Dong Fang DF 250 RTB Bobber Information

**ben2go** · 10-05-2013, 03:16 AM

Originally Posted by axa

What a coinkidink, today i made the trek across the street to the veteran machinist at my day job, and that is precisely what he suggested i consider instead.
After talking it out it he seemed to confirm my suspicion that will be very difficult to find the right components to make the bore work...

First of all I cant find a CG piston that is wider than the stock ~66.5mm we have already... Then when I match it with another model, the wrist pin is often a different size than the 16mm required. Then i have to conciser matching the connecting rod... so on and so forth... Ive taken on too many projects like this, got to learn to be realistic.

Though we determined the real deal breaker is that there is no good way to know how much material needs to remain on the cylinder body or other components after machining to not fail.
Having an engine seize on me wont be a good way to find out...

I'm going to speak to the engine shop once more to confirm, but even if they are willing, i wont be a good price.
They wont likely be able to find anything i couldn't, wont be able to just order a a kit, the price will go through the roof.

Therefore it seems that a head job, port matching, cleaning the casting, and some polishing may have some potential on a very likely poorly machined Chinese engine.

And if there is any enough clearance, i will mill the head down.
Do you or anyone, happen to know how much, if any extra head clearance there is on our version?

Well,I've done this a few times.Find the over size piston with the proper spacing from wrist pin center to crown, but with a smaller pin diameter.Then offset machine the wrist pin journal in the piston to except the larger original pin.It increases compression and will require a deck height check and cc the head to make sure the piston and valves don't hit, and the CR isn't to high.A thicker cylinder base gasket will make up the difference,if it's to much or if piston valve contact will occur.I have also had teflon wrist pin keepers machined instead of using circlips.The last engine I done this way cost me $120 in machining and $200 for parts.It was on a go kart engine I saved from the scrap pile.I don't know the engine make or model.It was older and could have been yamaha or honda knock off.

**barnone** · 10-05-2013, 03:50 AM

axa,
I did find this in the Heist thread but do not know if the information is accurate.
By SSR22925

"The compression ratio on the 167FMM-M is 9-2.1 and will run fine with 87 grade Petrol. If the head is milled .025" it will raise it to 10.5, if there is enough clearance and it is milled .050" it will bump it up 2 full points. Anything above 10.5 and you should run 93 Octane Petrol. At that point you may also want to invest in a variable CDI one with a potentiometer so you can adjust the spark curve if need be to prevent the dreaded sound of engine knock"

**axa** · 10-05-2013, 06:09 AM

Originally Posted by barnone

axa,
I did find this in the Heist thread but do not know if the information is accurate.
By SSR22925

"The compression ratio on the 167FMM-M is 9-2.1 and will run fine with 87 grade Petrol. If the head is milled .025" it will raise it to 10.5, if there is enough clearance and it is milled .050" it will bump it up 2 full points. Anything above 10.5 and you should run 93 Octane Petrol. At that point you may also want to invest in a variable CDI one with a potentiometer so you can adjust the spark curve if need be to prevent the dreaded sound of engine knock"

You know that poster SSR22925 is very curious indeed... He posts twice, both times with immense detailed to explain something, and disappears to never be heard from again...
And get this, this 'Weaver Rides' is in West Berlin NJ, just outside of Philly, guess where SSR22925 states they are from... dare I say this is no coincidence.

**axa** · 10-05-2013, 08:58 AM

the creator comes through again.
Funny cuz i just ran through that entire Heist thread, 1600 posts searching for info. Well skimmed really, cuz not to sound like a douche, after a while its the Weaver mod this and the secret that, and all of a sudden they are riding at 90mph.

Ok so from what i could gather regarding performance, these 'secret' mods consist of, and im paraphrasing a list outlined in that thread:

1 gearing (sprocket ratio)
2 exhaust pipe
3 Carb
4 head work

- changing the gear ratio is a given.

- the exhaust likely just allowing the engine to exhale better. not an expert here but i dont gather a 4 stroke can benefit from a tuned pipe or something. but again, no facts.

- Now the carb from what i could gathered is just bumping the main jet to 105, and 45 pilot. That too is backed up by what is listed on the ccw page for their 'racing' carb... good grief...

But gardo himself reports in this vid he got a "new bigger carb 32mm'... again absolutely nothing to back that up, no model # no indication how It was done, never any convincing detail... but here is a pic showing its likely still the stock pz30 type Keihin clone with the accelerator pump on the side:
red carb.JPG

all indications so far its just more BS.

And then finally theres the head work... now at least there is something to back it up this regarding the decking and compression ratio from SSR22925.

Update: But here you can see its just a standard machined face for the intake, no indication if the bore was made any bigger:
port intake.JPG

I would imagine they took the time to do the casting clean up and some polish as well... a simple job.

What I will do also is take a look at the cylinder and see if it could use a hone.

Well there you have it... now perhaps these guy doesn't want this info to get out in fearing losing a good thing... I mean these guys are paying an arm and leg for this stuff...
Check these prices out from the heist thread:

evap kit $55 ( what can this possibly be? a metal plate, and a stem cap??)
carb mod $140 ( i dont buy this is more than an up jet there is little room to enlarge the throat. Ill try but doubt it)
G&D long $225 ( well i don't know what exhausts go for, but that seems steep)

Anyway, lots of hype and buzz words used in that thread, but limited detail.
Though when this is the attitude:

"I think that i am one of the very few that he (weaver) shared his lil secrets with but what a difference in performance it made on the bike"

Well after $6000 maybe I would too feel i should exaggerate the results.

