Engine Vibration

old motorbike

New Member
Sep 21, 2008
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I searched but didn't find any info.
Is the a way to balance the (80cc?) engine (crank,rod and piston)
Does anyone know a shop that can do this? Mine vibrates so bad after about 3-4 k that I believe it looses 1/2 of it's potential performance.
 

velardejose

New Member
Sep 9, 2008
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Lima, Peru
Good idea
I will visit a friend who has a big machine shop, has a dynamic balancer machine
He has experience with all types of racing engines, must know about single cylinder balancing
Peace
 

thatsdax

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Feb 22, 2008
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For Starters, there is no such thing as an 80cc. As for vibration, I have never had vibration that was objectionable. My 2 choppers I built are border line. That is because of the low gearing. Which means this.. If you lower the size of your rear sprocket, and make sure your mounts are tight, you should be fine with vibrations. Also.. Wearing good gloves will also help. Enjoy the ride...
 

amealnet

New Member
Sep 19, 2008
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what about adding rubber under the mounts like chainsaws have to reduce vibration


i used the rubber car exhaust hangers and cut them to fit my mounting brackets, hardly feel the engine running, smooth as silk.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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up north now
Yes, pictures? If you can rubber mount and get the engine to stay still enough to keep the chain on, you are doing well. I have found that the lead absorbs the vibration better than the rubber I tried (inner tube). The lead worked well enough, I never tried anything after that.
 

Dan

Staff
May 25, 2008
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VelardeJose, I am looking forward to what your friend tells you. The vibration can be a definite buzz kill. I think it would lengthen lifespan to the engines as well. There are a good many folks who ride these inexpensive forms of transportation out of necessity and every bit of knowledge is a good thing.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
241
63
up north now
I noticed on a couple of bikes I've built, the frame angle is off a little. If you fill that area between the mount and the frame with filled epoxy "putty" so the gap is 0 it vibrates less too.

Place saran wrap around the frame, and across the mounts.
Mix up the putty and put the engine in place, tightening only enough to secure the engine and squeeze out enough putty to make sure the gap is gone. Once the epoxy has set up, tighten the rest of the way and trim the excess saran wrap away.

If you use lead sheet like I do, you can bed it into the mount while you do this.
 

Dan

Staff
May 25, 2008
12,775
109
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Moosylvania
I noticed on a couple of bikes I've built, the frame angle is off a little. If you fill that area between the mount and the frame with filled epoxy "putty" so the gap is 0 it vibrates less too.

Place saran wrap around the frame, and across the mounts.
Mix up the putty and put the engine in place, tightening only enough to secure the engine and squeeze out enough putty to make sure the gap is gone. Once the epoxy has set up, tighten the rest of the way and trim the excess saran wrap away.

If you use lead sheet like I do, you can bed it into the mount while you do this.
Swaped a motor from a Khulna to a point beach and it shook twice as much. I'm going to try that, thanks. The angle of the down tube was further away.
 

velardejose

New Member
Sep 9, 2008
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Lima, Peru
Bikeguy Joe
What thickness is the lead sheet you use?
Dan
I visited Mr Morcia, the machinist who does dynamic balancing
He was pleased to see the mb and talked me about single cyl engines
Showed me an old book with drawings that explained this:
The two thirds from the rod closer to the piston+cyl pin+piston+rings weight must match the counterweights in the oposite end of the crankshaft
The rod's third closer to the journal should balance with the rest of the crankshaft
His personal opinion
The piston+pin is too heavy
Lightening it should reduce the vibration
When I told him that the piston skirt blocked the intake he told me to clear it
Then he told me a couple two cycle tips to make the engine have more torque or high revs
Jose
PD He showed me a couple gokart crankshafts, I forgot he sells and repairs them :oops:
 

Dan

Staff
May 25, 2008
12,775
109
48
57
Moosylvania
Bikeguy Joe
What thickness is the lead sheet you use?
Dan
I visited Mr Morcia, the machinist who does dynamic balancing
He was pleased to see the mb and talked me about single cyl engines
Showed me an old book with drawings that explained this:
The two thirds from the rod closer to the piston+cyl pin+piston+rings weight must match the counterweights in the oposite end of the crankshaft
The rod's third closer to the journal should balance with the rest of the crankshaft
His personal opinion
The piston+pin is too heavy
Lightening it should reduce the vibration
When I told him that the piston skirt blocked the intake he told me to clear it
Then he told me a couple two cycle tips to make the engine have more torque or high revs
Jose
PD He showed me a couple gokart crankshafts, I forgot he sells and repairs them :oops:
Great info, thanks. What CC did you show him? I have never had a 50 and wonder if vibration would be less given that information.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
241
63
up north now
I tried lead because in my search for soundproofing a studio I was working on, I found that lead is the best sound deadener there is.

I figured since vibration is sound is vibration, I would damp the vibes with lead.....works EXELLENTLY!
 

old motorbike

New Member
Sep 21, 2008
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I will try to find a close shop that is interested in working on it for a reasonable price.
When I just hold it clutch in and rev it up it gets to an rpm (maybe 3-4000) that the whole bike starts to vibrate, that I believe can be lessened with balancing. I was just looking to see if anyone knew of a shop that did this to these engines.
I use a shift kit to help hold it under that rpm range.
I used to have a lot of (car) race engines and it didn't cost a lot extra to have balanced. Now I work in a bike shop where we have 50cc scooters and even an old honda mo ped and they don't vibrate much for singles.
 

Dan

Staff
May 25, 2008
12,775
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48
57
Moosylvania
I tried lead because in my search for soundproofing a studio I was working on, I found that lead is the best sound deadener there is.

I figured since vibration is sound is vibration, I would damp the vibes with lead.....works EXELLENTLY!

Joe, I thought you were kidding! Makes sense though. And it molds, protects paint. Very cool.