How do you mesure base circle?

Old 04-14-2009, 06:09 AM
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FullTimeRacing
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Default How do you mesure base circle?

How do you the mesure base circle on a cam? ops:
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Old 04-15-2009, 07:07 AM
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oldandtired
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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
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Old 04-15-2009, 09:12 AM
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curtisreed
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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?

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Old 04-15-2009, 10:37 AM
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oldandtired
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Now why would you want to do it the easy way????

(Great suggestion)
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Old 04-15-2009, 10:38 AM
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TS1955
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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.

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Old 04-15-2009, 01:10 PM
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curtisreed
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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.
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Old 04-15-2009, 08:10 PM
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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.


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Old 04-15-2009, 09:14 PM
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zipper06
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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.
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Old 04-16-2009, 05:10 AM
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curtisreed
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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
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Old 04-16-2009, 08:11 AM
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zipper06
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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

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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