Dong Fang DF 250 RTB Bobber Information

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Originally Posted by barnone

9.0:1?

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we have a winner.
your uncanny barnone.

So i must say, i didn't expect it but, indeed the CR we read for the loncin 167FMM is indeed as advertised.

So here is the rundown.
Measuring with a liquid displacement method. really there is no other feasible way:
https://drive.google.com/file/d/0B-M...it?usp=sharing

I didn't ignore the givens and actually measured the stroke at exactly 65mm and bore 67 indeed... The rest was:

Bowl 22cc = 22000ml³ (second take 22.2cc)
TDC to deck 2mm = 7051ml³
Gasket 1mm = 3526ml³
Piston dome 4cc (maybe 5cc)= -4000ml³
Stroke 65mm = 229167.404
229167+22000+7051+3526-4000:22000+7051+3526-4000
(229167.404+28577)/28577
= 9.02 CR

when i double checked a second measure of the bowl, i got the a hair over the graduated measurement line so if you call it 22.2 you get
= 8.96 CR

so it seems that the CR is indeed 9.0

BUT, It was very difficult to measure the piston with the molding clay i had on hand, it was much too hard and didnt conform to the dome and valve relief profile well, and didnt provide a deep enough void. So i estimate i may be a bit wrong on that measurement.
If the numbers are rerun for say a 5cc dome, it comes out to be quite different at 9.31, much like the advertised DF 9.2, so that is plausible as well.

Thus it will be worth while to get a softer clay and remold the piston for measurement, 0.3 is much too large a margin of error to work with. But right now i believe the number is 9.0.

So starting with 9.0, as increasing it by machining, here are the options:
Reducing the gap by 35mil yields a 25470ml³ volume for a 10.0 CR
20mil -> 9.5
50mil -> 10.5

Given confirmation on the temp, and piston dome, I will resist the urge to go straight to 10.5, 10.0 might be a more reasonable starting point...

I should note, reducing the cylinder head depth is not the only option, the cylinder itself can be reduced as there is a 2mm piston to deck height gap. Though popularhotrodding showed no power decrease for deck heights up to .125mil deep. so either or...

But despite what you may hear around these parts, going from 9.0 to 10.5 will only yield a theoretical 4.5% power increase:
http://www.popularhotrodding.com/tec...on_ratio_tech/

Unfortunately~60mph + 4.5% does not = ~80mph, not in our 3rd dimension anyway

btw, apparently these loncin engines came with a cylinder wall cross hatch hone
https://drive.google.com/file/d/0B-M...it?usp=sharing

I didnt expect that really...
I only mention this cuz a replacement cylinder wont have it.
Its just nice to know at least the loncin factory is doing some things better than others...
which just might carry over into other areas, who knows.

roadkill austn Is a lot of highways so im almost always on highway , when off highway indeed im in lower gears , never even touch 5th unless going over 60 mph , and hills cause me to down shift to hold 55-60

and It really dont matter how much deck u remove or turbo u add or nitrus u shoot , if u dont change gearing ,youll just pull to what u did be4 then valve float limit yourself


all I did was reverse stock air filter , and gear very tall , tall as could fit , oh and add 112 main (hair to big) to stock carb , stock otherwise

if u only ride in town and are comfortable with your rig doing 60 don't change a thing , as it will kill me off the line and probably on hills

I am not saying my rig is for everyone , My ride position has my feet straight out about 10" below my butt and the headlight/speedo act as air diverters up to mid chest level on me (would be like adding a wind screen on yours to have less drag) , and Im 165 on a heavy day

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Originally Posted by DanDaMan

roadkill austn Is a lot of highways so im almost always on highway , when off highway indeed im in lower gears , never even touch 5th unless going over 60 mph , and hills cause me to down shift to hold 55-60

and It really dont matter how much deck u remove or turbo u add or nitrus u shoot , if u dont change gearing ,youll just pull to what u did be4 then valve float limit yourself


all I did was reverse stock air filter , and gear very tall , tall as could fit , oh and add 112 main (hair to big) to stock carb , stock otherwise

if u only ride in town and are comfortable with your rig doing 60 don't change a thing , as it will kill me off the line and probably on hills

