CFisher@borgwarner.com wrote:
>
>Some questions though:
>With a .100" shaved head, about what ball park would the compression ratio
>be? I may do the measurements and math, but does someone have a general
>idea?
>
Can't say for sure without other dimensions. The compression ratio also
changes with the bore size. Does the engine have 83mm cylinders, 86mm?
87mm? Ballpark, though--it's now at least 10.5:1. The most accurate way
to determine the CR is to cc the chambers and calculate from the correct
volume.
>
>With that much off, how do people deal with insuffient valve lash? If you
>put in shorter push rods, doesn't that still leave bad geomitry that will
>side load the valves work on the heal of the rocker?
>
Yes, and no. In theory, installing pushrods shortened to the amount
that the head was shaved preserves correct geometry (i.e., if the head
is shaved 0.100", shortening the pushrods 0.100" is correct). There are
always small variations depending upon the rockers used. This is why
racers use tubular pushrods that can be shortened, and do each
individually. If you think about the geometry, the nose of the rocker
pushes across the top of the valve stem anyway--that can't be
avoided--because it's rotating around a fixed center, the rocker shaft.
Ideally, the pushrod should be adjusted so that the center of the rocker
nose contact point is over the center of the valve stem at peak valve
spring pressure, i.e., at peak lift, with the adjusting screw turned out
a fixed amount.
>
>Do people go to roller rockers?
>
I'm sure some do, but it's not necessary. In fact, they're more likely
to induce valve float in a stock-springed engine, because virtually all
of the roller rockers I've seen are heavier. Anyway, why spend $350 to
make an easily-fixed problem a tiny bit better. Still have the problem
is one of not enough valve lash--the root of that problem is still
pushrod length, not the rocker.
>
>Where would you get them?,
>
>or the shortened push rods?
>
Both BFE and Ted Schumacher have both, I believe. Both can supply the
pushrods pre-shortened to the correct length, I believe, if you know the
amount the head was shaved.
>
>
>
Cheers.
--
Michael D. Porter
Roswell, NM
Never let anyone drive you crazy when you know it's within walking distance....
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