Vibrations: not necessarily good

Had occasion to head off to the northwest this weekend, which involved a 250k each way trip.

The bike was grand apart from some fairly concerning vibration.

It is engine vibes and felt primarily through the pegs from about 4.5, 5k and upward.

It is definitely engine as opposed to running gear as it rolls smoothly with the clutch in, even at 120kph.

On a straight run taking it up to a fair lick, say 7k rpm in fifth, it got uncomfortable to hold onto as it was fairly noticeable through the bars by then too.

I had an old ST4s (996 Desmoquatro) that wore through a main journal shell and it kind of felt like the early stages of that, but more pronounced as the revs rose.

It is not a thumpy, knocky sort of vibe, but a fairty high frequency one that gets worse as the revs rise.

It doesn’t really feel like the grindy sort of vibe from a fecked bearing, it is a bit more buzzy than that.

Anyone have similar experience?

A

Came across similar symptoms once before,the solution was to Retorque all the engine mounting bolts to original settings
Regards Bif

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Must be worn out after doing 500,000 Ks

Yeah, but, no, but… I didn’t say 250,000 of what, did I?
Could have been leptons, could have been 'thou…

Still vibrates, though.

I agree with bif. Time to re-torque your chassis to eliminate that possibility. Friend ran into the exact issue not long ago.

Yeah, could well be. Also noticed that the right hand silencer bracket had cracked thought half the mount. Could well be a contributing factor.

Did a bit of investigating last night and all of the engine mounts seem to be torqued up nicely.

I had moved to a one tooth smaller front sprocket recently, and I thought that might have something to do with it. There is a small bit of play on the shaft, as one would expect, but nothing that would cause the kind of vibes I’m getting. Also the chain run is dead straight and the tension is on the loose side of spec.

The vibes seem to be most noticeable through the pegs and seat, though they come through the bars too. From about 4,500rpm they become noticeable. It was always a bit rough through this range, but it had been suggested before that worn carb needles would mean that as it goes from slow to main jets, the fuelling could be causing a bit of vibration, but again, this doesn’t seem to add up.

I’m a bit concerned now, as they are more intrusive than they used to be.

Has anyone had experience of big ends going? How did it manifest?

Cheers,
A

Hi Ascalon, I had a big end bearing go, my symptoms were a initially a insignificant knock at tick over and what appeared to be a slightly rough patch at low revs which you could blend out with the throttle, I initially cleaned the carbs thinking a slow jet was blocked, took the bike out for a test run down the bypass, first run the bike felt like it was holding back at about 8k revs, second run it destroyed its self :worried::joy:

Thanks for that Pete.

I decided to do a little more exploratory work today and dropped the oil.

The oil was dark, but not mucky, so that was good. Nothing on the sump plug either.

I went through the drained oil with a pick-up magnet and nothing came back, the same with a magnet into the filter. So I’m confident it is nothing eating itself inside the engine.

I did the screwdriver stethoscope trick and all four heads and barrels sound the same, which is also good. Each down pipe seems to be heating up evenly, so I don;t think it is spark or plugs either.

The only thing I can think of now is really badly out of sync carbs. Yesterday I opened the airbox and everything as far as the carbs was fine too, bad the odd wasp int he K&N filter.

I know carbs tend to show out of sync lower in the range, but I’ve also heard V-fours are more susceptible than inline 4s.

Thoughts?

A

Due to the kind hearted nature of a local forumite, I borrowed a set of manometers to balance the carbs.

As you can see, they were a little out!

But with a bit of fiddling, things started coming within range

Back a bit, down a bit, nearly there…

Feck it, that’ll do!

So, did it do anything about the engine vibes?

As we would say colloquially:

“It did in me hole!”

Still, one more thing eliminated.

The search goes on.

UPDATE: Having talked over the issue with my brother, an engineer and long time bike fettler, his suggestion was a cracked engine mount or bolt.

Which makes sense. Damn.

The frame is powder coated, so it might not even show up directly.

Will investigate.

Anyone any experience of such? Any particular weak points?

“I had moved to a one tooth smaller front sprocket recently” ???
Its a strong motor, hardly works for a living at 100kph.
Put it in neutral, rev it up to 4500rpm,… it’ll Buzz Lots.
I did a tour once with more teeth on the rear sprocket, Big Mistake,…
Buzz’d a lot, used up gas (and motor).
Then I went the other way, moving from 17 to 18T Primary.
Engine got much quieter, buzz went away, RPMs drop’d to 4000 @ 100kph.
It makes putting around in 1st a little harder, but I get 450km on a tank (carbs set right too).

ReTorquing does not mean Checking Torque.
UnTorque ALL bolts at Once, then Torque all back up (preferably All at Once (each a little at a time)).

Those Carb Syncs are still Out, should All be Equal. If you can’t get it, there is a problem somewhere.
Some of those adjustments are Compound, (one adjustment effects 2 carbs at once).
It takes some thinking & fiddling.

Check Exhaust System mounting bolts.

Thanks for the response.
Yes, I know the carbs are still out, but they are a lot closer than they used to be, but the exercise served its purpose insofar as it showed that the carbs sync was not a contributory factor to the vibes.

Also, vibes weren’t there before. Even with the previous sprocket and seriously knackered chain, at the same revs, the vibes were not that bad. This is a new development.

Agreed on the engine mount torques though, I think it would be best to actually undo them all and torque them from hand tight back up to full.

Have checked the exhaust mounts, all seem to be OK.

I am reading this and hoping that you come up with the problem because it sounds exactly like the same problem I am having with mine. I am hoping it is something minor but the way my luck has been lately I aint holding my breath!
Good luck!

Is the detachable frame rail tight ?

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@vf_pete: Yeah, tried that too. All tight.

Update:
Last night, with the manual in hand for all the correct torque settings, I loosened all the engine mount bolts with the bike on the centre stand.

I loosened each one very carefully to the point there was no play, but no tension either.
I then followed the old procedure of opposites and diagonals to re-torque each mount.

That all went fine,except the lower left front mount bolt feels like it is not tightening properly. I suspect a stripped thread.
However, on the ride to work this morning there is a significant reduction in the intrusive vibes, particularly in the upper ranges. So now, the 120kph plus range is vastly smoother than it was and holding the cruise speed is no longer like hugging a sander.

It has not eliminated the vibes by any means, but it has significantly changed the character of them, reduving them in places, which leads me to believe this is the root cause.

The fact that a front engine mount (the14mm bolt) is not properly tightening up too can only by a contributory factor.

I’ll get a helicoil kit for the bolt and sort it out.

We’ll see how it develops.

Right, silly me!

The engine mount I was worried about at the front has a nut on it, not a direct mount!

This is good news and bad news. Bad news because it means I’m a numpty, but good in that I don’t need a helicoil.

So, I went through the motions again, but based on the experience last time, I loosened all mounts, but this time, I started at the back and went in order of magnitude.
I torqued from biggest to smallest and then did the two large ones at the front. Then I did up the smaller ones, back and front.
This seems to have made the most difference, as before, it has changed the character of the vibes and reduced them a bit more. It is still vibey between 4 and 5,500 rpm, but cruising at 120 kph + in top is now a much more civil affair and the vibes in the middle are most noticeable rev’ing through than when having to hold it.

To be honest, I’m happy enough with that.

A