How do you mesure base circle?

Old 04-16-2009, 09:09 AM
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I used my mic and got over an inch 1.020
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Old 04-16-2009, 10:47 AM
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Originally Posted by zipper06
Originally Posted by doorracer
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

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.

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:


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.
Hey I bought it. :lol:
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Old 04-16-2009, 11:25 AM
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here is what I do :roll: :roll: put it in the block and roll it over , if it don't hit nothing then you are good to go
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Old 04-20-2009, 06:43 PM
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The closest way to check it with dial calipers is....

Measure a cam journal and divide by two to find the centerline.
Then measure down from the cam journal to the base circle of the lobe.
Subtract this measurement from 1/2 the jounal diameter. This gives you the base circle radius.
Multiple that by 2 to get the base circle diameter.

Again, this is only acurate for +/- .002" or so.

Works well on a surface plate with V blocks and a digital indicator that reads in tenths (.0001)
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Old 04-20-2009, 07:08 PM
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If you're on a surface plate with v-blocks, just mic. the bearing journal, divide by 2,= C/L keep that number. Put your drop indicator on top of the cam bearing journal, set (0) then drop down the the heel of the cam. take that number from the kept number and multiply the what's left by 2 and you have the base circle.

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