38 or 40mm?

Discussion in 'Norm's 2 stroke repair center' started by Wags, Sep 17, 2016.

  1. Wags

    Wags New Member

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    I have a zl rod in my engine and when I took it apart for the first time I found that It has the piston with the lower wrist pin hole. From what I understand that would make the rod a 38mm. Fred from cr machine (Fred head) states in his video that the zl rod is a 40mm stroke. I feel like he knows what he is talking about but as far as I know the piston would hit the head with the lower holed piston if it is a 40mm. Does anyone know if the zl rod is a 38 or a 40mm ?
     
  2. Tyler6357

    Tyler6357 Member

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    40mm is not the connecting rod length, it's the piston stroke
     
  3. Wags

    Wags New Member

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    Maybe I'm wrong but I thought the piston was connected to the rod. From big end bearing to wristpin end of rod measurement should be either 90 95 depending on rod, and a few in between. The crank from what I understand is what provides the stroke. I'm asking if the zl rod belongs in the 38 or the 40mm stroke family? There are many different combinations to get the tranfers to open when you want so my question Is a general rule of thumb question.
     
  4. dob1385

    dob1385 New Member

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    Im using the zl rod with the middle wrist pin. It was advertised as 40mm stroke but I havent actually measured. From what I understand (and i might be wrong) the zl rod can work with either piston to get 40mm depending on the cylinder.
     
  5. Wags

    Wags New Member

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    It turns after some extensive research, most of the vendors would have you believe that there are two different piston, but this isn't the case. There are 4 or 5 piston variations and you put that with 5 or 6 different conecting rods with a couple different cylinders, that makes a rather large number of combinations. What I found out is it's all about clearances at TDC and BDC. each configuration will change something like timing or stroke. There doesn't seem to be very many standards which is why most refer to 3 main engine types, the gt5, the pk80 and the half-breed. I am still somewhat new at this so I could be all wrong but this seems to be what I found in the last week after hours of reading and conversations. So in conclution it does not surprise me that you are using the piston with the wrist pin in the middle and im able to use the piston with the hole twards the bottom on the same ZL style rod.
     
  6. broke and hungry

    broke and hungry New Member

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  7. Wags

    Wags New Member

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    Yes, crazy. I do like all the different options now that I kind of understand. We can't bore these things for a reasonable price and you have to find the horse power somwhere. It would seem each platform offers something a little different to build off. Imo
     
  8. Greg58

    Greg58 Well-Known Member

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    To find the stroke of your engine is fairly easy, with the head removed measure the distance from the top of the cylinder to the piston at bottom dead center. This is the stroke that the piston travels, numbers or letters on rods are probably coding by manufacturers.
     

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