Bizarre vibration. Not good.

[Guest Peterpoddy]

I do a lot of miles on my 700X. Coming up to 34k now, 1000 miles a month, so I know it very very well. 

On the ride into work today I suddenly became aware of a new vibration at my usual 55/45mph (average speed camera stretch) at 2800rpm cruising speed

Clutch in and revs off and it goes away so it's not wheels, drivetrain or suspension, clutch in and hold 2800 rpm and it's still there, so I doubt it's gearbox, and it gets a bit worse if I stay in gear and back off the throttle. 

Its not a misfire, it just feels like something in the engine is out of balance or not right. 

Could the valve clearances have changed that quickly? Spark plug or HT lead?

Any other ideas?

I can't see anything obviously wrong and I've got 26 miles on the way home to think about it.....

[Guest Mac750]

Engine mounting bolts loose ?

[Guest Peterpoddy]

I'm back home now

 

Yes engine mountings did occour to me as well. I'll check those. 

It was still there as I pulled out of work in the 20-30 mph traffic near us, and it's a brand new road surface so very noticeable. 

It did seem to die back as speed crept up so I experimented I noted it's mainly between 2500-3200 rpm (where I spend a lot of time) at light throttle or on overrun. Give it more gas and the bigger vibes of the engine swamp it. 

It didn't seem as bad though. At 55mph I can't really notice it and at 70-75 everything is totally normal. It's the slow speed/light throttle where it's noticeable. 

 

I'll keep tabs on it and see how it goes. I was going to do the next service myself so I'll change the plugs whilst I'm at it, but it's not due another service for 1000 miles or so. We shall see.....

[Tex 36,817]

Very mysterious! Keep us posted matey.

[trisaki 2,029]

Too high and gear too few revs ! my 700x  feels rough if I'm in say 4th  when really I should be in 2nd  or 3rd  

[Guest technophebe]

I recently had an annual service, and the mechanic noted that one of the big bolts on the side of the bike that hold various stuff on was almost loose enough to fall out. It was the one that your right leg rubs on when your foot's on the peg.

 

I'd noticed a bit of extra vibration recently but thought it was just my imagination. Worth a thought anyway?

Edited November 5, 2016 by technophebe

[Guest Mac750]

Had the engine bolts loosen on a TDM, it felt much as you described worth a look.  Also check chain tension and condition of rear sprocket, rear wheel alignment and tyre condition. All worth checking. 

[Guest Peterpoddy]

So anyway, it sort of came and went for a bit, some days better, some worse, but never getting too bad. I came to the conclusion that I was being overly picky.

A couple of days ago I serviced the bike and replaced the plugs, and it's now noticeably smoother.

i've had this before on a car, if you don't change the plugs that often you really notice when you do get round to it..! I'll be changing them every 24k miles now, not every 32k as in the service schedule

[Tex 36,817]

Thanks for the update, Peter. One to bear in mind for future reference.