I am not saying my rig is for everyone , My ride position has my feet straight out about 10" below my butt and the headlight/speedo act as air diverters up to mid chest level on me (would be like adding a wind screen on yours to have less drag) , and Im 165 on a heavy day

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Lived in Austin for about a year and loved it. I went to the first 3 ROT rallies. Would love to retire to Bandera where maybe a little taller gearing would work for me. There are lots of good roads in the hill country for sure. That's part of why I asked about the tall gearing and hills/city riding. I lived on the I35 corridor and that traffic sux 24/7 almost from Round Rock to San Antonio. Rode a early Valk for awhile and that's the best bike I've ever oned.

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Originally Posted by DanDaMan

roadkill austn Is a lot of highways so im almost always on highway , when off highway indeed im in lower gears , never even touch 5th unless going over 60 mph , and hills cause me to down shift to hold 55-60

and It really dont matter how much deck u remove or turbo u add or nitrus u shoot , if u dont change gearing ,youll just pull to what u did be4 then valve float limit yourself


all I did was reverse stock air filter , and gear very tall , tall as could fit , oh and add 112 main (hair to big) to stock carb , stock otherwise

if u only ride in town and are comfortable with your rig doing 60 don't change a thing , as it will kill me off the line and probably on hills

I am not saying my rig is for everyone , My ride position has my feet straight out about 10" below my butt and the headlight/speedo act as air diverters up to mid chest level on me (would be like adding a wind screen on yours to have less drag) , and Im 165 on a heavy day

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So by this logic just gear high enough and we can all be hitting 125...
so what you don't seem to realize is that u need to have enough power to over come resistances.
Even a rock can hit terminal velocity if u drop it off the roof...

Why don't you get your self a gps, or borrow one, post a vid of you cruising at 80, and shut everyone up...

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Originally Posted by axa

So by this logic just gear high enough and we can all be hitting 125...
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no no no ive already stated I geared for 80 but valve float around 75 (the greater the motor strain the easier to valve float) , with 5th havng near no pulling power at all , but will try get a vid of me cruising over 70

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Originally Posted by DanDaMan

no no no ive already stated I geared for 80 but valve float around 75 (the greater the motor strain the easier to valve float) , with 5th havng near no pulling power at all , but will try get a vid of me cruising over 70

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alrite... now we're down to 70, even i with higher gear ratio can get to 64 (indicated) on a decline... but that's entirely not the point...
you made the impression that you can cruise at these speeds, so ok, post that vid even just at @70. not on a decline, not with your skewed speedometer...
still then i fear we will be watching a half hour video it will take for you to reach it...

got sort of tired of the "dont seem to realize arguments" everyone on the internet has all sorts of opinions and ideas, so i thought i would demonstrate the theory about all this.

Total power required
P(total) = P(rolling resistance) + P(wind) + P(gravity) + P(acceleration)

First Pg, gravity is eliminated as we don't care about descending a hill as I mention even a rock can hit terminal velocity, and of course these speeds are not attainable climbing, so don't even try it...

Secondly Pa, acceleration also drops for its not really a question about how long it will take dan to reach these speeds, only that it can be reached....


So then we are left with:

1 Pr Rolling resistance.

The power required to overcome rolling resistance can be described by the formula P = Crr x N x v, where

P is the power required.
Crr is the rolling resistance coefficient. define this based on the type of bike (road, mtb, cross) you used.
N is the normal force of the bike and the driver against gravity.
v is the rider velocity

As exact factors don't matter as long as they are consistent, and frankly we don't know them, we use 1.

