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#5071 Re: Dong Fang DF 250 RTB Bobber Information
- Join Date
- Dec 2013
- Location
- TX
- Posts
- 92
06-23-2014, 12:08 PMThanks 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.
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#5072 Re: Dong Fang DF 250 RTB Bobber Information06-23-2014, 12:44 PM
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 ) System Engineer.
If you google 167fmm or CG125 you can find lots of info on the DF engine. These are nice simple bikes.
0522141526-00.jpg
Off to the dump/recycling center with another load.Vince
2021 Ural cT
2022 Dong Fang DF250RTG
2021 Ice Bear 150cc scooter
2020 Ice Bear 150cc Scooter
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#5073 Re: Dong Fang DF 250 RTB Bobber Information
- Join Date
- Dec 2013
- Location
- TX
- Posts
- 92
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#5074 Re: Dong Fang DF 250 RTB Bobber Information06-23-2014, 02:10 PM
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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#5075 Re: Dong Fang DF 250 RTB Bobber Information06-23-2014, 02:49 PM
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...
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#5076 Re: Dong Fang DF 250 RTB Bobber Information06-23-2014, 04:02 PM
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...2012 DF250RTB_B with Yamaha XV250 V-twin
1998 XVS650 (For Sale)
2003 LS650 with Voodoo Vintage hardtail
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#5077 Re: Dong Fang DF 250 RTB Bobber Information
- Join Date
- Aug 2011
- Location
- texas
- Posts
- 266
06-23-2014, 11:06 PMfinally 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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#5078 Re: Dong Fang DF 250 RTB Bobber Information06-24-2014, 03:42 PM
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...
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#5079 Re: Dong Fang DF 250 RTB Bobber Information
- Join Date
- Aug 2011
- Location
- texas
- Posts
- 266
06-24-2014, 07:08 PMI 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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#5080 Re: Dong Fang DF 250 RTB Bobber Information06-24-2014, 07:11 PM
DanDaMan,
Any engine mods?Vince
2021 Ural cT
2022 Dong Fang DF250RTG
2021 Ice Bear 150cc scooter
2020 Ice Bear 150cc Scooter
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