>Also I'd think that if you shim the cam towers you'd also need to increase
>the lash pad thickness by the same amount?
The short answer is yes but as was pointed out, that's hard to do with the
stock retainers. What you should do after shimming is check the cam/rocker
arm contact (wipe) pattern. You do this by putting machinists blue on the
rocker pad - in a pinch you can use black magic marker - and rotating the
cam once by hand over the rocker. Be sure that the lash is set to the
correct cold spec. Take the rocker arm out and look at the area of bluing
that has been wiped away. As long as that area doesn't go over the edge of
the rocker pad your okay. It should be even side to side too - square that
is. Shimming the towers will move the pattern to the rear of the rocker -
away from the valve - which is an old trick for increasing valve lift.
Moving the cams contact point with the rocker arm back effectively increases
the rocker arm ratio.
If you check this and find your pattern is beginning to go over the edge of
the rocker pad their is one other way to correct that without going to the
expense of new retainers and lash pads. Assuming you've got the head off,
you can do a valve job. Let the machinist know what you're trying to do as
he will need to cut deeper into the seat than he normally would to create a
nice seat surface. As you cut material off of the valve seats and/or the
valves, the valves will sit deeper into the head. It's usually referred to
as seat depth. As the seat depth increases, the valve tip height increases
also which gives the same effect as adding a thicker lash pad. The
difference here is that the valve spring installed height also increases.
There is a limit to how much you can grind away on the seat but you should
be able to correct any problem with the wipe pattern unless it's excessive.
Brian
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