Dong Fang DF 250 RTB Bobber Information

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Originally Posted by barnone

ENGINE COMPRESSION TESTING

http://www.dansmc.com/compression_test.htm

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Thanks for the link, Vince. I'm learning that some of the tools that I never considered should be part of my toolkit. I think that a DMM, feeler guages and compression tester are basics, cost less than $50, and should be on hand almost before you drag out the first wrench or screwdriver.

I do not have the expertise to do so, but it would be nice to post something with a tool list and links to basic usage and maybe specifics for this bike. We used to release a troubleshooting flow chart for all our systems when I worked for TI.

Roadkill,
Your welcome. I almost went to work for TI in 1967 after I got out of the USAF but chose IBM instead. Spent 30 years as a mainframe ( now called the Cloud :lol8:) System Engineer.

If you google 167fmm or CG125 you can find lots of info on the DF engine. These are nice simple bikes.

Attachment 15534
Off to the dump/recycling center with another load.

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Originally Posted by barnone

Roadkill,
Your welcome. I almost went to work for TI in 1967 after I got out of the USAF but chose IBM instead. Spent 30 years as a mainframe ( now called the Cloud :lol8:) System Engineer.

If you google 167fmm or CG125 you can find lots of info on the DF engine. These are nice simple bikes.

Attachment 15534
Off to the dump/recycling center with another load.

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'm an analog guy. Mostly RF/microwave and optical. We both started back when it was all analog and vacuum tubes were the norm? Digital gets the glory, but the world still requires analog I/O.

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Originally Posted by DanDaMan

its a 2 valve pushrod, everything it has is between 2500-5000 rpm , if u drag out more rpms great 4 u beating the soft springs I was givin , if u don't here your valves clicking away , either you geared to low or to tight

and tight = engine death

redline all u want , valve float from pushrod engines stops any poss damage

unless valves to tight ---

and roadkill , that "miss" sounds like u need a valve, like axa but not blown cylinder like him

adjust valves NOW

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This inst exactly true, the push rod design in general having more engine mass than say a ohc, not only limits the rpm in comparison with its greater inertia, but also if allowed to float, increases collision force between components when they finally catch up with each other.
That is under normal operation, all components are at least going in the same direction, when floating finally catching up to each other they collide.

This is why i may never be able to accurately diagnose what the cause of 85highwall and my blow engines were. The common factor is that we both died red while red lining.

Did my rod bend jamming the valve train breaking a valve off, or did the valve drop jamming the valve train bending the rod, ill never know.

but i adjusted and didn't have tight valves, i don't think 85highwall had tight valves either, so as much as it pains me to say it, the only concision i can make from evidence is that engine death for these Chinese clones comes faster due to redlining than it does due to tight valves...
not that tight valves are ever a good idea...

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Originally Posted by bowtiewagon

located a new part online here.
http://www.motopartsmax.com/index.ph...roducts_id/666.

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funny, i had ordered from the same place last week... not via ebay though as they dont sell the parts i want there. else i would have, as ebay will protect you in addition to your credit card...
why do i care? cuz this place has an "F" rating with the bbb.

so we'll see...

on a related note, i did some practice back cutting of the valves the other day, one thing i noticed was they are made from cast steel rather than a rolled steel.

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

You will notice they dont machine the back of the valve, and while some would argue this even helps atomize the fuel air mix, only machining the valve seat edge (and stem of course) it leaves a nasty ridge i cut away with that back cut...

finally did my 1st real oil change , insteada drain stain and pour back in , yes cheap 10/40 car oil , still

slightly tightened valves , and ran 65 all the way to work with a few 70-75 bursts from down hill and drafting runs

if u recall , I did run VERY loose on my valves , I just passed 5500 miles , decided to tighten up , and its improved speed slightly

the hotter It is outside the slower I go , nice cool morning mid 70's

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Originally Posted by DanDaMan

finally did my 1st real oil change , insteada drain stain and pour back in , yes cheap 10/40 car oil , still

slightly tightened valves , and ran 65 all the way to work with a few 70-75 bursts from down hill and drafting runs

if u recall , I did run VERY loose on my valves , I just passed 5500 miles , decided to tighten up , and its improved speed slightly

the hotter It is outside the slower I go , nice cool morning mid 70's

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Dan, can I ask how it is that you (never mind tall tales GARDO and his 90mph down the GSP) are the only person who claims to be able to approach anywhere near 70 regardless of a cold day or down a hill...

