Info on stroking

Discussion in 'Advanced Technology & Engineering' started by MikeS, Sep 26, 2002.

  1. motometal

    motometal Lifetime Sponsor

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    if an engine with a given stroke gets the rod replaced with a longer one, and the piston dwells at tdc and bdc longer, isn't it logical that when the piston does start moving towards the other end of the stroke it would accelerate faster? It has less time to travel the same distance, gotta make it up somehow!


  2. MikeS

    MikeS Lifetime Sponsor

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    Hey wfo

    Getting back to the specific info on the RM85. I have my cases setting in front of me. There is atleast 3 mm ++ of room between the Rod big end and the cases so adding 3.2 mm stroke it will move the rod 1.6 mm closer to the cases. No Problem as you still have 1.4 mm plus . The crank itself is about .060" from the case. I am curious as to what some of these guys use epoxy for in the crankcase as there is not much room as it is.

    This thread has atleast given some good information plus raised more questions....Piston speed, ring design, Exhaust waves, Rod length, Crank balancing etc....

    Eric maybe you should write another book for the advanced subjects :p
  3. Jon K.

    Jon K. Subscriber

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    Ahh!! 3mm clearance. There you go! Thanks Mike.
  4. EricGorr

    EricGorr Super Power AssClown

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    motometal

    Yes you're right. Two things are happening when a longer rod and increased stroke are added to an engine. The piston dwells at TDC longer and enables the combustion pressure to increase before the piston accelerates down the bore with the added leverage affect. At BDC the rod spends less time so it can cause the reeds to open further and change the timing and duration of the intake phase.

    Sometimes these things make a big difference, sometimes they fight each other because it throws something else out of sequence. The point in my article is that stroking or boring doesn't always produce more power. Some engines like KX85,100 benefit from stroking but not boring. Some engines like the KTM65 lose with either mod. It just takes trial and error testing to determine what works best for what rider in a given soil type and terrain obstacle.

    The "What's All This Fuss" title sort of pokes fun at the tuners who are trying to rev up the consumers with exaggerated claims of what stroking can accomplish, other than fill their pockets with more cash.
  5. cr-man

    cr-man Lifetime Sponsor

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    I called and talked to crank works on the balance of stock cranks to find out where the manufacturer's stood on their balance and they told me Honda is the worst Yamaha and Suzuki are middle of the road and Kawasaki is the best as far as balance from the factory! I thought this was pretty interesting and thought I would share this info.
  6. marcusgunby

    marcusgunby Lifetime Sponsor

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    Ive often wondered if the vibes when riding the alloy frames on the honda could be made better with rebalancing the cranks.
  7. cr-man

    cr-man Lifetime Sponsor

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    I sent my crank out to crank works for balancing Marcus when I find out I'll let you know if it can help?
  8. motometal

    motometal Lifetime Sponsor

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    i'm a little foggy on the details of balancing, but I believe it's only possible to balance the engine for a certain range of rpm. In other words, in the case of my Honda, it's apparently balanced around the powerband, and not-so-balanced at low rpms. From my experience, Hondas and Kawasakis have the most vibration on their 250s.

    I have to chuckle a bit at the piston ads I have seen bragging "lighter weight than stock"...wait a minute...wouldn't you have to re-balance the engine?? :|
  9. marcusgunby

    marcusgunby Lifetime Sponsor

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    CR man i would like to hear how it works:)
  10. hot125mod

    hot125mod Rookie DRN Member

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    hey eric i have a mini dad friend that swears by putting a 52mm piston in his sons 05 kx 85 making it a 103 I think correct me if I am wrong. Now he got an idea to put a 54 mm piston in it. The water jacket must be so thin it seems like he fried it about every weekend and he had the pwr radiator on it too. Part of it is that he is a dumbass and ignores the fact that warming up his bikes before his kids ride is something that shouldn't be left out they locked a motor up faster than you can say "Wow that guy needs to not spend so much time drinking and pay attention to his bikes". Can't wait to hear from you. Thanks again. We all appreciate your wisdom and many things you have done for our sport. Keep on doin what you do best. YOU THE MAN ERIC. :)
  11. hot125mod

    hot125mod Rookie DRN Member

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    what do you think Eric? :nod:
  12. hot125mod

    hot125mod Rookie DRN Member

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    this is from a while ago but i want to know others opinions.
  13. hot125mod

    hot125mod Rookie DRN Member

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    could you get the same peak power from a good 125 mod as you could a big bore 134 or 139 or is it not possible. cant seem to remember but a 134 and 144 make the same peak power the 144 is just a lot more broad
    Last edited: Mar 5, 2008
  14. hot125mod

    hot125mod Rookie DRN Member

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    Is there any off the shelf pipe you could use for a stroker motor or long rod or not because these 2 change the timing too much?



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