Dong Fang DF 250 RTB Bobber Information

[axa]

Fab them all and do some decent hardening. It won't be a problem for you.

That way, you will kill two bird with one stone - you'll get your studs AND (which is even more important), you'll convince your lady one more time, that those chunks of cast iron named "South Bend" and "Brigdeport" are NOT clogging garage - they are essential for nowadays household.

And don't hesitate to squeeze "Virago's" twin in your DF - it'll be a... "mechanical delicacy".

yes, machining is only a infrequent hobby, but perhaps this bike alone has justified my lathe, and to less extent mill, more than any other single item i own.
to keep this thing running ive made sprocket studs, gear shift linkage, gear shift stud, brake/clutch lever bushings, decked cylinder head, trued cylinder/head faces, various other fittings to mount replacement head/fog lights.

And now a cylinder stud i guess.. but if you read up on these you will find the consensus that home made isnt feasible.
Proper material, treatment and thread formation is out of my capabilities...

- threads should be rolled, i dont have the equipment
- Home brew hardening is vastly inferior to production, (i went through too many home made sprocket studs due to inadequate hardening)

So basically i don't have the experience to know home made will or will not hold up.
Though here seems i don't have a choice, this stud is not sold.

I suppose a good bet and saved time would be a production bolt of same threading, use that on the head side and then cut and thread the bottom side where conditions are less harsh.

Then again i when i get the stud out, I wont at all be surprised to find an unhardened stud with common cut threads...

[axa]

Attachment 19723

Mine is running just fine.

haha, there must be 10 posts on this forum with the same pic of barnone on the 'dragon' posting how fine his bike is running...
i dont know, for all we know it could be broken down under a tarp in the back of his cabin for the last year...

[axa]

ok Zorge here is the first details of said 'mechanical delicacy'; real motorcycle porn if you ask me
Specifically this was done on the heist but its all the same.

mods.jpg

further more as i got the practically new engine for only 375$ USD, it leaves me a budget to pick up the 314cc big bore kit when i get back out to asia...

Hope people recall this number when $600+ for a new 167fmm is tossed around. you are entirely correct, the price for this low performance engine in the US is at least 4x what it should be because there is little to no desire for it.

[axa]

One more thing, when having to change your piston on the 167fmm, note there are interference and non interference fits sold...
In my opinion (and only an opinion cuz ive never had the engine running long enough) the non interference can only shorten life as it is a design for high performance engines that are torn down regularly...

here's a pic, of the two so you at least know what you got even if the people who sold it to you dont
pistons.jpg
notice the oil holes for the gudeon pin

measuring the bore i found it oblong and already out of relative tolerance (relative to the spec the cg 125 defines as there is none available for the 167fmm)

The trouble here is while a 'top tier Chinese' manufacture might be producing the engine, Ive found nearly all if not all of the replacement parts Ive acquired really poor quality.
that said my original engine didn't last 1000 miles either.


also you will find valve spring stiffness night and day between them, i suspect this had something to do with my 2nd engine failure.

[SR.MAILMAN]

If you go with the big bore kit,you will have to bore out the case 2 mm. OEM is 55 mm and the kit has 57 mm sleeves.
Then you will have the problem of feeding it. Forget about any kind of mpg. Horsepower is not free.
I am quoting from 2 people that have done the conversion. They also went with side draft manifold conversion.
One guy used a carb from a 500cc bike. Both had aftermarket exhausts. (drag pipe type).

[barnone]

haha, there must be 10 posts on this forum with the same pic of barnone on the 'dragon' posting how fine his bike is running...
i dont know, for all we know it could be broken down under a tarp in the back of his cabin for the last year...

Just rode it up there today and drew a big crowd as usual. Didn't get a photo but will next time. Just cause you have made a lot of half ass butcher jobs on your DF doesn't mean mine is not running just fine. AXA is now on ignore, much better way to enjoy him. Please do not quote his posts.

[axa]

If you go with the big bore kit,you will have to bore out the case 2 mm. OEM is 55 mm and the kit has 57 mm sleeves.
Then you will have the problem of feeding it. Forget about any kind of mpg. Horsepower is not free.
I am quoting from 2 people that have done the conversion. They also went with side draft manifold conversion.
One guy used a carb from a 500cc bike. Both had aftermarket exhausts. (drag pipe type).

yup, been considering/following this mode for quite a while. and while im not saying id do it this way, ive seen 1mm taken off an oversized 1/8" thick sleeve at the base to get it in the original case bore. nice option to avoids having to crack open the case.

for since no exhaust came with the engine, ill pickup the 2 exhaust headers since they are cheap and fabricating the rest of the pipes.

moving the carb to the side might be nice as well.

