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  1. #1 looking for people interested in top end performance modifications 
    Senior C-Moto Guru axa's Avatar
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    I'm looking for any one in the NY/NJ/CT area that either needs a new top end on their 167fmm or wants to push performance by decking their cylinder head.

    I've done this to my top end rebuild with very good results going from the stock 9:1CR to 10:1, so I'd like to see find others who might want to try or take it even further.

    I'd like for them to be in my area so I can work on the bike in person, this isn't some prepackaged upgrade I'm looking to sell...
    we hang out here and talk about this stuff here sometimes:

    http://www.mychinamoto.com/forums/showthread.php?t=2738
    Dong Fang DF 250 RTB Bobber Information
    2012 DF250RTB_B; ported cylinder head decked at 10:1CR
    13/30 Sprockets
    Back cut valves, intake: .004, exhaust: .006
    jets = pilot: 45 , main: 115, needle: stock
    Intake pTrap air ram; Exhaust = stock No catalyst
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  2. #2 Re: looking for people interested in top end performance modifications 
    Senior C-Moto Guru Zorge's Avatar
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    You did just head decking, or something more (porting, removing "flange" around valve seats, etc.)?
    Ask me nothing - I DO NOT speak english. Really...
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  3. #3  
    Senior C-Moto Guru axa's Avatar
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    on my rebuild I did everything I could think of
    - decked head
    - port matching (widening openings to match connecting parts)
    - flange removal on any sharp angle (especially behind the valve seats)
    - rough surface polishing
    - back cut valves (taking off the sharp top ridge)
    - steel rods
    - cylinder cross hatch
    - lapping valves

    from there the jets get bumped up.

    I really wish I could get my hands on one of the wiseco 67.5mm oversized pistons and add a big bore to my repertoire...
    Last edited by axa; 04-25-2015 at 07:45 AM.
    2012 DF250RTB_B; ported cylinder head decked at 10:1CR
    13/30 Sprockets
    Back cut valves, intake: .004, exhaust: .006
    jets = pilot: 45 , main: 115, needle: stock
    Intake pTrap air ram; Exhaust = stock No catalyst
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  4. #4 Re: looking for people interested in top end performance modifications 
    Senior C-Moto Guru Zorge's Avatar
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    And?

    Can you make comparsion between "before" and "after"?
    Ask me nothing - I DO NOT speak english. Really...
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  5. #5  
    Senior C-Moto Guru axa's Avatar
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    I've now had several hundred miles and can make some specific comparisons.

    one main point is on long gradual inclines I am now able to hold momentum with traffic. where before I could not and would gradually slow down to a certain point.

    this made me confident to try a 13/30 sprocket combination that I am now pleased with.

    right now I am unsure of the top speed as I've only recently changed the gearing and because I'm having some engine surge problems at full throttle. but in the next few weeks I should know for sure.
    before on flat road I could perhaps reach about 55mph max with 13/35 sprockets, now I've already reached about 65..

    unfortunately it is difficult to quantize the power increase, but it is noticeable and I feel it's significant to such a low power engine.
    only a dyno would tell the exact story. that's why I want to find others who will try.
    2012 DF250RTB_B; ported cylinder head decked at 10:1CR
    13/30 Sprockets
    Back cut valves, intake: .004, exhaust: .006
    jets = pilot: 45 , main: 115, needle: stock
    Intake pTrap air ram; Exhaust = stock No catalyst
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  6. #6 Re: looking for people interested in top end performance modifications 
    Senior C-Moto Guru Zorge's Avatar
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    Not once I had a chance to read the experiences of people who have done, so to say, "valve job" (just playing around valve seats was sufficient) on the small displacement horizontal cylinder engines.

    They say that after such intervention on the engine, the zone where the intensive vibrations are starting, shifted upward by a 1000 or 1500 rpm.

