Terrible vibration

[Just_Gasit]

Hi Scotchmo -

ISome ideas:
Epoxy a solid steel or lead rod to inside the tubes, very near the engine mounts.
Epoxy steel or lead shot inside the tubes, very near the engine mounts.
Bolt external lead mass to the outside of the tubes, not sure of best location.

The external mass (assuming lead) can be melted down at home and poured into a mold like a muffin tin to let cool. It is easy to machine and still relatively rigid for bolting.

I am thinking about bolting one or more lead masses to the tubes, using rubber or dense foam insulation between the tube and the mass. And hope frame vibrations are absorbed by the masses and compressible insulation.

Any thought about this approach?

Thanks,
MikeJ

I think your onto something here, I remember the "Bar Snake" some guys put inside the handle bar tube on their motorcross dirt bikes and heard the cheap way was to use a caulk gun and a construction sized tube of silicone sealant squeezed into the bars. How about doing this to say, the "down tube" of the bike frame? If it doesn't work, you will add a pound or so to your bike. If the tube is open at the crank and head bearing, then it could easily be squirted in.

 

[Scotchmo]

MikeJ -
Your idea to add mass to the engine will reduce the amplitude of the vibration. The mass should be as closely and rigidly connected to the engine as possible. You suggested the frame tubes. That should work if you have stiff/rigid motor mounts. If you have rubber mounts, I guess you could put the weights on the engine itself.

Here is a simplified explanation of how it will reduce the amplitude of the transmitted vibration: Imagine a one pound reciprocating mass stroking up and down one inch inside a one pound engine case. For every action, there is an opposite and equal reaction. When the one pound mass moves up or down, the center of mass of the entire engine changes so the engine tries to move up or down 0.5 inch. If you increase the mass of the engine case to ten pounds, then the amplitude of the external vibration is reduced to about 0.09 inches.

Besides reciprocating mass, there may be some rotational imbalance in the engine. It also gets a corresponding reduction in amplitude.

I don't like the idea of adding too much extra weight to reduce vibration, so I suggested tying it as rigidity as possible to the mass of the frame that is already there.

It would be nice to see if these engines are properly balanced. You cannot completely balance a single cylinder engine. You may be able to get a decent compromise on rotational balance but there will always be a reciprocating imbalance. The heavier the piston and rod, and the longer the stroke, the worse it is. That is why the 66cc engine is worse than the 49cc engine.

 

[RMWdave]

theres all kinds of things you ideally should do to make one of these perfect but thats kind of why i ride mine i guess. something to work on.

if you want to cut down vibration, send me a postage paid envelope and ill fill it up with blast shot for you to fill your handlebars with

 

[MikeJ]

Here are rotating devices (and more) that contribute to shaking and vibration, especially at higher speeds (ie, 20 mph and above).

Front tire - Frame shaking at high speeds if not balanced well.

Back tire - Frame shaking at high speeds if not balanced well.

Engine - High frequency vibrations due to large reciprocating parts.

Rear wheel sprocket - If the chain surface is not perfectly round, the constant front-to-back tensioning and relaxing of the chain while running will cause pulsing that must be absorbed by the frame and rider.

Rubber isolators - Some riders say this is good. If the chain tensions up and relaxes, the engine will rock forward and back, and a little sideways.

Solidly bolting engine to frame - Some riders say this is better. Does not allow engine to rock forward and back, nor sideways. Is less forgiving of an imperfectly mounted rear sprocket.

Weight of frame - Heavier (more mass) seems to dampen engine vibrations.

External weights bolted to frame - Untested at this time. Is simpler than weight inside frame tubes.

Road surface - Rough "chip and seal" surfaces contribute more than good pressed pavement.

Tire pressure - Somewhat softer tires will absorb vibrations from a rough road surface.


On a bicycle with a 26 inch rear wheel with a 44 tooth gear, at 30 MPH, both wheels are rotating at almost 390 times per minute, or 6.5 times per second, certainly not in sync. I have felt a bad out-of-balance bike tire condition just like an out-of-balance auto tire. The engine is spinning at almost 7,000 RPM (pretty high). A loose chain may be slapping around at 6.5 seconds as well, probably pretty hard. Have to find some way to prevent that (a spring-loaded tensioner, maybe?).

I am going to look at the items under my control, one at at time. My bike will still vibrate some, but hopefully it will be less.

I am interested in hearing if any of these points contribute to other riders. And what other riders have to contribute.

Thanks,
MikeJ

 

[cabinfever1977]

i have almost 0 vibrations even at 30mph,what stopped my vibrations was i put rubber from some old rubber handle bar grips under my engine mounts and tighten the engine mounts tight. i also switch my stock peddals for rubber peddals from a exercise bike. plus iam using cruiser tires.

 

[RMWdave]

hmm. rubber pedals thats a good idea

 

[MikeJ]

Cruiser tires is a good idea. My mountain bike knobby tires undoubtedly contribute to vibration as a reader named molotov pointed out. I should have gone cruiser tires as well when it was time to remove the previous set, but I did not know any better at the time.

 

[worldsfastestindian]

one thing that works well is using thick leather between the mounts and the frame. I havent had any vibrations, but i am also still in the break-in period.

 

[Just_Gasit]

Rubber mounts

I tried shiming the motor mount with a layer of auto heater hose opened up and wrapped around the frame, mounted nice and tight, looked real good but it didn't help. The guys that say no rubber aren't wrong. I think some of my problem is my frame is large, I'm 6 foot and I have a bike that fits me, unfortunately, this makes for long frame tubes and must be helping the resonation thoughout the bike. I'm going back to solid mounts and I have some more ideas, I'll post if they help.

 

[cabinfever1977]

i dont use auto heater hose,i use rubber handle bar grips which is softer and gets rid of all my vibrations.