Joe wrote:
<I've been following the discussion related to Chucks engine problem
with interest. My question would be, why does the engine noise related
to valve clearance problems appear only when the engine is under load?
Do valves open further when under a load or at higher RPMs?>
Joe---Valves should not open farther any measureable amount, when
the engine is under load or at higher rpm.
< I don't fully understand the concept of "coming on to cam" (this may
be stated incorrectly)>
It's my understanding that this is when the torque numbers are at their
highest. With the stock cam it starts around 3,000 rpm. Performance cams
start producing greater torque at higher rpms. (Lots of variables here
as to how this is done)
< I ask this because I just put a modified head on my old short block
with a "mild" cam. Don't ask for specs, the po didn't "remember" what
cam he put in. I have a distinct rattle at 2800-3000 rpms. It sounds
like valve gear problems to me.>
It's very possible at what you're hearing is a pinging, brought about
from the higher CR from shaving the head. Higher rpms alleviate the
reason for is sound, as the flame front is a constant, but piston speeds
increase. Some relief for this pinging, or rattle, can be found by
using higher octane, retarding the ign. timing, or backing out of the
throttle a tad. (Lessening the load)
Dick
< The rattle seems to go away at RPMs above that, although I may not be
hearing it because of the exhaust racket. I can't duplicate the rattle
with the car sitting still, and it barely perceptable when I drive with
the top down. I had milled the head (only to 9.5:1). I bought PI spec
push rods anticipating that the stock US spec rods would be too long. It
turns out that the P! I rods are way too short, so I stayed with the
stock push rods. I still have a little room for adjustment. I bought
double valve springs, and I don't see any potential for binding. The
lifter clearances are normal, and the rocker geometry looks good. The
rattle sounds like valve lash to me. Otherwise, the car runs great. How
can I diagnose? Joe Davis >
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