@60mph
Pr = 1 * 1 * 60
@80mph
PR = 80

Here we can see this measure is linear vs speed, so the power required for rolling resistance alone is 33% greater for dan than others. (80-60) / 60 = .333333


2 Pw Wind resistance

The power required to overcome wind resistance (drag) can be described by the formula P = 0.5 x ρ x v3 x Cd x A, where:

P is the power required.
ρ is the density of air.
v is the rider velocity, relative to the wind.
Cd is the drag coefficient.
A is the the surface area of the rider facing the wind.

again keeping this constant for unknown factors:

@60mph
Pw = .5 * 1 * 60³ * 1 * 1 =
½ 60³ = 108000

@80mph -> 256000

Here you can speed is the factor cubed, so dans power contribution requirement is 137% greater than others. (256000/108000) / 108000
wow

Conclusion:
Without knowing all of these other coefficients I can not plug in the numbers to get the real power dan claims his higher gearing has compensated for...

But I only suggest that at highways speeds, wind is the greatest resistance to be overcome, and he has at least enough power to overcome 137% MORE of it than i do...


great hope for the argument that there is still power to be had by lifting the float ceiling. but still, who wants accelerate at a snails pace...
that's why i believe the real discussion is not about how to reduced gear ratios, but how to increase power.

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Originally Posted by axa

great hope for the argument that there is still power to be had by lifting the float ceiling. but still, who wants accelerate at a snails pace...
that's why i believe the real discussion is not about how to reduced gear ratios, but how to increase power.

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man u seriously spamming bars thread , because I can . or claim, to be able to go 13-15 mph faster than u ?

as for power to money , best buy would be a turbo , to add nuther 2-4hp , as decking/compression ect prob add 1 or 2 for a lot more time and $$ , and those numbers might all be "to hopeful"

and the motor is nearly "square" allowing a lot more power thru out the powerband , which allows a bit more pull at lower rpms , so stretching gears made sence to me

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Originally Posted by DanDaMan

man u seriously spamming bars thread , because I can . or claim, to be able to go 13-15 mph faster than u ?

as for power to money , best buy would be a turbo , to add nuther 2-4hp , as decking/compression ect prob add 1 or 2 for a lot more time and $$ , and those numbers might all be "to hopeful"

and the motor is nearly "square" allowing a lot more power thru out the powerband , which allows a bit more pull at lower rpms , so stretching gears made sence to me

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you would be surprised who barnone thinks is spamming this thread....
get that vid yet? im expecting to see this when you hit 80 on that desert highway...

Quote:

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Originally Posted by DanDaMan

man u seriously spamming bars thread , because I can . or claim, to be able to go 13-15 mph faster than u ?

as for power to money , best buy would be a turbo , to add nuther 2-4hp , as decking/compression ect prob add 1 or 2 for a lot more time and $$ , and those numbers might all be "to hopeful"

and the motor is nearly "square" allowing a lot more power thru out the powerband , which allows a bit more pull at lower rpms , so stretching gears made sence to me

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I for sure am not a mech, but I've always believed that there is a pretty much standard powerband for all 4 stroke OHV engines that can be played with by cam grinds and carb tweaks. I thought it was somewhere in the 4.8 to 5.5K range. I just got around to installing a tach on my bike and now have numbers that go with my rider feel. She seems to have plenty of torque from roll on (idle is 1800) to about 5K. Anything much above that is more noise than anything else. I'm not a speed at any cost person so I've always ridden where she feels right. On my ride, regardless of gear, that seems to be in the 5 to 5.5K range. It would be good to hear from other riders with tachs to see what their "butt dyno" tells them about the powerband.

It is my understanding that gearing is only to keep the motor in it's powerband so, you can gear for work as in a tractor, or speed as in a car. My father drove 18 wheelers and I remember that it required up to 18 gears so stay in the narrow powerband of the early diesel motors. I'm thinking that torque gets you there, but horsepower keeps you there? Anyway, has anyone seen actual dyno runs on this motor to verify powerband?

