, but being a water cooled 4, it should be fairly smooth.

[ElCoyote]

Huh?

Pull the fairings off and have a look. If you're not confident in doing so, then pay someone who is. I haven't had any experience with the ZX7, but being a water cooled 4, it should be fairly smooth.

Many thanks, KB'rs are indeed a special breed.

Happy new year maybe we will meet on a ride someday and I can thank you in person.

[AllanB]

The 4's do tend to have a 'rough' patch somewhere in the rev range usually only a patch or two of about 500rpm, and usually smack where you want to ride! They are so smooth elsewhere that this is more noticeable.

If yours is from 4500 all the way up to the top end then you are correct that something is not 100%.

Grab a beer and settle into the workshop and check all nuts and bolts are tight (fairing removal is easy). Its also a good way to introduce yourself to your new bike (in a perfect world the same procedure would apply to all first dates).

Check the header bolts and all muffler mounts/bolts as well as if they are loose it can send a vibration through the bike.

Good luck.

[ElCoyote]

The 4's do tend to have a 'rough' patch somewhere in the rev range usually only a patch or two of about 500rpm, and usually smack where you want to ride! They are so smooth elsewhere that this is more noticeable.

If yours is from 4500 all the way up to the top end then you are correct that something is not 100%.

Grab a beer and settle into the workshop and check all nuts and bolts are tight (fairing removal is easy). Its also a good way to introduce yourself to your new bike (in a perfect world the same procedure would apply to all first dates).

Check the header bolts and all muffler mounts/bolts as well as if they are loose it can send a vibration through the bike.

Good luck.

Thanks AlanB,

Yes the range is roughly what you mention and I have been loathe to venture past that. I suspect that it does smooth out but my thoughts were if it lets go the damage would be worse at say 8000 rpm. Grabbing a beer is by far the best solution I have had so far and I will follow it to the letter.

[Max Preload]

Does it do it at the same engine speeds in neutral? (watch the mirrors for blur) If so, I would suggest carburettor balance would be a first port of call. Engine mounts would be unlikely as that normally manifests as a single clunk when the engine comes onto load and off again.

[Mole_C]

Does it do it at the same engine speeds in neutral? (watch the mirrors for blur) If so, I would suggest carburettor balance would be a first port of call. Engine mounts would be unlikely as that normally manifests as a single clunk when the engine comes onto load and off again.

What would it be if it didn't do it in neutral?

[Wheeliemonsta]

Gidday ElCoyote,
It may well be a storm in a tea cup - but it definately begs some further investigation...

The 750's do have quite a significant band of vibration from about 4.5k rpm up which should clear out around 7 ~ 7.5k rpm

Might be time to get familiar with the old girl - drop the lower fairings & tank off (not difficult - just time consuming !!!) & give it a good once over...

Things I'd be checking the torque sttings on would be all the engine mounts (6 in total from memory) also check the chain for a tight spot & the nut on the output shaft sporocket (the front one !!!)
Also check both front & rear tyres are seated on the rims properly - theres generally a "Bead Seat" ring just above the bead on the tyre which goes round the circumference of the tyre.... last thing I'd check would be that you don't have an out of round tyre (I've had two rears "seperate" in the last five or so years - they look normal on the rim, it's only gyroscopic effect that allows the problem to be seen... Spinning them up on a balancer works well...)

Let's know what you find...

Cheers

[CookMySock]

perhaps the chain hasn't worn to match the sprockets yet. Try loosening the chain just ever-so-slightly and see if it changes or moves the vibration to a different RPM.

DB

[ElCoyote]

Gidday ElCoyote,
It may well be a storm in a tea cup - but it definately begs some further investigation...

The 750's do have quite a significant band of vibration from about 4.5k rpm up which should clear out around 7 ~ 7.5k rpm

Might be time to get familiar with the old girl - drop the lower fairings & tank off (not difficult - just time consuming !!!) & give it a good once over...

Things I'd be checking the torque sttings on would be all the engine mounts (6 in total from memory) also check the chain for a tight spot & the nut on the output shaft sporocket (the front one !!!)
Also check both front & rear tyres are seated on the rims properly - theres generally a "Bead Seat" ring just above the bead on the tyre which goes round the circumference of the tyre.... last thing I'd check would be that you don't have an out of round tyre (I've had two rears "seperate" in the last five or so years - they look normal on the rim, it's only gyroscopic effect that allows the problem to be seen... Spinning them up on a balancer works well...)

Let's know what you find...

Cheers

Thanks guys,
Since I first wrote this I have new chain, new tyres and checked all mounts. No obvious probs. I also checked exhaust wasn't touching frame. It seems you may be correct and it is an inherent problem as it does smooth out as you say. Guess I'll just have to ride on the redline everywhere. Ha ha ha.

[homer]

sure it no tthe cell phone in ya pocket ...... just a thought