bad bad vibrations

[fredric3144]

My 80cc motor is now working better I'm getting better speed but once I start getting over 25 mph the bike starts vibrating so bad by teeth start chattering . I am happy with it though having great fun riding below 25 mph . The first motor I had on this bike was 50cc it vibrated also the fenders broke off . I finished taking them off and was able to get speeds up to about 35 or 40 mph . I think didn't have a speedometer then as I do now . Any ideas about how to stop this vibration or should I just be happy with 25 mph .

 

[Trey]

Can you give us some more info- what kind of bike you have, where it feels like it's coming from, that sort of stuff. Pictures would be great.

For me, 20mph is plenty! 40mph? You need to talk to scotto.

 

[fredric3144]

I took some pics but they didn't turn out very well will take some better ones in the morning my bike is a walmart $99 special mountain bike have done a little change to it I put a larger tire on the rear with bigger spokes . The vibration is from the motor itself I plan to recheck my mounting perhaps use some pieces of old tube to put between the motor and bike . I agree 20mph is fine actualy I'm in no real hurry at any time . I do like the 80cc as it climbs up hills without help or at least all I have tried it on so far . Heck I'm 66 and to darn lazy to do a whole lot of peddling lol

 

[Nashville Kat]

Smaller motor sprocket- try a 36 or smaller- the fewer the revs, the less the vibrations and better cruising speed- dif between a kit 44 and 36 is tremendous.

also smooth tires- knobbys will always get vibration at good speeds-

rubber in motor mounts helps too

shock seat post
shock fork

 

[Desert Rat]

If you want vibrations rubber in the mounts is the way to go
google it here, these motors were made to be solidly mounted
I've heard more horror stories than I care to about rubber in the mounts!

http://www.google.com/cse?cx=partne...c.tab=0&gsc.q=mounting with rubber&gsc.page=1

I personally have learned this over a few builds

 

[2door]

DO NOT USE RUBBER IN YOUR MOUNTS!!!!! Bad advice and will only lead to failure of fasteners or worse. As said above, these engines are designed to be mounted solid to the frame. And as tightly as possible.

"Bad vibration" is a relative term. How bad is "bad"? All single cylinder 2 stroke engines will vibrate. Its the nature of the beast but new builders will often not expect how much vibration can be produced and think something is wrong. It might well be that what you're feeling is normal. You'll hear "my engine runs smooth", again, "smooth" is arbitrary.
What is "smooth" by some people's standards might be "vibrates bad" by another.

As for fenders/brackets falling off; there is a lot of good information here regarding fenders because vibration damage to fender brackets and braces is a normal result of motorizing a bike.

Tom

 

[crassius]

we had some RICO motors last year that shook badly - no way to get around it & most hammered the mains flat pretty quickly

seemed to be old, unbalanced 50cc cranks with 66cc top ends fitted to them - just hoping to never see another of those : (

 

[fatdaddy]

Hey Fred, PLEASE listen to 2door. NO RUBBER.
A big reason you may get vibration is the motor mounts not being tight enough. NOW, getting the mounts tight enough is hard to do with the stock studs and nuts. They will strip out before you can get them that tight. The chinese don't care if you strip out a stud, They will claim you OVER tightened it.
While riding a few weeks ago I started getting A LOT of vibration. I thought my engine was going bad. I got home with it, Checked it out and all it was...A loose front mount.
So replace the studs and nuts, ALL of them, with better quality, then tighten them up. Ya still gotta be carefull because the studs screw into a cheap chinese motor case. But you can still get them tighter. I think you'll find the vibes are greatly reduced or even eliminated.
AND NO RUBBER.
fatdaddy.

 

[fredric3144]

Went out today and totally remounted my motor no rubber .no bad vibration untill i hit full throdle I have no idea how fast that is . I have but 2 speedometers on my bike so far . The first was a cheap ebay electronic that kept good time but did nothing else . The second one was a old school type that worked for about 10 miles and now gives a swinging needle that tells nothing . I'll try another one after the 3rd of when i get my social security check .

