Surging vibes through bike at 70mph+

[sopwith camel]

Just returned from from 3000 mile round trip to Morocco. Cracking trip and the bike (1150GSA) ran well, but have picked up a couple of problems as a result:

1) Between 75-80 mph, after holding a steady speed for half a minute or so, I get a rhythmic surging vibration coming through the bars and pegs, 1-2 times a second. Thought it could be wheel bearings?? No oil leaking from final drive, so not so sure it's the final drive bearing.

2) Also noticed that when I shut the throttle down quickly at anything over 30 mph, the bike 'dips' sharply down to the right - feels like the pull is coming from the right cylinder head?

Not sure if two are linked?? Gonna start doing some investigation in the coming days, but thought I'd see if anyone could shed some light on where the best place to start looking might be..??

 

[Timolgra]

I'd try setting the valve clearance + rocker end float and then balancing the throttles before worrying too much

 

[Wingit]

Are you on knobblies? And what state are they in after the trip? I get a rhythmic vibe out of mine at certain speeds (although it's a much lighter bike).

 

[buellzebub]

I don't know about the vibes but I'd guess the dipping is due to torque reaction from the flywheel (or is it inertia? It's been a long time since my physics lessons ). It's the opposite of when you blip the throttle at a standstill and the bike kicks to the side a little (well mine does anyway!)

 

[stolzy]

I don't know about the vibes but I'd guess the dipping is due to torque reaction from the flywheel (or is it inertia? It's been a long time since my physics lessons ). It's the opposite of when you blip the throttle at a standstill and the bike kicks to the side a little (well mine does anyway!)

That's what I thought, but the torque reaction surely works the other way - if you blip the throttle it pulls the bike to the right - presumably if you roll off suddenly it would pull to the left - the opposite of what the OP sees.

 

[DrFarkoff]

Surging Vibration? Tyre Balance, tyre wear, propshaft UJ on way out,

I never did find what it was on mine Mechanically it was a near as damn it to spec It still had a vibration I suspect the last person to do the clutch before me to have misaligned the clutch components

But they wiped off any trace of balance marks So I lived with it

 

[buellzebub]

That's what I thought, but the torque reaction surely works the other way - if you blip the throttle it pulls the bike to the right - presumably if you roll off suddenly it would pull to the left - the opposite of what the OP sees.

Yes, thinking about it, you're absolutely right.

 

[stolzy]

Yes, thinking about it, you're absolutely right.

That's not something I hear every day
Doubtless Steptoe will be along in a minute to tell me I'm wrong

 

[sopwith camel]

Cheers all.

Had the first post-tour wash and initial check...

Rear wheel won't spin freely out of gear, and has 1cm+ lateral play. Ran the bike in first gear on stand to listen to drive, and didn't sound pretty. Hoping it's nothing more than wheel bearings, and not a problem with the diff

Gonna look for a thread re: checking wheel bearings. Already found the final drive bearing post, but would've thought that wouldn't explain the lateral play in the wheel??

Also managed to trash my Remus can - completely split the whole way round. If that wasn't annoying enough, it decided to melt a hole through my pannier. Me thinks a set of metal tins on the back might be in order in due course. BMW probably knew what they were doing when they added the original stainless steel can. Lucky I kept the original and collector box...

Any further tips re the above appreciated btw...