Roadkill,
I have a tach on my DF and I am seeing about the same power band as you. I did hit 70 MPH indicated today on a long steep downhill run at 6700 plus RPM but that doesn't count. My normal top speed is about 60 MPH indicated. No GPS to check speedometer.
She does seem to run out of juice at 5500 or so RPM.

axa,
Also saw 425 F on my cylinder head temperature gauge on a long steep up hill climb wide open throttle in 4th gear.
I eased off on the throttle and the CHT went down nicely.

Anyway, I had a nice ride on the Dragon today. She is running just fine.

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Originally Posted by barnone

Roadkill,
I have a tach on my DF and I am seeing about the same power band as you. I did hit 70 MPH indicated today on a long steep downhill run at 6700 plus RPM but that doesn't count. My normal top speed is about 60 MPH indicated. No GPS to check speedometer.
She does seem to run out of juice at 5500 or so RPM.

axa,
Also saw 425 F on my cylinder head temperature gauge on a long steep up hill climb wide open throttle in 4th gear.
I eased off on the throttle and the CHT went down nicely.

Anyway, I had a nice ride on the Dragon today. She is running just fine.

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I've been looking for gps speedometers for a while now but can't justify cost on a $2,000 bike. If I could find a nice 2 1/2 inch unit with turn signal and neutral indicators, I would pull the stock speedo. I had a Trail Tech computer with the magnet pickup on another ride, but just didn't like it

I just need to buy or borrow a GPS to see what % error I have on my DF's speedometer and I will be happy.

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Originally Posted by barnone

I just need to buy or borrow a GPS to see what % error I have on my DF's speedometer and I will be happy.

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I measured the DF stock speedometer to be almost exactly 10% over.
I cant say for sure if it is linear, but the mechanics of it lead me to believe so.
That has proved accurate enough for me... an easy calculation to do in your head and get to keep your stock spedo.

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Originally Posted by axa

I measured the DF stock speedometer to be almost exactly 10% over.
I cant say for sure if it is linear, but the mechanics of it lead me to believe so.
That has proved accurate enough for me... an easy calculation to do in your head and get to keep your stock spedo.

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It's one of those cosmetic things, actually. 10% at 60 mph isn't that important to my daily riding style. The stock one isn't ugly but if can get a different look plus accuracy for not to much cash I'll do it. I only gave $17.00 for the tach new and mounted it on the choke side of the bars. I 'm looing for the speedo or an anolog oil pressure or temp guage to mount on the other side.

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Originally Posted by Roadkill

It's one of those cosmetic things, actually. 10% at 60 mph isn't that important to my daily riding style. The stock one isn't ugly but if can get a different look plus accuracy for not to much cash I'll do it. I only gave $17.00 for the tach new and mounted it on the choke side of the bars. I 'm looing for the speedo or an anolog oil pressure or temp guage to mount on the other side.

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how could one install an oil pressure gauge on an 167fmm without machine work?
i dont reckon you could, else barnone would have it already, wouldn't you barnone....
though that oil temp thingy he has is pretty cool, id like it in analog...

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Originally Posted by axa

how could one install an oil pressure gauge on an 167fmm without machine work?
i dont reckon you could, else barnone would have it already, wouldn't you barnone....
though that oil temp thingy he has is pretty cool, id like it in analog...

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That.s what I'm thinking also about the oil, but I keep looking for something that might work with a mod. For temp, I'm thinking a digital unit with the display mounted in a speedo type case might be nice. I just don't like the space ship look of most of the factory units. I had the Trail Tech computor that had lots of good info, but it was always in the wrong screen for what I wanted and it was also ugly! I've used several of the digital ones from China for less than 10 bucks in my work. Many of the big rigs have a pyrometer mounted on the stack also.

Just a quick heads-up to you DF owners,

I posted some time ago on changing out the stock coil for one of the orange "performance" coils from Amazon. As it turns out, the coil was the cause of my speedometer not working with the engine running unless I unplugged/reconnected it. It leads me to believe that either my coil was not grounding properly, or that the style of coil itself is not sufficient for use on our bikes. It took me taking a good month's break of messing with the bike and focus on my 280Z, only to come back and resolve the issue in about 15 minutes. Just want to save you guys some headache should you consider the coil swap, or have already swapped and have the same issue.

t

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Originally Posted by axa

how could one install an oil pressure gauge on an 167fmm without machine work?
i dont reckon you could, else barnone would have it already, wouldn't you barnone....
though that oil temp thingy he has is pretty cool, id like it in analog...

