The vibrations are KILLING me

GoldenMotor.com

Basement Cat

New Member
Mar 14, 2011
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Florida
Hey guys,

I just finished my first MB build using a 60cc China HT engine. It runs just fine but I'm getting these unbearable vibrations in my hands the faster I go. It's so bad that anything above 1/2 throttle hurts my hands really badly.

I've tried putting sand in the handlebars to weigh them down and I have one of those olde stems with rubber bushings that are supposed to dampen vibrations but this isn't enough. I've tried searching the forums but I'm having difficulty finding the information that I need.

Any help would be greatly appreciated!

PS: My top speed is 30 mph with the stock sprockets on the 60cc engine, is that what I should be expecting form this engine?
 

The_Aleman

Active Member
Jul 31, 2008
2,653
4
38
el People's Republik de Kalifornistan
Make sure the mounts are sitting flat against the frame and the muffler is also clamped to the frame.
Also, you might want to get a smaller rear sprocket. That way you'll be turning less RPM at 25-30MPH.
I recommend a 36T. These engines make nice power at 4000-5000RPM. Gear yourself accordingly!
 

sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
1,839
471
83
california
From my experience excess vibration is often caused by misalignment of the chain and sprockets. Stand behind the bike and look from the rear sprocket up to the engine sprocket. Look for deflection in the chain. Also, make sure your engine is not rotated to the left or right of frame centerline.
 

Al.Fisherman

New Member
Sep 9, 2009
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Calera, Alabama
My first build was as you described. I mounted my engine as it is supposed to be mounted. Sprocket was perfect. Chain no problem. Then one day I cracked the frame and had to switch frames....no more vibration.
 

PerryP180

New Member
Jun 24, 2011
79
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Atlanta, GA
Make sure the motor mounts are snug. I wound up putting some inner-tube around the bike frame at the mounts. Surprisingly this made a significant difference. Make sure the front tire isn't flattened in a spot also.
 

Goat Herder

Gutter Rider
Apr 28, 2008
6,237
20
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N.M.
Make sure the muffler is mounted securely. Just hanging off the jug is not enough IMO . A surprising amount of vibs can come from a vibrating muffler.
 

Goat Herder

Gutter Rider
Apr 28, 2008
6,237
20
38
N.M.
What's a good way to mount the muffler besides just relying on the jug?
You could use a perfect size muffler clamp to match your bikes tubing. Custom bend some flat stock band steel
wrap around the muffler to reach the muffler clamp.

You could even tack weld part of this fastening arrangement to the muffler. Thing is all of this is a matched effort . The motor will need to be mounted solid. You could slot your holes in the muffler clamp down to muffler pipe junction set up a little.

Most all of these kits come with a little band clap for the muffler to fasten to the down tube. Granted it is a cheesy one it still can make a difference are you using it?
 

Basement Cat

New Member
Mar 14, 2011
26
0
0
Florida
Most all of these kits come with a little band clap for the muffler to fasten to the down tube. Granted it is a cheesy one it still can make a difference are you using it?
I feel like such a noob but I don't know how to use it with my frame. I'll post pictures of how I set up my engine kit tomorrow when the sun's out. I might have set something up wrong... :(

Also, I popped open the clutch side cover and the flathead bolts that goes on the little gear was completely loosened. Could this have been causing my problem?

I feel so stupid; I've been building and porting 2 strokes for 5 years and I can't even get this bicycle engine kit right, lol. I'm really hoping that I don't have to balance the crank...
 

biknut

Well-Known Member
Sep 28, 2010
6,631
409
83
Dallas
Make sure the mounts are sitting flat against the frame and the muffler is also clamped to the frame.
Also, you might want to get a smaller rear sprocket. That way you'll be turning less RPM at 25-30MPH.
I recommend a 36T. These engines make nice power at 4000-5000RPM. Gear yourself accordingly![/
QUOTE]

Aleman is offering good advise. China Girl motors aren't that bad vibration wise below about 5500 rpm. If you have 26" wheels and a stock 44T sprocket, 5500 is only going to be about 23 or 24 mph, so 30 mph would be way into the vibration zone, probably about 7000 rpm.

The easiest way to reduce vibration is to gear for higher top speed. I also recommend a 36T sprocket.

If the president of the 20 MPH Club can have one so can I haha.
 
Last edited:

The_Aleman

Active Member
Jul 31, 2008
2,653
4
38
el People's Republik de Kalifornistan
Well, the point is the chinagirls aren't exactly balanced or blueprinted lol...I've had 5 of em, and they all danced a little different.
When you spin an engine 6000RPM, the crankshaft is spinning over 100x a second! Think about that!
Any imperfections in balance will be magnified of course, so if you get an engine that's off, really, what can ya do but lower the revs?

I have kind of a built-in rev-limiter myself..I don't really like spinning my engines over that 6K mark.
None of my 2-strokes liked it either. With my 34T, they purred happily.
My 4-stroke does 30MPH at 6K RPM, and it makes maximum HP at 34 :D
 

Basement Cat

New Member
Mar 14, 2011
26
0
0
Florida
I didn't realize these engines were built to rev so low. Some of my Go-Ped engines easily rev up to 18k under load and the lowest revving engine I've built went up to 12-12.5k, lol. I suppose I'll just go slower for now :(
 

KDB

New Member
Jun 19, 2011
47
0
0
Maryland
I made motor mounts out of my old rubber handlegrips. appear to help some.

I've got a picture of my setup, does it look right?
It looks just like mine, not that that means anything. My first build too and less than two weeks on the road.

Also, the crankcase is leaking fuel/oil. Has anyone else had this issue?
Some experenced person please answer. I have this same problem and appear to be leaking more than I burn.
 

PerryP180

New Member
Jun 24, 2011
79
1
0
Atlanta, GA
You have the NT carb in the photo. I had what I thought was fuel leaking from the engine. After many hours of searching I found the leak to actually be on the nipple where the fuel line connects to the carb. The nipple is so close to the carb wall that I couldn't get the black fuel lines to seat properly. The walls of the fuel line are too thick. I've gone back to a clear fuel line (has thinner walls), used a small zip tie to clamp it and I've had no problem. I also put the sip ties on all points where the fuel line is over a nipple. (fuel filter and petcock) The clear line works but it does expand in heat and it will get brittle in a few months and need replacing. As for engine vibration, sound like the mounts aren't tight enough. Also remember that the smaller the bike frame the worse the vibration will be. I tried a small framed mountain bike and the vibration was significant. I now use larger frame cruisers and have very little.
 

Dan

Staff
May 25, 2008
12,765
115
48
58
Moosylvania
All great advise and just to add, Harbor freight has these great ridding gloves meant for jack-hammering. Well padded on the palms and finger less. Like 8 bucks or some thing. The fingerless part is great to in that you can do adjustments with out taking em off. Called "Vibrato" or some thing like that.

Also a great help is a bent or lay back seat post so your not ridding on you feet and hands. Makes a huge difference. With the engine doing the work, no need to have your weight so far forward and over the pedals. Might want cruiser handle bars with em though.
 

biknut

Well-Known Member
Sep 28, 2010
6,631
409
83
Dallas
All single cylinder motors vibrate like paint shakers at certain rpm. All you can accomplish by balancing your motor is to change the rpm where it vibrates the most. It's impossible to balance for all speeds. For cruising around on a MB the trick is to gear your bike tall enough to not be running in it's worst vibration zone when you get it up to battle speed.

China Girls aren't racers, so they're not balanced to be smooth near red line. Mine all feel smoothest closer to maximum torque.