 

[bairdco]

rubber is definitely bad for motor mounts. you won't find one experienced builder who uses it.

the two biggest vibration causing things everyone overlooks is the gas tank and the exhaust.

and the gas tank is one place where rubber mounting actually helps!

the easiest thing to do is cut up an old innertube and wrap it around the top tube on the frame, then mount your tank on top of it. tighten it up so it doesn't move, but not so tight that the studs break and crack your tank.

the hanging exhaust pipe will also cause vibes, and without mounting it to the frame, either with the crappy strap the kit comes with, or some plumber's pipe strap, or whatever you can come up with, it'll vibrate, come loose, and break or strip the studs in the engine.

a simple test which i've mentioned many, many times, is lean your knee into the tank when the vibes start. you should feel them decrease or go away.

you can also put your foot against the exhaust pipe for the same type of test, if you don't mind losing a little shoe rubber...

any loose parts will cause vibrations. some minor, some serious.

and if your bike ever suddenly starts vibrating when it never did before, something's usually broken. like your frame. happened to me...

 

[fredric3144]

I have since changed my mounting of motor . My rear mount is the same . My front mount I took a 10 inch pipe put that in the motor mount , then when mounted to bike I used screw type hose clamps on each end of the pipe to hold it on bike . Makes a solid mount and almost all of the real bad vibrations are gone .

 

[aa_ron]

Sometimes rubber makes the vibrations worse i use rubber between the motor and the frame ont the back mount and leave the front mount metal on metal and have had great luck so far. I have built 4 this way and none have vibrated to any sort of extreme yet.

 

[2door]

Sometimes rubber makes the vibrations worse i use rubber between the motor and the frame ont the back mount and leave the front mount metal on metal and have had great luck so far. I have built 4 this way and none have vibrated to any sort of extreme yet.

It will. Give it time.
If you put enough miles on your bikes the rubber will compress and wear allowing the vibrations to be concentrated on the front mount and the fasteners.

There is the old argument that motorcycles, cars, outboard engines etc are mounted in rubber. The problem with that is the concept is entirely different. Resilient mounts in the vehicles and applications mentioned have a metal, rubber, metal sandwich. The mount fasteners are never subjected to the vibrations produced by the engine. They simply hold the resilient sandwich in place.

Rubber mounting a bicycle engine by placing rubber between the engine and the bike frame will not eliminate vibrations but transfer them directly to the mount and the fasteners.

It might work, for a while, but eventually something's going to break. Guaranteed.

Tom

 

[Jesse_James]

My exhaust pipe is really bad with falling off. Even if I tightened it good the nuts securing it will loosen and eventually it will fall off why is this? What can be done?

 

[maniac57]

My exhaust pipe is really bad with falling off. Even if I tightened it good the nuts securing it will loosen and eventually it will fall off why is this? What can be done?

Add a hanger to support it somewhere besides the exhaust port. The vibration causes it to whip around when unbraced and can lead to broken exhaust studs or worse.

 

[Tyler6357]

I use rubber, mostly to protect the paint on the frame, not so much for dampen vibrations. I use it under the gas tank, it keeps the tank in place without needing to tighten it too tight to the frame. This allows the tank to move slightly so if I ever wreck and my junk hits the tank it will give a bit.

 

[2door]

I use rubber, mostly to protect the paint on the frame, not so much for dampen vibrations. I use it under the gas tank, it keeps the tank in place without needing to tighten it too tight to the frame. This allows the tank to move slightly so if I ever wreck and my junk hits the tank it will give a bit.

Rubber under the fuel tank is fine. The tank isn't producing vibration but is susceptible to them. Isolating the tank with a resilient material is actually a good idea. Not so for engine mounts for the reasons that have been discussed here many times. Even a thin layer of rubber, old inner tube, etc, in the engine mounts will eventually allow the mounts to loosen with predictable results.

Tom

 

[bairdco]

to expand on tom's post, although the tank doesn't produce vibes, it definitely enhances them. the tank can resonate with the motor and cause your whole bike to shake. put a half full can of beer on a speaker and turn up the bass and you'll see what i mean.

wrapping an old innertube or something around the top tube of the frame under the tank and it'll stop it.

 

[Jesse_James]

Add a hanger to support it somewhere besides the exhaust port. The vibration causes it to whip around when unbraced and can lead to broken exhaust studs or worse.

are the studs are the threaded rods? Can I just take those threaded rods out and instead use bolts?

 

[Mr. Minecraft]

I just wanted to say as an interesting fact that Phantom Bikes builds all of their bikes, even the $3k ones, with rubber in the mounts. I still agree that rubber is bad, just thought this might be interesting.