Have you ever actually VERIFIED your speed with a GPS or even timing with mileage markers?
Never mind you have a fat car tire and all its surface area rolling resistance...
Dont you ride with a soft 35 or so psi??

i have an engine build in the works, heavy head work, decking, valve shaving, steel rods, and im considering treating the cylinder sleeve... but i only have the slightest hope to be able to "cruise" steady at 60 (which for your information would be 66 indicated)

Did a lot of redlining on this bike, and down hill my engine floated by 7.5k, which with my ratio is 58-59 actual mph.
So even if I had your lower ratio that is still well under 70.
So i would love to know what exactly it is that makes your bike so special...

I wish I knew , I geared for 90 , rear tire size + ratio to determin speed at 6000 rpm's

I wish 1 single person was in Austin so we could go ride together

and yes I have been tailed and verified - although had the smaller front tire , so speedo read 10% faster then = have since added a slightly taller tire to make speedo more accurate , when drafting I can run center lane without slowing traffic

DanDaMan,
Any engine mods?

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Originally Posted by DanDaMan

I wish I knew , I geared for 90 , rear tire size + ratio to determin speed at 6000 rpm's

I wish 1 single person was in Austin so we could go ride together

and yes I have been tailed and verified - although had the smaller front tire , so speedo read 10% faster then = have since added a slightly taller tire to make speedo more accurate , when drafting I can run center lane without slowing traffic

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Lived in Austin for a year or so. I really miss it. In that year, I don't think I hit 60 any place in town. That city has the most messed up drivers in TX except for Laredo. Rode a Honda Valk in Laredo for a while. That's some crazy stuff for a biker.

no engine mods only added bigger mainjet and removed air inject

maybe it is as simple as that , gearing for 90 , so your 4h gear will be AT LEAST as fast as 5th was stock

let me break it down , when I got it top of 5th did about 60 screaming , I got the 13 tooth front (10% speed increase every front tooth = 20 %) that got me near 72 screaming , then I dropped in the 35 rear (2% per tooth) nuther 20% about 86 mph for screaming valve float rpm's

- but actually 5h only does like an overdrive gear holds highway speed at low rpm's , unless I can get rpm's up a bit (catching a short draft backwind or downhill stretch) , then baring an uphill stretch or stiff headwind it will hold the higher speeds unaided to about mid 70's

=now 4th reaches slightly taller than 5th did stock about 60-65 when shift to 5th

I also have the lower mass 428 HD chain , which allows for more drastic front sprocket change

and im not yanking chains , I wish someone wer near to verfy , what im able to get from her , simply by making it basically a 4 speed (to 65mph) then a overdrive gear (5th) that has very little power other than to HOLD SPEED that 4th gear attained , at low nice sounding rpm


haha - shoot I even have a 2X8" speaker cabinet that tops my sissy bar and acts as my backrest , with plug play quick disconnects for lighter outlet to power mp3 player , phone recharger and amp power - working but still a work in progress

Does anyone know how to tell when I need a valve job? My bobber is getting a tinging pinging noise and seems to have more vibration than normal. It has almost 3k. And if it does, is there a tutorial to learn how to do a valve job? Thanks!

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Originally Posted by Tedub

Does anyone know how to tell when I need a valve job? My bobber is getting a tinging pinging noise and seems to have more vibration than normal. It has almost 3k. And if it does, is there a tutorial to learn how to do a valve job? Thanks!

