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?