Vibration developed at 4000revs today

[hughguzzi]

Just found Stepoes thread with a great pictorial of how to set up rocker end float and tappets - I'll give that a try .....
www.ukgser.com/forums/showthread.php?t=81408
Thanks for the suggestion Johnwhit - Sherlocks just set up the throttle bodies which made tickover and running at steady lower revs better but didnt help the 4000revs vib at all ....

 

[Johnwhit]

I'm just wondering if they set the 'ballance' for low revs & didnt set the high rev part of the engine correct or look at it at all. I would expect that if the valves or end float (or anything else) was out enough to cause the engine to vibrate it would show when setting the cyl sync up and then they wouldnt be able to ballance them.
A smooth engine needs to have both pistons pulling the same and for your mechanic to say the problem isnt bad when he tested it would make me worry IMHO
Even a plug breaking down or valves not sealing properly would show on the guage,(unless you have a problem that is related to both heads , but I wouldnt think that) the GS engine is basically two motors in one and I would guess that unless its fuel preasure or an electrical prob thats affecting both sides it should show up when syncing the engine.
just a thought,
John

 

[kwallace21]

vibes at 4k

My 1150 GSA Twinspark does exactly the same. It is however intermittant.
One day it will be super smooth, (well as smooth as one of these big lumps can be), the next day it will develop some increased vibes from 3800rpm to about 4500rpm where it then goes away. It happens in any gear at any speed but always starts at 3800rpm so it must be engine related. Cant see how it can be gearbox or clutch related as it only happens at an exact rev range and not at a specific speed or gear. It isn't unrideable when it happens, just more vibey than usual.
Changed the stick coils once and it didn't make any diffference. Valves, tb's and end float all ok. Why the hell is it intermittent. It can even go from smooth to vibey on the same day if you stop and switch off the engine then start again.
It's a bloody mystery!
Steptoe, Help!

cheers
Kev

 

[warmshed]

That's the same speed the input shaft of the gearbox will be turning. A flaky bearing on the input shaft would give the same symptoms.

 

[hughguzzi]

Just a thought, but if when riding I got the revs to 4000 (point of vibration) and pulled in the clutch - keeping the revs, that would reduce the revs of the clutch + gearbox input shaft (which comes from the clutch?) as the bike decelerates ?
Could I assume that if the vibration went then the problem is indeed the clutch/input shaft, but if the vibs remain then it should be the engine itself ?
Could this be done on main stand ? (obviously bike in gear as if riding)
Surely that would at least reduce the possibilities ?

So far kind suggestions which I think possible for engine revs (not speed) related vibs have been -

worn clutch & bit has come off friction plate leading to imbalance
Input shaft bearing
coils
rocker end float
throttle body balance
loose items

 

[warmshed]

Just a thought, but if when riding I got the revs to 4000 (point of vibration) and pulled in the clutch - keeping the revs, that would reduce the revs of the clutch + gearbox input shaft (which comes from the clutch?) as the bike decelerates ?
Could I assume that if the vibration went then the problem is indeed the clutch/input shaft, but if the vibs remain then it should be the engine itself ?
Could this be done on main stand ? (obviously bike in gear as if riding)
Surely that would at least reduce the possibilities ?

So far kind suggestions which I think possible for engine revs (not speed) related vibs have been -

worn clutch & bit has come off friction plate leading to imbalance
Input shaft bearing
coils
rocker end float
throttle body balance
loose items

That's what I mentioned 10 post earlier. However once the clutch is pulled in the loading is also off the mainshaft of the gearbox so if this was at fault the vibration could still disappear, however if it is still there you could rule out the engine.

 

[CPL]

If it's just vibration, and it's not accompanied by rattling, knocking or ticking at the same frequency, I doubt that it's an engine bearing... If it were main bearings, you'd expect the vibration to stop if you pull the clutch in. Conversely, with big ends/little ends, the thing would knock, or rattle worse as the revs rise. If there is an imbalance however, the vibration itself will eventually knacker the mains....

I would NEVER run the bike in gear, on the stand, because there will be zero constant pressure on the gears, making it very likely that the load will transfer very quickly from drive, to overrun and that sort of "rattling" from one side of the dog teeth to the other might even throw up more strange vibrations. Not to mention sending the shock through bearings and driveshaft/bevel Etc.

Providing the vibration is only at one fixed rpm I would be tempted to temporarily avoid that engine speed as much as possible and see if it gets worse, or even goes away, but if it persists, I'd take it to an expert for a look at less expensive possibilities, such as fuelling etc first and if it is a gearbox bearing, take the opportunity to save yourself some money by having a new clutch fitted while the engine and box are apart... At the current mileage, you'll be needing one soon anyway if it hasn't already been done.