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Thread: How do you mesure base circle?

  1. #1
    Senior Member DYNO OPERATOR
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    How do you mesure base circle?

    How do you the mesure base circle on a cam? ops:
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  2. #2
    Senior Member RACING JUNKIE
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    A little tricky.
    1. You must have a known standard cam. Rotate it to the heel position and using a lifter and dial indicator -measure your inital base number. Slide the lifter out while leaving the dial in place.
    2. Install suspect cam at the heel position. Install lifter under the dial indicator and check the difference.

    For SBC's the usual standard base circles are .950, .900 or .875. A custom cam may have any possible number.
    O

  3. #3
    Senior Member RACING JUNKIE curtisreed's Avatar
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    Could you not set your cam journals on vee blocks, take a height guage and find the height of the sections between lobes then the height of the heel and do the math?

    Curtis

  4. #4
    Senior Member RACING JUNKIE
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    Now why would you want to do it the easy way????

    (Great suggestion)

  5. #5
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    I thought you measure from the centerline of the cam to the heel of the lobe and multiply that by 2.

    TS1955

  6. #6
    Senior Member RACING JUNKIE curtisreed's Avatar
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    Quote Originally Posted by TS1955
    I thought you measure from the centerline of the cam to the heel of the lobe and multiply that by 2.

    TS1955
    You could if the cam were cut in two and had a point in the center to measure from.

  7. #7
    Senior Member RACING JUNKIE curtisreed's Avatar
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    Quote Originally Posted by oldandtired
    Now why would you want to do it the easy way????

    (Great suggestion)
    Thanks, I guess everyone just happens to have a surface plate, vee blocks and height gauge laying around though huh? I run a machine shop so sometime things seem easier to me than they would be for others.


    Curtis

  8. #8
    Senior Member RACING JUNKIE
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    Doesn't make sence too me why you guys are making this so hard :shock: If the cam is installed, all you have to do is set up a 2" travel indicator (you do need to know the exact cam lift) pickup the lowest point on the cam. Then rotate the engine to the highest lift C/L. Then subtract the lowest point form the highest point, then subtract the total cam lift, you then have the base circle dia.If you don't have a 2" travel indicator use a 1" and set a 1/2" spacer under the indicator at the lowest point. If the cam is not installed, you can generally mike/measure across the C/L of the cam, since most cams donot start the lift before the halfway point on the cam (this won't be exact but will get you close enough to tell if you have a small BC cam or not) I too am a machinest for over 50yrs. and have a surface plate in my home shop and micrometers 0 to 12", plus a 1/2 doz. indicators, dial bores,Height gage, etc.

    Just my 2 cents

    Zip.

  9. #9
    Senior Member RACING JUNKIE curtisreed's Avatar
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    Quote Originally Posted by zipper06
    Doesn't make sence too me why you guys are making this so hard :shock: If the cam is installed, all you have to do is set up a 2" travel indicator (you do need to know the exact cam lift) pickup the lowest point on the cam. Then rotate the engine to the highest lift C/L. Then subtract the lowest point form the highest point, then subtract the total cam lift, you then have the base circle dia.If you don't have a 2" travel indicator use a 1" and set a 1/2" spacer under the indicator at the lowest point. If the cam is not installed, you can generally mike/measure across the C/L of the cam, since most cams donot start the lift before the halfway point on the cam (this won't be exact but will get you close enough to tell if you have a small BC cam or not) I too am a machinest for over 50yrs. and have a surface plate in my home shop and micrometers 0 to 12", plus a 1/2 doz. indicators, dial bores,Height gage, etc.

    Just my 2 cents

    Zip.
    If it is installed you are exactly right. I never even thought about it being in the block. ops: ops: Zipper you win I've only been in the game 25yrs :lol: :lol: . If you guys saw the cnc program I've been working on, my brain fade would make some sense. Glad you chimed in for the guy Zip.

    Curtis

  10. #10
    Senior Member RACING JUNKIE
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    Quote Originally Posted by doorracer
    Quote Originally Posted by zipper06
    Doesn't make sence too me why you guys are making this so hard :shock: If the cam is installed, all you have to do is set up a 2" travel indicator (you do need to know the exact cam lift) pickup the lowest point on the cam. Then rotate the engine to the highest lift C/L. Then subtract the lowest point form the highest point, then subtract the total cam lift, you then have the base circle dia.If you don't have a 2" travel indicator use a 1" and set a 1/2" spacer under the indicator at the lowest point. If the cam is not installed, you can generally mike/measure across the C/L of the cam, since most cams donot start the lift before the halfway point on the cam (this won't be exact but will get you close enough to tell if you have a small BC cam or not) I too am a machinest for over 50yrs. and have a surface plate in my home shop and micrometers 0 to 12", plus a 1/2 doz. indicators, dial bores,Height gage, etc.

    Just my 2 cents

    Zip.
    If it is installed you are exactly right. I never even thought about it being in the block. ops: ops: Zipper you win I've only been in the game 25yrs :lol: :lol: . If you guys saw the cnc program I've been working on, my brain fade would make some sense. Glad you chimed in for the guy Zip.

    Curtis
    Uh,Oh, looks like i screwed up ops: what i said will give you the cam lift but want give you the BC without knowing where the centerline of the cam is. Sorry i was half asleep. ops:

    Zip.

    PS Curtis, CNC programming and operating CNC equipment is also what i do for a living when i work, at a plastics injection mold building com.


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