Whats the technical reason for valve lash.

[tbird]

It seems you could run a .001 or 2 lash warm for adjustment purposes only. But realistically there are some mechanical factors some where like maybe cam flex and valve train harmonics.
Im just curious what the reasons for lash are ,and what determines the lash amount for different cams.

[Jay Allen]

and what determines the lash amount for different cams.
I am sure you already know why we run lash a SR cams. But how much lash can be a diffulcult thing to nail down.

Lash at the cam X Rocker Ratio = HOT lash at the valve

Most common OTS cams and the stuff you are going to get at most places from a *cam tech guy* have very smooth opening and closing flanks. On your comic book cam card it'll say to run .0xx" of lash. Order a *custom* cam using book lobes. Order it for a SBC and 1.5 rockers. Now order the same cam for a BBC and 1.8 rocker arms. The lash on the card will be the same. That is not possible. Then in most cases you very from that lash +/- .002" to .004" and cranking compression is not affected much. (I pay very strict attention to that.)

So to answer your question, UNLESS you know what the intended lash at the cam was to be -AND- you have a Cam Dr file and you can see what the cam is doing from .001" to .006" to .010" to .015", its pretty hard to say what is REALLY going on.

[Willytucker]

Jay, I am not really sure how to interpret what you have said regarding OTS cams. Are you saying that you should take what the manufacturer says for lash as gospel due to the R&D they have put in or are you saying that it is simply a safe starting point and there is value in "dialing it in" so to speak?

[Jay Allen]

I guess more to the point, lash typically doesn't make that much of a difference with an OTS mechanical lifter (roller or solid). Now there are lobes from Comp/Cam Motion, etc that lash will make a difference. But those lobes are few and are far between.

The tech guy on the other end has the opening and closing velocities in front of him. It is his job to get you a cam that will not beat up parts and to get you a cam that is user friendly. The tech guy has never met you and is not aware of what your skill level is or isn't. This they must air on the side of caution.

Does it make more sense now?

[Willytucker]

Yes Jay, thanks.