[DeTomaso] Stupid question

[Will Kooiman]

I have a stupid question that has been bugging me lately.

 

Why does a solid lifter camshaft require clearance (lash)?  In other words,
why can't you install it at zero lash - or at least near zero?

 

Of course, I know you can't, but why?  If anything is going to move around
at high rpm, it should create too much lash, not too little, right?  For
example, you're not going to hit 7,000rpm and suddenly have your pushrods
grow 0.250.  They might flex a little, or you might have valve bounce, but
that would increase the lash, not decrease it.

 

We all know, a hydraulic lifter camshaft has zero lash.  How can it get by
w/out lash, but a solid lifter camshaft can't?

 

Is a solid lifter camshaft installed with lash, because it can be?  (sorta
like the joke, why does a dawg lick. nevermind)

 

The reason it has been bugging me is because I was thinking about wiped
camshafts.  How many of these are hydraulic, and how many are solid?  All of
the incidents I can remember have been hydraulic.  Maybe solid lifter
camshafts are less prone to wiping because of the lash.  It makes sense
anyway.  Hydraulic camshafts get rubbed 360deg by the lifters.  Solids only
get rubbed about 140-150deg  (duration @ lash / 2)

 

A bonus question is, why do different solid camshafts require different
amounts of lash?  I'm guessing it's because that's what they were designed
to have.  Okay.  Why?  Why not grind everything for a lash of 0.020?  What
advantage would there be to grinding a cam for 0.025?

 

Another idea I had was to allow the lifter to build up some momentum to act
on the valve, but that's starting to sound silly.

 

Like I said, they're stupid questions.  Now you know what I'm thinking about
on the way home from work.

 

Will.