Camshaft profile - direct measurement?

[Paul_D]

Good evening all,

I set up v-blocks, a degree wheel and dial indicator planning to take some measurements from a couple pair of cams. The amount of lift, measured directly off the cam lobes is considerably less than the specified valve lift in the various reference sources I have. I was assuming the rockers were symmetrical and that lift of the cam lobe would equal the lift as measured at the valve stems . This is not the case, it seems. Is there a ratio to the lengths of each arm of the rockers, or a constant multiplier that can be used to convert lobe lift to actual valve lift? I'm lazy and it's so much easier to check the cams in v-blocks than to set them up in a cam housing with rockers, valves and head(s). It would be nice to have this work.

Thanks in advance for any help with this.


Paul
'71T coupe

[aigel]

Paul,

The ratio is somewhere around 1.4, 1.45, depending on who you ask.

http://www.elgincams.com/c-por2.html
source for ratio of the rocker-valve arm to the rocker-cam arm lengths = 1.4 to 1.0

If you read the second link you will learn that the ratio is not fixed as the contact point of the cam lobe to the rocker swipes across the rocker face. So this also changes with the cam profile.

Hope this helps,

George

[jcge]

Try this link

[Paul_D]

Excellent. Exactly what I needed to know. Thank you George, and jcgce. For my purposes 1.45 will be fine.