September 2018
TeChnical TopiC
By ..Bob Schapel
T
T-TYPE ROCKER GEAR
he T-Type rocker gear is often nois-
ier than it should be. Fortunately,
some of the causes are easy to fix.
Valve clearances cannot be set accu-
rately if the rocker faces or cam-
followers are worn, or if the rocker shaft
is loose in the pedestals. When fitted to
an engine, the rocker shaft should be
firmly clamped in the four pedestals.
However, in many of the engines I have
dismantled, the shaft has had a worn or
“hammered” appearance where it
passes through the pedestals, indicating
that it has been “rattling” about. Rocker
gear is often ignored during engine re-
builds.
Rockers, pedestals, pushrods and cam-
followers should be numbered during
dismantling, so they can be reassem-
bled in their correct places.
The clamping effect of each pedestal
can be checked individually. With the
spacer and shaft in position, tighten a
“dummy” 3/8” bolt through the pedestal
mounting hole (or clamp it in the edge of
a vice). If the shaft is still loose, remove
the spacer and thin it down a few “thou”.
Repeat the process until the shaft is firm
in that pedestal. There are four pedes-
tals so don’t mix up the spacers! Don’t
thin spacers more than necessary be-
cause that could cause the pedestals to
crack across the top.
Inspect the curved rocker faces where
they contact the valve stems. If they are
worn or chipped, they should be re-
ground to the correct radius. Inspect the
cam-followers. If their bottom faces are
worn or pitted, they can be re-ground
because they are “chilled”, which means
the hardening is quite deep. It is proba-
bly best to get a good machine shop to
do these re-facing jobs. Inspect the
pushrods too. If any pushrods are bent,
they are probably polished on one side,
where they have been tapping noisily on
the “guide” tube.
OPTIONAL MODIFICATIONS:
Since about 1970, I have inverted the
rocker shaft when I work on T-Type
rocker gear. I turn the shaft “end over
end”, to keep the keyways on the cor-
rect side. This necessitates the drilling
of a new supply hole to allow oil from
the rear pedestal into the hollow shaft. A
tiny patch of case-hardening must be
ground off the shaft before it can be
drilled. This modification ensures that oil
is delivered to where it is most needed,
helps reduce excess oil flow through the
overhead valve gear and gives the
rocker bushes a “new”, unworn surface
to run on.
Unfortunately, re-drilling this supply hole
in its original position (on the underside
of the shaft) re-introduces a weakness
in the original design. Its location makes
it a major stress point. Many T-Types,
particularly race cars, have broken their
rocker shafts at this supply hole. To
overcome the problem, I now drill the
new supply hole through the side of the
shaft and grind a channel inside the rear
pedestal, linking the pedestal gallery to
the new hole.
(Updated from Bob’s 1970s MGCC
Magazine article.)
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