And there is always the wide version of this peanut take if i get tired of having to refuel..
should be fun

[axa]

Just rode it up there today and drew a big crowd as usual. Didn't get a photo but will next time. Just cause you have made a lot of half ass butcher jobs on your DF doesn't mean mine is not running just fine. AXA is now on ignore, much better way to enjoy him. Please do not quote his posts.

you see if you quote me you will be forcing barone into seeing what i say, but he is much to sensitive for this so be sure to protect his snowflakiness by going out of your way to remove any info from me.

me, im not that soft, if anyone can tell me what is what and who is who i welcome it, love a debate and use it to build on the backs of giants, improving the easy or hard way.

and when you get tired of hearing about some grumpy old mans sunday drive, you can follow me and read about something cool, or dont, i for one wont tell you what to do, just suggest you dont become a snowflake cuz they melt.

so good riddance barnone, open source in the information age moves on with or without you.

[Zorge]

And now a cylinder stud i guess.. but if you read up on these you will find the consensus that home made isnt feasible.
Proper material, treatment and thread formation is out of my capabilities...

- threads should be rolled, i don't have the equipment
- Home brew hardening is vastly inferior to production, (i went through too many home made sprocket studs due to inadequate hardening)

So basically i don't have the experience to know home made will or will not hold up.

So, basically, you are telling me that you don’t have heat treat furnace and Rockwell tester? No way!

Jokes aside, IMO, you could solve problem with missing stud by recycling some similar diameter old stud. It is already hardened, alright, but I am convinced that carbide thread cutter insert would do the job. Even if you don’t have black belt in cross slide kung-fu and you make generous relief groove, you’ll make more than good enough stud. You can even do the trick by thread cutting with lathe turns in reverse and get spick and span stud.


It’ll hold.

ok Zorge here is the first details of said 'mechanical delicacy'; real motorcycle porn if you ask me

No frame re-tailoring needed – IMO, that’s good portion of job already done. It look to me that also engine is not cramped in the frame, so it won’t te to hard to fit exhaust and carb (on his stock position or this side draft mod you mentioned). In short, this is not the worst engine swap.

One more thing, when having to change your piston on the 167fmm, note there are interference and non interference fits sold...

Did you try to comb some piston manufacturers catalogs? Do some measuring with Vernier and dig in. I’m sure that you’ll find something that fits.

About those oil holes for gudgeon pin... I know that some designers strive to make fit between pin and piston as tight as possible, so all the wobbling when engine runs, happens between gudgeon pin and conrod’s small end (bushing or needle roller bearing, that is).

...So it’s not a big deal if those holes are omitted. After all, if necessary, you can easy drill those holes.

[axa]

So, basically, you are telling me that you don’t have heat treat furnace and Rockwell tester? No way!

Jokes aside, IMO, you could solve problem with missing stud by recycling some similar diameter old stud. It is already hardened, alright, but I am convinced that carbide thread cutter insert would do the job. Even if you don’t have black belt in cross slide kung-fu and you make generous relief groove, you’ll make more than good enough stud. You can even do the trick by thread cutting with lathe turns in reverse and get spick and span stud.


It’ll hold.



No frame re-tailoring needed – IMO, that’s good portion of job already done. It look to me that also engine is not cramped in the frame, so it won’t te to hard to fit exhaust and carb (on his stock position or this side draft mod you mentioned). In short, this is not the worst engine swap.


Did you try to comb some piston manufacturers catalogs? Do some measuring with Vernier and dig in. I’m sure that you’ll find something that fits.

About those oil holes for gudgeon pin... I know that some designers strive to make fit between pin and piston as tight as possible, so all the wobbling when engine runs, happens between gudgeon pin and conrod’s small end (bushing or needle roller bearing, that is).

...So it’s not a big deal if those holes are omitted. After all, if necessary, you can easy drill those holes.

I agree, ill make a stud and expect it will hold, this will make way better go kart engine than motorcycle anyway.

No, there are no catalogs i know of, i have to rely on, in US we have to rely on few online seller and ebay, its a crap shoot.
But my point was the floating pin piston i received was just a poor design, and like u, i notice most all are interference tight fit.
I wouldn't mind an interference fit to have oil holes, i image the aluminum piston expands somewhat more than the steel pin, oil can help any galling.

Again I just reporting the technical detail for anyone who may have the misfortune of trouble with their OEM engine.
Here the outlook is bleaker than I think anyone realizes.