When i do the work this winter, ill be posting details, pics, and a vid at least of the milling...
I'm sure some of you will get a kick out of it as much as i would...

**axa** · 10-05-2013, 09:07 AM

Originally Posted by ben2go

Well,I've done this a few times.Find the over size piston with the proper spacing from wrist pin center to crown, but with a smaller pin diameter.Then offset machine the wrist pin journal in the piston to except the larger original pin.It increases compression and will require a deck height check and cc the head to make sure the piston and valves don't hit, and the CR isn't to high.A thicker cylinder base gasket will make up the difference,if it's to much or if piston valve contact will occur.I have also had teflon wrist pin keepers machined instead of using circlips.The last engine I done this way cost me $120 in machining and $200 for parts.It was on a go kart engine I saved from the scrap pile.I don't know the engine make or model.It was older and could have been yamaha or honda knock off.

Well perhaps when the engine is off this winter Ill look at it again, but I didn't find it very promising given i cant confirm any specs or measurements for our Chinese clones.

Still the deal breaker will seem to be that no one can tell me with certainty how far, if any, i can bore without compromising the integrity of the cylinder... Ive been able to estimate the material and theres not too much between the current sleeve and bolt holes.

Plus, I just skimmed the entire Heist thread, there was talk that a 300cc bore was being worked on by Weaver Rides but never transpired.
Not a good indication that a bore is worthwhile or even possible on a 167fmm.

**bowtiewagon** · 10-05-2013, 11:25 PM

O.k. Guys, I put the sprocket on with the correct parts and I would like someone to look at this video I made of an Issue I am having.
Big question is... should my chain be replaced after you watch this video you will understand what I am talking about. I left info about my problem in the description of the video.
http://www.youtube.com/watch?v=nO0G2...psMsFWsy8LrB8Q

The wheel rolls true and straight, and freely, until I attach the chain ... in case your wondering.

**ben2go** · 10-06-2013, 01:03 AM

Originally Posted by bowtiewagon

O.k. Guys, I put the sprocket on with the correct parts and I would like someone to look at this video I made of an Issue I am having.
Big question is... should my chain be replaced after you watch this video you will understand what I am talking about. I left info about my problem in the description of the video.
http://www.youtube.com/watch?v=nO0G2...psMsFWsy8LrB8Q

The wheel rolls true and straight, and freely, until I attach the chain ... in case your wondering.

Two things I see right off:1) The chain has some stiff links that is causing it to appear to change route as it rolls over the sprocket. 2) The chain has unevenly stretched also compounding the tracking problem. I would replace the chain with a quality O ring chain with the highest strength rating I could find.Even tho the bike doesn't have a lot of power,it's still trying to pull a full size person plus it's own weight.

**ProDigit** · 10-06-2013, 02:25 AM

I would think it's possible that the wheel is not mounted perfectly straight, and the sprocket is scraping the chain.

It'll wear off over time, but try to make sure you got:
a- 2" chain play on the bottom, and see if the wheel stops as fast or rolls longer when adjusting the horizontal position (chain tight or loose).
b- play around with both wheel adjusters (to tilt it left or right), with the nut of the rear wheel axis loose, and see if the noise gets reduced.

**axa** · 10-07-2013, 02:08 AM

Originally Posted by bowtiewagon

O.k. Guys, I put the sprocket on with the correct parts and I would like someone to look at this video I made of an Issue I am having.
Big question is... should my chain be replaced after you watch this video you will understand what I am talking about. I left info about my problem in the description of the video.
http://www.youtube.com/watch?v=nO0G2...psMsFWsy8LrB8Q

The wheel rolls true and straight, and freely, until I attach the chain ... in case your wondering.

I'm going to give you the benefit of the doubt and assume you made sure your wheel and rear sprocket is in aliment with the front sprocket. Anyway your problems would be more consistent if misalignment was the sole issue.

Also I have never found any evidence that 'play' or slack in the chain of hard tail (or any other rigid machine for that matter) is of any benefit than to have a chain that is taut (not tight).
Besides, thats exactly what a chain tensioner does, takes all play out.

When is the last time you heard someone had a problem because their benz didn't have enough 'slack' on the timing chain...

That said, Occam's razor bro, didn't you say you 10k, rain or shine, miles on that Chinese, o ring-less, stock chain?
Unless you have been servicing it like every 1k miles or so, id would be more surprised if it had NOT worn out by now.
I have gotten 30k out of a quality o ring chain that only saw a dry day on the street, but this is not your case.

You will know the chain is worn if you remove it, lay it out on the floor, pick it up by one end, shake it.
A chain that is not worn is fluid and will bend consistently and smooth. And will be stiff and quiet when you shake it side to side.
One that is worn will be clunky, inconsistent. And will make rattling noises when shaking side to side...

Taking it off also allows you to measure how much it has stretched. Lay it out, compress each link, make a mark at the end. Pull the chain extending all links, make a mark. Measure between the marks and divide that by either total length compressed or extended (either is close enough). That number shouldn't be more than 2%

I suspect, yours will easily show signs of wear.

**bowtiewagon** · 10-07-2013, 02:00 PM

Seems that the general consensus so far is that the chain needs to be replaced. I am going that route at this time. The wheel is straight with the front sprocket, I checked all that,
My next question is what is the size of this chain again, I do not remember.. I remember a 512 or something like that. Thanks.