Dong Fang DF 250 RTB Bobber Information

[barnone]

axa,
I agree with you about engine swaps however I keep looking for a CG400.

0407151506b.jpg

Remind me how much you milled off the head?

[ben2go]

I've already measured up a DF250 for a GS500 engine.It's a bit tall but could be made to work.It's more work than I want to do tho,unless I found one for peanuts.

[axa]

axa,
I agree with you about engine swaps however I keep looking for a CG400.

you will never find it.

axa,
Remind me how much you milled off the head?

yikes, thank god i write things down, seems i recall taking off 35mil for a 10:1 ratio not 10.5 as i posted... that would require 50mil off. i really want to try that but when you have a bike running nice, one gets complacent.

Note 20mil would actually only bump to 9.5, though on this very forum one guy defending gardo in an argument with you barnone, mentioned 20 would take it higher...

here are the notes

by the way, that was a vid of my practice run on the blown head... i have vid of the head in use somewhere...

[axa]

http://clevelandspeedshop.com/collec...ton-gasket-kit
$419.95
Bore 69.5mm - Stroke 65mm = approximate 247 cc

Stock is 67mm x 65 = approx. 229 cc

gain in displacement is about 18 cc

interestingly enough i tracked down the manufacturer of this piston, and the 'customer' who requested it was some garage in the vicinity of ccw i believe.
but the funny part is i learned there was only perhaps a single order of perhaps the minimum of 4 pieces ever made... at least at that time... but i couldn't get them to sell me one even if they had made any more.

That said i really would love to get my hands on a half over piston.
id try boring out the original cylinder that i had the dropped the valve a valve and see the impact
again though from what ive learned, its more about the compression at this scale... but cant say for sure until its attempted

Maybe there is an increase in compression ratio.

that's another interesting note, on the box they got wiseco to print something like "compression ratio 11:0"
(there was a better picture at somewhere at sometime)
Of course there is no way for a piston alone to determine the ratio, but you can have them print anything you want on your box...
and knowing ccw dubious claim history, i am doubtful of that spec
Not that it couldn't be done. You could easily raise the gudgeon pin hole center easily.
Or increase the dome of the piston which would take more careful planning.


anyway a mass of wasted money for 18cc and a shady promise of higher compression.
hmmm, maybe i should start a head decking service... 50$ including return shipping in the US 48 seems reasonable...

[barnone]

[QUOTE=axa;75060
hmmm, maybe i should start a head decking service... 50$ including return shipping in the US 48 seems reasonable... [/QUOTE]
I'll be your first customer. I won't be in WNC where my DF is resting until early May.
What octane fuel is required for the increased compression ratio?
Just leave the valves in the head? Just need a new head gasket?

[axa]

I'll be your first customer. I won't be in WNC where my DF is resting until early May.
What octane fuel is required for the increased compression ratio?
Just leave the valves in the head? Just need a new head gasket?

call me cheap or call me poor but just reused the same head gasket that the engine blew with. I didn't see anything wrong with it.
Its a typical metal head gasket, and while i am sympathetic in the science of the proper crush of a new gasket, I don't believe it matters on this kind of low precision engine.
I just reassembled with carefully applied rtv silicon.
That said you can get a gasket on eBay for not too much if yours didn't come off well.

I should mention I ported the new head while i was at it. I can't rule out the impact that might have on performance as well.

[axa]

sometimes I fell I'm rolling on a time bomb.



the remains of another blown engine from a 2010

[SR.MAILMAN]

i can attest as soon as you start considering motor swaps, you start considering bike swaps.
Not that it cant be done, and not that it hasn't been talked about to exhaustion, but fact is more have ditched this bike, then ive ever seen ditch the motor...

A. information on guaranteeing one of the other cg or cb engine clones are a bolt in replacement is scarce. You will need your motor in hand and measure.
B. then you also need to acquire the pipe, carb, so on and so-forth. Which is not usually not worth the price on a $2k bike.

Then as i mention, you start realizing if your willing to do the mods for motor swap above, its not a far to stretch to mod a lightly used Japanese cruisers which can be had at similar prices.
Been down all of these paths.

Truth be told if looking to just maintain speed, turns out for me at least, decking the head was the least amount of time, work, money.
Got a video of it here. 5 minutes of my life.
Sounds strange now that i think about it, a simple head deck...

Best advise for newbies... All though I understand the challenge to improve/modify an existing machine.
A used Japanese 250 ( over 20 years with same engine) would be a better investment, for a commuter that needs to hold highway speeds.
If you were to bore the crankcase out 2mm... This big bore kit would make it a real "sleeper".

334cc Big Bore Kit!

This had NEVER been offered anywhere, for any price. Leave it to ScrappyDogs to get this on the market. Set of 55mm big bore cylinders with matching pistons and rings for the XV250 type engine found in the yamaha virago, Vento V-thunder, Vento Colt, Diamo Cruiser, and many customer small bore choppers that have been made for years. Get the extra grunt and oomph you need! $599.95 for a complete set of front and back top end kits. Forged piston kit available by special request and order. Add 100 dollars for forged option.

[axa]

Best advise for newbies... All though I understand the challenge to improve/modify an existing machine.
A used Japanese 250 ( over 20 years with same engine) would be a better investment, for a commuter that needs to hold highway speeds.
If you were to bore the crankcase out 2mm... This big bore kit would make it a real "sleeper".

First you speak of good ole Japanese bike, then talk suggest putting not as good new Chinese hardware on it?
Not sure you can have it both ways.

Well i suppose if you had something with high mileage/motor abuse to rework...

A while back I did see this vendor put one of these big bore kits on ebay. It had a cracked fin and was priced cheap...
I searched for cheap old vx250 for days after... no dice

[SR.MAILMAN]

Remember when anything made in Japan was crap ? I hate to say this but... China is catching up, if not slowly.(not all products)

Rumor has it that some Japanese small bikes/ parts are made in China under license.

I know of one person that did the big bore upgrade and once He got the crankcase bored out
the only problem he had was the proper maximum carb jetting. ( He had switched to a side draft carb)

Maybe when the Dong Fang has been around 20 years... their will be better/bigger parts out there.