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The oil temp thingy that I have is not an oil temp thingy but a cylinder head temperature thingy. Never felt the need for an oil pressure gauge.

I just ordered this http://www.aliexpress.com/item/CG125...974573329.html but in a black radiator. Perhaps an oil temp and/or pressure could be incorporated with it?

That oil cooler is interesting. I hope it proves effective.
How do you know that a CG accessory might fit this clone?

Snap a few pics of the head and i/o ports before install, if you don't mind, Id be curious if i could clone one myself...

Any ever change there starter?

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Originally Posted by Tedub

Any ever change there starter?

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Yes I have.I bought one and it worked fine, but I actually did not need to replace it.Why?

My bike stopped starting and the starter whines but doesn't seem to engage the engine. It will push start. Any ideas. I just replaced the battery and that didn't work.

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Originally Posted by Tedub

My bike stopped starting and the starter whines but doesn't seem to engage the engine. It will push start. Any ideas. I just replaced the battery and that didn't work.

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Buy bowtiewagon's old starter and try it.

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Originally Posted by Tedub

My bike stopped starting and the starter whines but doesn't seem to engage the engine. It will push start. Any ideas. I just replaced the battery and that didn't work.

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Tedud,I recommend you go back to page 504 of this thread and read through(basically filtering through with most of my posts.) Pay attention to post #5068.There will be links attatched to that post of the part in question You will see pictures i took of my issue and then a few posts on how to fix the problem. If you have any difficulty with this please feel free to send me a pm , but you must set your pm to recieve replies,I tried to pm you back and you do not accept any pm's.

Also, one thing.When reassembling..DO NOT TORQUE DOWN ON THE CRANK SHAFT BOLT. The shaft has a key on it, so everything just needs to be tightened down hard.

suggested tool to use include
large rubber strap type oil filter wrench
RENT a puller (large) from autozone
RENT an impact wrench from auto zone (just for removal of crankshaft bolt-righty tighty left loosy)
8mm socket-removes covers

be sure to pay attention to the clutch assembly when removing it, there is an arrow on the back side of it, for rotation of the clutch,it needs to be put back on that same way. When i recieved my new starter clutch assembly,I had to take the race out of the center and turn it around so that the arrow was on the back and the flow was correct..you may need to do the same thing..but not sure.

it is not hard to do.
You take the cover off, remover all the gears that lead to the starter, use the impact gun to remover the bolt on the crank shaft, use the puller to remove the drum from the shaft, after you unbolt the three bolts in the center of the drum, then the clutch comes off, -reverse procedure to assemble.

check your oil for metal shavings..I hope you have a magnetic drain plug..I think my plug saved the bike..drain the oil, run..drain the oil, run drain the oil..should be good to go. Hope this helps.

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Originally Posted by Tedub

My bike stopped starting and the starter whines but doesn't seem to engage the engine. It will push start. Any ideas. I just replaced the battery and that didn't work.

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Bad starter clutch.bowtiewagon just posted the info about it.

me too...

jfyi, page numbers are useless as one can rearrange the order as i do... this is page 1 for me... i like to see the newest posts on the top of the page...

each post number has a link that can be made hyper

Gotcha, here is the page I was talking about.
http://www.mychinamoto.com/forums/sh...mation/page507

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Originally Posted by bowtiewagon

Gotcha, here is the page I was talking about.
http://www.mychinamoto.com/forums/sh...mation/page507

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there you go with the page again... :rolleyes1: , you see when i, or others might, hit that link, they get page 507, which depending on how you set up your preferences can be an entirely different page... what you want to do is right click the # of the post and get its link...
anyway, just trying to help out.. dont mean to be a douche or get off subject.:mwink: