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1Back to top Go down    Engine vibration on Thu Jul 26, 2018 2:27 pm

Marty

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Hi, I am experiencing unbearable engine vibrations/buzzing on my 1992 K100 RS 16v. bounceBike is converted to "cafe racer"so most of the fairing is gone. I have swapped original handle bars with the clip on's. I know I should expect more vibrations due to modifications I have made but its just impossible to ride it comfortably. I am using stock handlebar end weights and "grip puppies" yet makes no difference. Vibrations go across the bike so its not only handle bars. I can feel it on the seat, tank and foot pegs.. Its worst at around 4000RPM to 6000RPM.

Anyone have any ideas whats wrong?
Anyone in Ireland willing to have a look at the bike?

Thanks!

    

2Back to top Go down    Re: Engine vibration on Thu Jul 26, 2018 2:47 pm

Laitch

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If the driveshaft were disassembled then reassembled with the u-joints out of phase, that would be a source of vibration.

    

3Back to top Go down    Re: Engine vibration on Thu Jul 26, 2018 2:56 pm

Marty

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@Laitch wrote:If the driveshaft were disassembled then reassembled with the u-joints out of phase, that would be a source of vibration.
Thanks! Hopefully I will find an expert locally so it could be looked at.

    

4Back to top Go down    Re: Engine vibration on Thu Jul 26, 2018 5:35 pm

Two Wheels Better

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Start with some basics. How do the rubber intake boots look? And you can't always trust yer eyeballs. If they're cracked and perishing you could have vacuum leaks causing imbalance. Spray some solvent (carbie cleaner, etc) near the injectors and listen for a change in tickover rpm. Are the tyres properly balanced? These engines do have a high frequency vibe, but when all things are harmonious, they are smooth enough to not lose fillings.
An out of phase driveshaft, as suggested, is a chance, if you have no history of the bike.

    

5Back to top Go down    Re: Engine vibration on Thu Jul 26, 2018 5:48 pm

Marty

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@Two Wheels Better wrote:Start with some basics. How do the rubber intake boots look? And you can't always trust yer eyeballs. If they're cracked and perishing you could have vacuum leaks causing imbalance. Spray some solvent (carbie cleaner, etc) near the injectors and listen for a change in tickover rpm. Are the tyres properly balanced? These engines do have a high frequency vibe, but when all things are harmonious, they are smooth enough to not lose fillings.
An out of phase driveshaft, as suggested, is a chance, if you have no history of the bike.
Hi, I read a lot about rubber boots and how to test them just never did myself as they look good. I guess you right i may not see it so i will try it. Tyres are fine. Im 99% sure its coming from the engine or drive shaft.

Would mixture play part in this? i have adjustment screw but never used it and not even sure how too. I know that I'm running a bit lean by looking at my plugs.
I also read something about degree of timing to be changed to 30deg.... no idea how or even who does that.

Thanks for advise.

    

6Back to top Go down    Re: Engine vibration on Thu Jul 26, 2018 6:33 pm

Laitch

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This might be the time to describe the history of this bike, Marty.

How long have you owned it? Had you ever ridden it before it was tricked out to a cafe racer? If so, how many miles did you ride it? How did it handle? Exactly what was done to the bike to convert it? How much of the work did you do yourself? Can you list what was done? Do you know if it has ever been comprehensively tuned up and when that might have occurred?

    

7Back to top Go down    Re: Engine vibration on Fri Jul 27, 2018 7:50 am

Marty

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@Laitch wrote:This might be the time to describe the history of this bike, Marty.

How long have you owned it? Had you ever ridden it before it was tricked out to a cafe racer? If so, how many miles did you ride it? How did it handle? Exactly what was done to the bike to convert it? How much of the work did you do yourself? Can you list what was done? Do you know if it has ever been comprehensively tuned up and when that might have occurred?
Hi,

I got bike in Jan this year, fully original from Holland. bike had 120000km on the clock. I'm new to Ks and also its my first bike after 20 year gap.

I have ridden it as stock for about 3 months. No issue with vibrations at that point or I was too exited to notice it. I did not do any big trips, just a run around the mountains. I have done around 1500km since.

