So How Do You Measure to Find Out The Stroke Of An Engine?

Discussion in 'Engine Topic' started by Bandit723, Feb 20, 2017.

  1. Bandit723

    Bandit723 Veteran Member

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    Read many articles on this and is still confusing as fudge. articles will do the calc thing but never tells where the stroke is measured from. From the top of the piston as it travels down?
     
  2. CasperCasper

    CasperCasper Veteran Member

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    You could do that. If you do use a mounted dial indicator to find the appropriate tdc and bdc. Most guys problably use google and the casting number on their crank
     
  3. Bandit723

    Bandit723 Veteran Member

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    well seems google does not do much when using a non stock crank and a non stock piston rod in a engine block that they were nominally not built in.
     
  4. CasperCasper

    CasperCasper Veteran Member

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    Then use a dial indicator to find tdc and zero it, then go to bdc as indicated by the max value on the dial indicator and youve got your stroke ;) Do it in three different spots to ensure your dial indicator is square. All three should converge to a value. Thats how id do it.
     
  5. CasperCasper

    CasperCasper Veteran Member

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    Btw rod length doesnt affect stroke. It is a function of your crank. What kind of crank do you have?
     
  6. Bandit723

    Bandit723 Veteran Member

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    it's a 350 crank, don't have the part number "lost it"
     
  7. Bandit723

    Bandit723 Veteran Member

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    so if i am reading into this right the 350 crank gives me a 3.484 inch stroke and the 400 block 30 over is a 406 less the fuzzy math bringing it out to 377 cubic inches?
     
    Last edited: Feb 21, 2017
  8. CasperCasper

    CasperCasper Veteran Member

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    Yup. I tried a calc and got the same.
     
  9. Bandit723

    Bandit723 Veteran Member

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    Thanks...
     
  10. Hey G

    Hey G Veteran Member

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    I am not an engine builder, but I am a machinist. To get the most accurate reading, it would be best to do this on a flat surface with some special tools like a height gauge and micrometer. If you set the crank so one rod journal is straight up, then you could measure. First, I would find the distance from the top of the rod journal to the top of the main journal using the height gauge. Let's say 1.575" was your reading, for this example. Then measure your rod and main journals with a micrometer. Then subtract half the rod journal (2.10" standard, for this example), 1.575" minus 1.05" giving you .525". Then add half of the main journal (2.45" standard, for this example), .525" plus 1.225" giving you 1.75". That number is the distance from the center of the main to the center of the rod... and that equals half your stroke. Then multiply by 2...3.5" for this example only. Hope this helps.

    G
     

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