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Check link 5067 posted by Barnone. Compression testors are pretty cheap.

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Originally Posted by DanDaMan

no engine mods only added bigger mainjet and removed air inject

maybe it is as simple as that , gearing for 90 , so your 4h gear will be AT LEAST as fast as 5th was stock

let me break it down , when I got it top of 5th did about 60 screaming , I got the 13 tooth front (10% speed increase every front tooth = 20 %) that got me near 72 screaming , then I dropped in the 35 rear (2% per tooth) nuther 20% about 86 mph for screaming valve float rpm's

- but actually 5h only does like an overdrive gear holds highway speed at low rpm's , unless I can get rpm's up a bit (catching a short draft backwind or downhill stretch) , then baring an uphill stretch or stiff headwind it will hold the higher speeds unaided to about mid 70's

=now 4th reaches slightly taller than 5th did stock about 60-65 when shift to 5th

I also have the lower mass 428 HD chain , which allows for more drastic front sprocket change

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If u say so, I can't have all the facts to say otherwise, but I do think I have most of the facts.

As for the chain discrepancy, I understand there is justification:
http://www.superstreetbike.com/how-t...er-mythbusters

But the benefits are so miniscule I just don't see it... And ones that I would think surely eaten by a FAT car tire!
I'm more inclined to consider an improvement in chain quality over stock a more significant factor.

So has anyone seen a performance increase when ditching the stock chain for something better? Let alone performance increase with any chain swap at all?

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Originally Posted by axa

If u say so, I can't have all the facts to say otherwise, but I do think I have most of the facts.

As for the chain discrepancy, I understand there is justification:
http://www.superstreetbike.com/how-t...er-mythbusters

But the benefits are so miniscule I just don't see it... And ones that I would think surely eaten by a FAT car tire!
I'm more inclined to consider an improvement in chain quality over stock a more significant factor.

So has anyone seen a performance increase when ditching the stock chain for something better? Let alone performance increase with any chain swap at all?

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I did see a post where someone had switched to larger front sprocket and 35T rear. They did the chain swap because of clearance problems with the larger sprocket. There is a kit being sold for Tha Heist. I think it's about $100.

I didnr realize there was proof to smaller chain - better hp+torq , I thought it mearly the fact I was gearing 20% higher that any o u could was the issue :p

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Originally Posted by DanDaMan

I didnr realize there was proof to smaller chain - better hp+torq , I thought it mearly the fact I was gearing 20% higher that any o u could was the issue :p

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Didn't say that. Smaller chain from what I read was only for fit. I think it was to clear the front cover with the larger sprocket. Seemed like to much work for me so I stayed with the 35T rear sprocket mod. I'm pretty sure that you could gear a bicycle to go 150 mph if you could pedal it. I don't think I would like the acceleration of this machine if the ratio went any higher.

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Originally Posted by DanDaMan

I didnr realize there was proof to smaller chain - better hp+torq , I thought it mearly the fact I was gearing 20% higher that any o u could was the issue :p

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Yes the lower ratio would in theory allow a higher speed of travel, by moving ceiling created by float at around 7.5k
But one needs the engine power to overcome all resistances (primarily wind at highway speeds) to attain these higher speeds.
And if one considers a flat road with windless conditions as a benchmark, none of us other 167fmm riders have seen enough power to "cruise" at the speeds that you claim to...

Thus the search for what is so unique about your bike goes on...

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Originally Posted by Roadkill

I did see a post where someone had switched to larger front sprocket and 35T rear. They did the chain swap because of clearance problems with the larger sprocket. There is a kit being sold for Tha Heist. I think it's about $100.

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Right, it was Dan.
But you can get the same parts far less $ than that. Everything on that site is way over priced.
They sell decked cylinder heads for $550 for xst sake ...

