Dong Fang DF 250 RTB Bobber Information

[ben2go]

wow, looks relativley simple enough. i will give it a shot. Thanks. I am not a motorcycle mechanic, I have more experience with small block chevy's. but I am mechanically inclined.

You're welcome.If you've been inside a SB Chev,this shouldn't be to hard.

[axa]

Just for a couple of references would anyone know where I could find a replacment engine if needed? Add to that a how to on doing the charge rotor. I am pretty much on my own with this thing except for all the input that y'all give..which is greatly appreciated. But..I am looking at the cost of everything involved. Options are always a good thing ya know.
Basically my wife asked me what a new motor would cost seeing as how this one has over 11,000 miles on it. I know they do not last forever. Thanks.

http://www.mychinamoto.com/forums/sh...ll=1#post69259
come on bro keep up on ur feeds...

ill bet thats the best deal you will find, price-wise, as well u get a kick start to boot...
i almost envy u...

but seriously, just google cg250, or 167fmm engine and you will start to find all sorts of stuff...

if you do indeed find that starter clutch the problem , let me know and ill send u a link if this is it:

but try to find the exact problem first before doing anything, because then you will most likely be able to fix it, or find someone who can fix it, or in the worst and rare case be sure u actually need a new engine...

[DanDaMan]

bowtie if engine spins , spray in carb cleaner , if it fires its your jets

5 min to pull n clean


in my news , built oversized fender brackets to accomidate larger front tire , making speedo near dead accurate , runs 60 into a headwind , had it HOLDING 75 on way to work this morning (drafting wind at my back flat roads)

did tighten down intake valve , but axa's problem has me wanting to loosen it again :p

bit over 20 in 1st ,about 40 I second , 55ishin 3rd , 65 in 4th , 5th to near75 with engine turning fast but not screaming , I am 165 lb's

[Roadkill]

Well, my compression tester came in today. Does any one know the actual compression range for this engine? I don't need the compression ratio but the actual compression in pounds.

[axa]

Well, my compression tester came in today. Does any one know the actual compression range for this engine? I don't need the compression ratio but the actual compression in pounds.

funny you ask, i think ur as unlikely to get an accurate compression range as you are to get an actual compression ratio... I firmly believe none of which was every actually measured, but rather passed down from the original honda cg design and inherited from one poor translation to another...

[axa]

So ive finally got around to looking into decking the DF head for the increased compression ratio...

Just received a graduated cylinder in the mail and ill first measure the ACTUAL compression ratio of these things...

That word actual cant be stressed enough, cuz if you look hard enough you will find ratios of 8.7 to 9.5, and everything in between...
This will then give me an of how much to shave off the new head.

Unfortunately I had to get rid of my home mill, it was just too small and inadequate, and since im now banned from our shop at work thanks to OSHA, im going to have to do this on my home lathe...

Set up the old trashed head for a practice run
https://drive.google.com/file/d/0B-M...it?usp=sharing

I dont think anyone would bother decking a cylinder head on the lathe, balancing it alone is a bitch. But here i am, in practice im sure it can be done effectively.

[culcune]

Just for a couple of references would anyone know where I could find a replacment engine if needed? Add to that a how to on doing the charge rotor. I am pretty much on my own with this thing except for all the input that y'all give..which is greatly appreciated. But..I am looking at the cost of everything involved. Options are always a good thing ya know.
Basically my wife asked me what a new motor would cost seeing as how this one has over 11,000 miles on it. I know they do not last forever. Thanks.

These engines aren't as easy to come by as replacements as they used to be back in the mid-2000s (i.e. ebay, etc). One suggestion is to look at your local Craigslist since you live in a major metropolitan area, and put in search terms like Apollo, Apollo 250, Zongshen, Zongshen 250, etc. There seem to always be people asking low prices on Chinese dirt bikes. Most enduros come in 200cc, but many, if not most, of the full-size pure dirt bikes, such as the fairly common Apollos, come in 250cc size (ok, 223cc or 229cc). Apollo use Zongshen engines, and many ignorant bike owners list 'branded' bikes, like Apollos, as 'Zongshen' because that is what the engine states. Either way, it is a good place to start to look because you can generally still part out the rest of the bike, or sell the rolling chassis while keeping the engine.

[Roadkill]

funny you ask, i think ur as unlikely to get an accurate compression range as you are to get an actual compression ratio... I firmly believe none of which was every actually measured, but rather passed down from the original honda cg design and inherited from one poor translation to another...

I thought that would be the case. I'll check mine soon using the same procedure you use on your stock head and at least we'll have a sample of 2. Let me know how you do it when you do yours? Don't know if I should hand turn it for max at TDC or just turn the starter and get a couple of cycles.

On another note, I mentioned that a PU truck cut a left corner short and put me down. I just noticed that the lower bar clamp was loose from the triple tree, (springer version) The fall must have broken the head off of the mounting bolt. I've cobbled it back together using one of the cap bolts for the top clamp. Problem is that the lower clamp bolt is a special deal that isn't listed in the parts book. Anybody out there know how to find one?

[axa]

I thought that would be the case. I'll check mine soon using the same procedure you use on your stock head and at least we'll have a sample of 2. Let me know how you do it when you do yours? Don't know if I should hand turn it for max at TDC or just turn the starter and get a couple of cycles.

Im not actually looking to measuring the compression, just the ratio. Unless i find it a problem anyway...

you will need to turn it over with the starter a few times to build up pressure to peak...
i dont think you can do that by hand, though might be able to do it by kick if we had one...
anyway, i bet google can tell you all you need to know about that

[axa]

and though i probably should have measured the actual ratio on a new head first, i did the practice cylinder head decking removing .025.

https://drive.google.com/file/d/0B-M...it?usp=sharing
i have video of it i might upload if anyone is into machine porn like me...

in theory this would bring the ratio up to somewhere around 9.7, depending what ratio you think you are starting with.

next i will get some play-do and do an interference test...


I will also back cut the valves, as well as port the new head.
i know ive said in the past I didn't believe there would be much to gain in doing this on a 167fmm, but after closely looking at the head in hand, there are some notable defects....

it might be hard to see but, this lip behind the intake valve seat. This is considered a bottle neck and high air flow location, where all the intake air is crammed into a small port before getting into the chamber, in theory it needs to transition better than this.

https://drive.google.com/file/d/0B-M...it?usp=sharing

i bet every head is different though.