Bore size

Discussion in 'Gas Engines' started by Danielsan, Apr 16, 2020.

  1. rxcomposite
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    rxcomposite Senior Member

    It seems you conversion is wrong. 0.001" = .0254 mm, thus .005"= 0.127 mm.
    Thus if the standard bore is 98.425 mm, +98.552 mm (+0.005"), -98.299 mm (-0.005") it should be fine.

    Like I said, for a quick check, try to fit the rings and see if the gaps are within specs. If there is a gap, it means your measuring instrument is fine and everything should fit as planned. If the gap is larger than spec'ed, then worry. Something is wrong.

    For small block engine, it is usually rated as (in Imperial) Standard or Zero, +1 (+0.010"), +2(+0.02"), +3(+0.030), +4(+0.040"). If it is within +-0.005" or 5 mils (+-0.127 mm), then it is within tolerance and still usable. Anything above standard is an overbore.
     
    Last edited: Apr 19, 2020
  2. BlueBell
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    BlueBell . . . . .

    From Danielsan, post #6:
    "I also measure the gap of the segment rings: 0.40-0.45mm that seems correct."
     
  3. Danielsan
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    Danielsan Amateur designer-builder?

    Its new i set it to 99mm with a micro meter and put the dial 0
     
  4. Danielsan
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    Danielsan Amateur designer-builder?

    Hi RX,
    unless I got mistaken or some printed specs are not ok I read ±0,0005" which is 0.0127... that corresponds to the red and green line on my graph...

    I ordered a 100mm caliber for my micrometer and check again...
     
  5. rxcomposite
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    rxcomposite Senior Member

    So which one is it, 0.001" (1 mil) or 0.0005" (1/2 mil)?
     
    Last edited: Apr 20, 2020
  6. Danielsan
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    Danielsan Amateur designer-builder?

    haha gets confusing these imperial dimensions 0.0005" 3x 0 not 4x 0
     
  7. rxcomposite
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    rxcomposite Senior Member

    It gets confusing at times if you did not grow up with it. It is like a language.

    I grew up using the English system with all of my books coming from the US but during college days, our government ordered us to use metric. That makes me "bi lingual" but is a disadvantage in the modern world.

    In this case, it makes more sense. Talking in mils (0.001"), +1=0.01" (10 mils), +2, ect. A mil is what you can accurately measure or machine. Less than that and it takes a "ladies touch" with the measuring instrument or skill in using the machine. I struggle with half a mil tolerance.

    But if you are used to Metric, there is no need to use English. Just follow what the manual says and use only equipment with metric divisions.
     
  8. DCockey
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    DCockey Senior Member

    There is also the difference in whether to include the zero before the decimal indicator. 0.001 vs .001 vs 0.01 I've seen this cause confusion and errors when someone only looks at the number of zeros and not the location of the decimal indicator.

    The term "mil" refers to 1/1000 of something. So a millimeter is 1/1000 of a meter and a millinch is 1/100 of an inch. An common term in the US for 1/1000 of an inch is "thou" or "thousandth" (typical pronounced "thousands") as in one thousandth. Someone might say the clearance should be "three thou" or "three thousands".

    I'm also bilingual living in the US but worked in the auto industry which is almost entirely metric. I can work in either but it can be confusing going back and forth. Also interesting visiting Canada which is nominally entirely metric but still uses a lot of Imperial/English, particularly for lumber, plywood, etc.
     
  9. rxcomposite
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    rxcomposite Senior Member

    I will have to disagree a little bit with the terminology. I came to know "mil" before "micron". "Mil - A unit of measurement in the English system that is measured in thousandths of an inch. Micron - A unit of measurement in the metric system that is equal to one thousandth of a millimeter. The M-Shop uses only the English Imperial/US system (inches, feet, etc.)."

    mils to micron - Google Search https://www.google.com/search?rlz=1C1CHBF_enPH890PH890&sxsrf=ALeKk02nEoY86XT6jy27jQfqyD6DUHAhpQ%3A1587497428626&lei=1EmfXsfbJZWGoASC14GoDg&q=mils%20to%20micron&ved=2ahUKEwjP7oDjoProAhWSGqYKHaR7BcUQsKwBKAN6BAgEEAQ&biw=1536&bih=754
     
  10. DCockey
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    DCockey Senior Member

    I didn't mention "micron" or "one thousndth of a millimeter". I said "a millimeter is 1/1000 of a meter". A micron is one millionth of a meter.

    What is "M-Shop"?

    Added: To expand on use of "mil" a milliamp is 1/1000 of an amp, etc.
     
  11. rxcomposite
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    rxcomposite Senior Member

    Sorry DC I posted a confusion. You are technically correct in all aspects. It is just when we say it is a thousandth of a something, it will mean different in the metric system hence the use of terminology micro. Somewhere in this BD forum, there was a confusion in the use of mil and micron.

    M shop probably means "Machine Shop" but I am only guessing in the author's use. Drafting office is usually near the machine shop as it is meant to bridge the gap between the engineers and the machine shop.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    I'm still trying to understand why he has taken the head off this antique, if it was running OK, just say a few " hail Marys" and it is bound to keep going till it stops. I don't think too many old carburetted boat engines get rebuilt these days. Too fuel hungry.
     
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  13. sdowney717
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    sdowney717 Senior Member

    The stuck oil rings, well you need all new rings anyway, rings loose their spring tension. You can get the old oil rings off that piston, soak piston in ATF, that is a very good solvent- rust remover. Heat the piston first in the oven to 250 degrees F then soak in the ATF, cycle repeat.
    ATF seriously works. And even better mix ATF with Acetone.
    Do not score the piston ring lands (sides)
    Your cylinder bores sound just fine to me.
     
    DogCavalry likes this.
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