How to measure your cylinder bore (pics)

Discussion in 'Engine' started by JPMartin86, Jun 9, 2009.

  1. JPMartin86

    JPMartin86 New Member

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    What you'll need:
    Cylinder
    Bore Gauge
    Digital Micrometer
    Pen
    Paper
    Calculator

    CIMG5157.jpg

    You'll use the bore gauge to find the width of the cylinder as shown in the picture. Make sure the bore gauge is level then tighten the lock.

    CIMG5159.jpg


    You will measure 3 spots; Top being (x), Middle being (y), & Bottom being (z) of the cylinder. Each spot will be measured in 3 different angles. Each color represents a different angle
    Red being (1), Blue being (2), Yellow being (3).

    crisscross.jpg

    After you have tightened the bore gauge use the digital micrometer to measure the bore gauge. Its good practice to zero out the micrometer before measuring. Make sure to write down each measurement.

    CIMG5160.jpg

    For example my measurements are:

    X1 - 66.39mm
    X2 - 66.45mm
    X3 - 66.46mm

    Y1 - 66.38mm
    Y2 - 66.48mm
    Y3 - 66.43mm

    Z1 - 66.47mm
    Z2 - 66.42mm
    Z3 - 66.46mm


    The reason you have measured the bore in 3 spots at 3 different angles is (a) to get the average bore size and (b) to find the cylinder taper. The math to find your average bore size of each "spot" is:

    X1+X2+X3= 199.3 ÷ 3 (the # of times you measured the "spot") = 66.43mm

    66.43mm will be my average for the (x) measurements.

    You can then do the math of each "spot" average to get an overall bore size.

    (x average) + (y average) + (z average) = 199.31 ÷ 3 = 66.44mm



    The Blasters stock bore is 66mm. As you can see my cylinder is worn out pretty good, and i will need to have it bored out to 66.5mm. Here is a chart to figure out what your next bore size will be and what piston/rings to purchase.

    66.0mm - .000 bored over
    66.5mm - .020 bored over
    67.0mm - .040 bored over
    67.5mm - .060 bored over


    I am not a professional engine builder or a master mechanic so if there is any wrong information here please let me know and i will correct it immediately.
     
    Last edited by a moderator: Feb 17, 2014
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  2. blasterboy069

    blasterboy069 New Member

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    I would like to rebore my engine to a wiseco over .060. how do you rebore it ? do you have to polish it after or ?
     
  3. Cochise

    Cochise New Member

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    Very helpful post!
     
  4. NOVIS

    NOVIS New Member

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    very helpful. i remember doing this in auto clas lol. +1
     
  5. samolia

    samolia Member

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    only one problem with the post thats not a micrometer that a digital vernier caliper..

    a micrometer looks like a C-clamp and are much better for what your doing..IMO [​IMG]

    other then that good job!!
     
  6. JPMartin86

    JPMartin86 New Member

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    Thank you for the correction.
     
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  7. JPMartin86

    JPMartin86 New Member

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    You probably cant do it yourself. You would need a cylinder boring machine like this one.

    [​IMG]

    After its bored you do not polish it, you will need to hone the cylinder to a "cross hatch" as seen in this pic.

    [​IMG]
     
  8. mpiller

    mpiller New Member

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    Where did you get the bore gauge?
     
  9. yamahablaster19

    yamahablaster19 New Member

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    Very helpful post thanks
     
  10. jus_me

    jus_me Active Member

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    nice post.. have some green..
     
  11. barttskyus

    barttskyus New Member

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  12. AssWild

    AssWild New Member

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    Im putting a .020 over kit in my blaster and machine shop asked me what piston or rings clearan es are are pls help
     
  13. mustangdave

    mustangdave New Member

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    I was actually wondering the same, im sure i could just look it up but if someone more experienced would help... that would be much appreciated
     
  14. Blaaster

    Blaaster Moderator Staff Member Technician Forum Supporter

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    Give the shop the piston, and if they are any good they will know what tolerances to bore to.

    If they do not know, take it to a shop that knows what they are doing.
     

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