siamoto supermoto 125 vibration help please

[billy5641]

please can anyone help
my 17 year old son has just bought a siamoto 125 supermoto
to be fair it looks ok and runs like a sawing machine ........that is untill you rev it to over 4k revs it vibrates better than a rampant rabbit!
can anyone tell me if this is what they are all like or is there somthing wrong with it ? it does get less over 8k revs
any help appreciated

[lllN30lll]

is that one of the 4 stroke chinese replicas?


normally they are put together quite badly, take your time and go round the bike, check EVERY single nut/bolt to make sure they're tight.

the only thing that rattles on my brothers now is the Bash plate at the bottom of the frame
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Turbo R1
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[billy5641]

hi yes its the 4 stroke,
i have stripped it down and retightened everything for him ,but it still vibrates .....exessivly .....above 4k revs
i would like to know if this is common with bikes of this type ?

[stinkwheel]

Can be a problem with single cylinder bikes (or indeed any bike, more so with singles though).

Providing the engine seems like it is running fine, it is probably just a simple problem of some of the cycle parts vibrating in sympathy with the engine.

First off, check the engine mounting bolts are all tight and that there is no damage to any of the mounting plates. After that it is a case of trying to either isolate the parts in question from the vibration or altering the frequency at which they vibrate.

Old British bikes used to have this sort of problem to the extent that you had to check all the nuts and bolts on some of them every 500 miles or so to make sure they hadn't rattled loose. A common 'fix' was to cut out bits of inner tube and fit them under the mountings for the footpegs and the handlebar clamps.

Other things to try include altering the weight of the handlebars so they vibrate at a different frequency. This can be achieved by fitting some bar-end weights or even by filling the bars with sand, lead shot or expanding foam in extreme cases. Even some recently designed bikes seem to have this problem, noteably the Kawasaki Z750.

Another tip I saw on here is to loosen the engine mounting bolts then put a car jack under the engine, jack it up slightly and tighten the bolts again. There is always a small amount of play in any frame/engine coupling (even if you can't see it), if the tolerances were too fine the engine wouldn't fit in the frame due to slight manufacturing variations. Effectively, you would be slightly altering the position of the engine in the frame which should alter the frequency at which it vibrates.

[billy5641]

thanks mr wheel
tightened engine mounts and found one is broken!
welded it up and its as smooth running as i gues it ever will be
cheers

[Finglonga]

[billy5641]

no its not new .................do they still sell these ??????????

[lilredmachine]

To be quite honest the weld is probably much stronger than the original bracket, so don't expect it to fall apart.
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