    Did you feel something like that on your engine?
    Ask me nothing - I DO NOT speak english. Really...
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  7. #7  
    Senior C-Moto Guru axa's Avatar
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    I'm not sure if what I did qualifies as classic valve job but often I consider that all these small things including valve lapping and back cut helped add up to the final result.

    before the engine work I had the same cheap Chinese tachometer, I'm not sure if something about it changed, but now my top end reads about 500 rpm or more higher than it did before..
    with filter attached I could achieve about 7k, now I can reach near 8 and as I mention I have top end surge problem so I don't push it to it's limit yet.
    this is also hard to quantize because I don't trust that cheap tachometer at all. but it is reasonable to suspect all these small changes lead to the higher top engine speed.

    Also I feel I need to idle at a higher rpm else it tends to stall.
    as well it being a bit more difficult to stay when cold.
    these I suspect possibly due to the higher engine compression, but I can't be sure.

    but I do not notice any difference in engine vibration. for one thing before the engine work I removed the top end engine mount bracket. I first worried any extra vibration helped caused my valve to break which destroyed the engine. so when I rebuilt it I replaced that bracket. there's no good reason to remove it and risk added vibration.
    2012 DF250RTB_B; ported cylinder head decked at 10:1CR
    13/30 Sprockets
    Back cut valves, intake: .004, exhaust: .006
    jets = pilot: 45 , main: 115, needle: stock
    Intake pTrap air ram; Exhaust = stock No catalyst
    Reply With Quote  
     

  8. #8 Re: looking for people interested in top end performance modifications 
    Senior C-Moto Guru Zorge's Avatar
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    What I mentioned earlier was a basic removal of a flange... how to say... in front of the valve seats, just around valve heads. On stock head (at least, on those horizontals), valve heads are preety "drowned" in motor head and when they start to open, in first few milimeters air flow is very reduced. Allegedly, by removing this "flange", air flow improves so engine pumps bit more power (this I understand), and, as I mentioned - vibrations are starting on higher revs (???).

    BTW, did you do something with valve springs, try stiffer ones or something else?




    Damn, my English is killing me!
    Ask me nothing - I DO NOT speak english. Really...
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  9. #9  
    Senior C-Moto Guru axa's Avatar
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    I understand your what you want to say.
    I tried to remove any ridge (flange) that I found. when the valve seats are inserted in the head they don't perfectly match the contour of the port, therefore a ridge is made. I did my best to remove those.

    but remember here we are talking about a very low power engine so the theoretical gain is not that much anyway .

    I did not try any special valve springs. I used the new valve springs that came with the new head.
    actually I was very disappointed with the new springs as they arrived rusted, they did not seem to me quality material.
    but they were stiffer than the old ones and as far as I know, my valve failure could have been caused by the old valve springs so I used the new springs.
    so far so good.
    Last edited by axa; 04-26-2015 at 07:02 AM.
    2012 DF250RTB_B; ported cylinder head decked at 10:1CR
    13/30 Sprockets
    Back cut valves, intake: .004, exhaust: .006
    jets = pilot: 45 , main: 115, needle: stock
    Intake pTrap air ram; Exhaust = stock No catalyst
    Reply With Quote  
     

  10. #10 Re: looking for people interested in top end performance modifications 
    Senior C-Moto Guru Zorge's Avatar
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    Quote Originally Posted by axa View Post
    but remember here we are talking about a very small power engine so the theoretical gain is not so much anyway
    O, I stop believing in Santa Claus long time ago.

    Say, what you use for smoothing rough surfaces inside ports? I saw guy who, after cutter job, used piece of "Mirka's" abrasive mesh, cutted to form some kind of flaps, fixed on a splitted stud on a common drill or dremel. I was surprised when i saw results. Plus, IMO at least, this way is practically "idiot-proof" and the chances for something to go wrong are significantly reduced, which is great for us, weekend mechanics.
    Ask me nothing - I DO NOT speak english. Really...
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