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Originally Posted by axa

Yes the lower ratio would in theory allow a higher speed of travel, by moving ceiling created by float at around 7.5k
But one needs the engine power to overcome all resistances (primarily wind at highway speeds) to attain these higher speeds.
And if one considers a flat road with windless conditions as a benchmark, none of us other 167fmm riders have seen enough power to "cruise" at the speeds that you claim to...

Thus the search for what is so special about your bike goes on...

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Little confusion here. I'm roadkill and I've never had mine over 55 mph.

I didn't change chains , I drive a different model , with diff chain

and I think y the higher attainable speed , is simply because no one else has DARED/or botherd to gear for 90, and accepted just the 35 tooth rear as max , which is 60ish with motor screaming , like wants to explode (might varv wih your larger tire)

u need a additional 10-20% (front sprocket) depending on lbs. , im 165

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Originally Posted by Roadkill

Little confusion here. I'm roadkill and I've never had mine over 55 mph.

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That's exactly my point... Dan claims he can attain up to 75.
Truthfully i can't see that, but I'm in pursuit for the most powerful 167fmm possible

even barnones 45 to 30 swap (right?) was/is only a 30% boost to stock

mine has been faster than 60 , since 8 days after it arrived and I maxed front sprocket

yes up an incline or stiff headwind and nothing to draft 60 still my max ,,, in 4TH gear


IMO , you cannot possibly attain that which u have already givin up be4 u started , by gearing so low

if you've geared for 75 even down hill you will never pass that speed as valve float will actually engine brake u preventing more speed EVER from being attainable

gearing really high has drawback being really hard on valve train

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Originally Posted by DanDaMan

I think y the higher attainable speed , is simply because no one else has DARED/or botherd to gear for 90, and accepted just the 35 tooth rear as max , which is 60ish with motor screaming , like wants to explode

u need a additional 10-20% (front sprocket) depending on lbs. , im 165

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Barnone used a 2.30769231 ratio and I believe went back to 2.69 for the same lack of power reason I just posted.

Dan, I'm going to give you the benefit of the doubt on both the higher ratio and smaller chain...
But do u realize you are claiming such a massive amount of better performance than absolutely everyone else gets that it is just hard to believe.
Really I'm not looking into getting into a pissing match about this but that GARDO creep spread allot of bull shit about this bike that helped influance me to buy it. I may not have otherwise...
and I just think the true potential should be clear, not subliminal wishes...

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Originally Posted by DanDaMan

I didnr realize there was proof to smaller chain - better hp+torq , I thought it mearly the fact I was gearing 20% higher that any o u could was the issue :p

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About a one percent improvement in that test the axa showed us. That is not going to make much of an improvement in speed.

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Originally Posted by axa

Barnone used a 2.30769231 ratio and I believe went back to 2.69 for the same lack of power reason I just posted.

Dan, I'm going to give you the benefit of the doubt on both the higher ratio and smaller chain...
But do u realize you are claiming such a massive amount of better performance than absolutely everyone else gets that it is just hard to believe.
Really I'm not looking into getting into a pissing match about this but that GARDO creep spread allot of bull shit about this bike that helped influance me to buy it. I may not have otherwise...
and I just think the true potential should be clear, not subliminal wishes...

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I just assumed that Dan was talking about the bobber, but his recent post says that he drives a different bike. Maybe it's lighter, or has a different transmission. Might be his will do what he says. Don't they make s streetbike version with the same motor?

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Originally Posted by DanDaMan

yes up an incline or stiff headwind and nothing to draft 60 still my max ,,, in 4TH gear

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This is what I'm talking about...
If my heavy head work achieve 60 on just a flat.... Ill die happy.
Ur extremely lucky. Apparently no one else comes close.

I agree axa a fat man buying this isn't gunna race the highways at 70 , I am 165 and its not usual to get perfect circumstances , but 60 attainable and sustainable , with bursts +15 depending on heavy driver and conditions

same carb , engine , tranny , electronics , brakes = neck angle , diff chain and sprockets the only real diff

who lives close to Austin ill ride to u, I was even thinking about riding to SCarolina , visit my bro/family