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  1. #1 Zongshen 167FMM and 169FMM crankshafts 
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    Has anyone attempted to put a Zongshen 167FMM crank and/or rod in a 169FMM motor which would technically stroke it closer to a 250cc?

    I believe the ZS167FMM is 67mm bore, 65 (or 66)mm stroke. The ZS169FMM is a 69mm bore, with only a 62.5mm stroke. Is it the rod length or crank that is different? Thoughts? The 167FMM rods and cranks are pretty cheap, even if it meant doing a bit of valve clearancing it might be fun to try.
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  2. #2 Re: Zongshen 167FMM and 169FMM crankshafts 
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    I was also wondering about the 171FMM cylinder head (71mm bore) with a 167FMM crank stroke (65mm).

    Anyone??
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  3. #3 Re: Zongshen 167FMM and 169FMM crankshafts 
    Senior C-Moto Guru axa's Avatar
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    Quote Originally Posted by Crackerjacc View Post
    I was also wondering about the 171FMM cylinder head (71mm bore) with a 167FMM crank stroke (65mm).

    Anyone??
    strictly speaking about the stroke, which is 65mm on a167FMM, when I decked my head I calculated a static CR from 9 to 10.5 with only a 50 mill shave. 2.5 mm would be more like 13 CR which doesn't seem realistic, but the real or dynamic CR is much more difficult to calculate. I wonder if it would be feasible considering that.

    what I don't think would have worked is valve clearance with another 1 to 2 mm, I'd estimated the poison needs a bit of machining.

    the 167 had at least 3mm of wall to support the rings but don't know about others.

    fwiw the power gain due to compression is hardly worth it, wonder if the diameter increase is worth it.

    here's the calculations​ for what that's worth:

    3525.65236
    Bowl 22cc = 22000ml≥
    TDC to deck 2mm = 7051ml≥
    Gasket 1mm = 3526ml≥
    Piston dome 4/5cc = -4000ml≥
    Stroke 65mm = 229167.404
    229167:22000+7051+3526-4000
    246589:22000+7587+3794-4000
    (229167.404+28577)/28577
    9.02<>8.96

    3107.55614 -> 25470 = 10.0 -> 35mil
    20mil -> 9.5
    50mil -> 10.5

    229167:20000+7051+3526-4000
    26577
    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: Zongshen 167FMM and 169FMM crankshafts 
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    wow, very cool that you explored it out. From reading your calculations it probably wouldn't be worth the effort or money to stroke the ZS169 and would require a custom piston I'm sure. Interesting why Zongshen went with to different setups though? 67mmx65mm VS 69mmx62.5mm to achieve similar displacement.

    I was just hoping a rod change and perhaps minimal piston modding would be feasible.

    It's too bad the JIANSHE 400cc ATV cylinder head is slightly different. The design is almost identical but with 83mm bore.



    Quote Originally Posted by axa View Post
    strictly speaking about the stroke, which is 65mm on a167FMM, when I decked my head I calculated a static CR from 9 to 10.5 with only a 50 mill shave. 2.5 mm would be more like 13 CR which doesn't seem realistic, but the real or dynamic CR is much more difficult to calculate. I wonder if it would be feasible considering that.

    what I don't think would have worked is valve clearance with another 1 to 2 mm, I'd estimated the poison needs a bit of machining.

    the 167 had at least 3mm of wall to support the rings but don't know about others.

    fwiw the power gain due to compression is hardly worth it, wonder if the diameter increase is worth it.

    here's the calculations​ for what that's worth:

    3525.65236
    Bowl 22cc = 22000ml≥
    TDC to deck 2mm = 7051ml≥
    Gasket 1mm = 3526ml≥
    Piston dome 4/5cc = -4000ml≥
    Stroke 65mm = 229167.404
    229167:22000+7051+3526-4000
    246589:22000+7587+3794-4000
    (229167.404+28577)/28577
    9.02<>8.96

    3107.55614 -> 25470 = 10.0 -> 35mil
    20mil -> 9.5
    50mil -> 10.5

    229167:20000+7051+3526-4000
    26577
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  5. #5 Re: Zongshen 167FMM and 169FMM crankshafts 
    Senior C-Moto Guru axa's Avatar
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    as i and many before us have found , significant power gain is usually achieved with a different bike entirely.
    I just don't see how one could get the parts and spend the time experimenting to see what fits and what works on these poorly documented engines.
    good luck
    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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