PROBLEM IN MEASURING VALVES: A previous TSO stated that when the rocker
arm tip wears, accurate adjustment using a feeler gauge is virtually
impossible. "You may think the clearance is correct, when in fact it may
be as much as twice the desired amount. The most accurate method
requires that a dial indicator be set with its plunger bearing against
the top of the rocker tip."
I have purchased a dial indicator with magnetic base. From the above
discussion about worn rocker arm, a feeler gauge reading would be LESS
than the reading by a dial indicator. I'm getting the REVERSE.
In accordance with John Twist's practice, I am setting my valves to
.015. I have set all valves with the dial indicator. Then I was curious
what the feeler gauge might read. It read MUCH GREATER values. In some
cases the feeler gauge read .020 and .024 after I had set them for .015
with the dial.
Why? What am I doing wrong? I mount the magnetic base on whatever metal
real estate I can find around the block. Then I position the plunger of
the dial indicator via the support arms on the tip of the rocker arm
that I am measuring, as close a perpendicular position as I can and with
the plunger depressed for at least one revolution of the dial to insure
constant pressure. With the rocker arm gap closed, I set the dial to
zero. I then open the rocker arm and read the difference on the dial. If
required, I turn the adjustment screw until I have .015 clearance on the
dial. I then triple check the measurement by opening and closing the
arm. If I then read the same gap with a feeler gauge without moving the
crankshaft, I get anywhere between .017 and .024. GREAT ERROR SOMEWHERE.
I have measured all feeler gauges with the dial indicator to determine
accuracy of each. There is no variance.
The plunger of the dial does not stick (brand new). Making triple
readings each time should reveal sticking plunger or slippage of the
plunger on the rocker arm.
I don't know what is going wrong. I suspect it must be the way I am
setting up the dial indicator, but I don't see the error. Any ideas
would be appreciated.
Stu Keen
51 MGTD MkII
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