Conversion:
All fairing off but belly cover and under seat covers removed.
New aftermarket headlight fitted on the forks.
Front lowered by 5cm (2") in order to put clip-on handlebars.
Rear of the frame (loop) was cut off just behind the shock. Nothing welded on.
Original seat converted to a mono seat. Sits and locks in its original place.


No modifications done to the engine, suspension or drive shaft. I have no service history but bike feels original with no tune up.

Service done. (at around same time of conversion)
Engine oil 10w50 semi synthetic.
Gearbox and final drive 80w90 hypoid
Aftermarket air filter.
FUEL FILTER NOT CHANGED YET AND NOT SURE WHEN IT WAS.
All done by me.
Recently installed DR7EIX iridium spark plugs. Made no difference.
Previously used DR7EA

Just to add. when engine hot i do hear a rattle in the front of the engine when decelerating/ off the throttle. Chain?

Vibrations are very fine high pitch, almost like holing a power tool (sander for example) in my hands.



Last edited by Marty on Fri Jul 27, 2018 11:09 am; edited 1 time in total

    

8Back to top Go down    Re: Engine vibration on Fri Jul 27, 2018 8:06 am

92KK 84WW Olaf

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Marty

You mention cutting the frame and not welding anything on.

That loop at the end helps dampen vibrations within the frame.

    

9Back to top Go down    Re: Engine vibration on Fri Jul 27, 2018 10:45 am

Marty

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@92KK 84WW Olaf wrote:Marty

You mention cutting the frame and not welding anything on.

That loop at the end helps dampen vibrations within the frame.
Hi,

possibly yes, but a lot of bikes are transformed this way but I haven't heard anyone complaining about vibrations. I am following FB K bikes modified and have not heard anyone having this issue. I even asked the same question but answers were very basic...handle bar end weights, grip puppies etc.

Thanks!

    

10Back to top Go down    Re: Engine vibration on Fri Jul 27, 2018 11:48 am

92KK 84WW Olaf

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All the ones I have seen modified had a new loopwelded in but much further forward. I have never seen one without it.

    

11Back to top Go down    Re: Engine vibration on Fri Jul 27, 2018 1:11 pm

Two Wheels Better

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My Big Block's rear rails end a foot past the side to side brace of the upper shock absorber mount. It has minimal vibes, even being a 1200.

I think our subject may have TB balance issues due to vacuum leaks and/or incorrectly set throttle linkage. Need to get started on sorting that out.

Keep in mind you won't change dramatically how the bike feels in its mid and upper rpm range by turning the four brass air screws. These are more for idle balance, but if someone has mucked with the TB linkage in an effort to 'sync' the TBs, and your intake boots aren't sealed down to the cylinder head, or are cracked, vibes will happen, especially at the speed/rpm you mention it occurring at. If you lack the skill get someone to help you at least check idle balance, and while there, see what balance is at revs. There are several throttle body threads on the forum.

Also check the torque spec for all engine and gearbox to frame points.

    

12Back to top Go down    Re: Engine vibration on Fri Jul 27, 2018 3:47 pm

Marty

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@Two Wheels Better wrote:My Big Block's rear rails end a foot past the side to side brace of the upper shock absorber mount. It has minimal vibes, even being a 1200.

I think our subject may have TB balance issues due to vacuum leaks and/or incorrectly set throttle linkage. Need to get started on sorting that out.

Keep in mind you won't change dramatically how the bike feels in its mid and upper rpm range by turning the four brass air screws. These are more for idle balance, but if someone has mucked with the TB linkage in an effort to 'sync' the TBs, and your intake boots aren't sealed down to the cylinder head, or are cracked, vibes will happen, especially at the speed/rpm you mention it occurring at. If you lack the skill get someone to help you at least check idle balance, and while there, see what balance is at revs. There are several throttle body threads on the forum.

Also check the torque spec for all engine and gearbox to frame points.
All my throttle adjustment screws still have original setting with blue untouched paint on them. I will see if I have any leaks first.

Thanks!

    

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