Dong Fang DF 250 RTB Bobber Information

**barnone** · 10-12-2011, 10:28 PM

I got the tiny and very light weight new battery installed and she fired right up. http://www.batterystuff.com/powerspo...09A2-BS12.html
Amazing technology with those lithium batteries.

Took her out for a "high" speed run. At 75 MPH indicated (probably about 68 MPH real) she is turning (with my 38 tooth rear sprocket) about 7600 RPM in fifth.
Vibration is getting very uncomfortable at that RPM.

**hooliganboy** · 10-13-2011, 04:37 AM

i had my bike out on the highway yesterday and the vibratons were pretty uncomfortable around 50mph, but i'm still running the 45 tooth sprocket. i ordered the 35 tooth from oldbikebarn today, and as long as i can cruise comfortably around 55 i'll be satisfied.

**bowtiewagon** · 10-13-2011, 04:30 PM

o.k. ya'll have my curiosity peaked.. what causes the vibrations? if you can pin point it.. or even a rough best guess.

**Gardo** · 10-13-2011, 04:55 PM

Originally Posted by bowtiewagon

o.k. ya'll have my curiosity peaked.. what causes the vibrations? if you can pin point it.. or even a rough best guess.

Oscillation of the motor, dont think the DF is counter balanced . Sitting in the hard mount and as the thumper moves it causes a vibration to reverberate through the frame. The oscillation will hit a certain frequency which will vibrate the bike in the higher RPM range

**bowtiewagon** · 10-13-2011, 05:56 PM

wow thats pretty interesting..is there a sort of dampener to attach to the frame mounts where the motor sits that would lessen the vibration? I am assuming that it gets worse at higher RPM's and higher speeds...

**barnone** · 10-13-2011, 09:17 PM

I believe all CG250 (167FMM) have a balance shaft which is an eccentric weighted shaft which offsets vibrations in engine designs that are not inherently balanced like the one cylinder engines in the DF and the Heist.

The CG250 is a enlarged clone of the Honda CG125. The CG125 was designed by Honda in 1950 so it's not the latest and greatest in technology.

CG125 balance shaft assembly

Anyway, I feel that the vibration is not a problem with the DF engine since it starts occurring at 7500 RPM which is where the power drops off on these push rod engines. I didn't experience this vibration until I started testing with my mini tach. I need to go to a 35 tooth rear sprocket to reduce the RPM at 75MPH indicated.

**barnone** · 10-13-2011, 09:19 PM

Originally Posted by Gardo

Oscillation of the motor, dont think the DF is counter balanced . Sitting in the hard mount and as the thumper moves it causes a vibration to reverberate through the frame. The oscillation will hit a certain frequency which will vibrate the bike in the higher RPM range

Gardo,
It's not a counter balance, it a balance shaft. And the Heist and the DF engines are 229cc not 250cc.

**bowtiewagon** · 10-13-2011, 10:59 PM

excellent information Thank you.
I have a question on a bit of another topic. Does anyone know if the stock handle bars on this bike is 7/8 or 1 inch. I am looking to change mine but everytime I try to do a measurement I am unsure and do not want to get messed up. thanks.

**barnone** · 10-13-2011, 11:34 PM

Originally Posted by bowtiewagon

excellent information Thank you.
I have a question on a bit of another topic. Does anyone know if the stock handle bars on this bike is 7/8 or 1 inch. I am looking to change mine but everytime I try to do a measurement I am unsure and do not want to get messed up. thanks.

7/8" handlebars on the DF.