Sorry, Stuart, but the only way to find out if the tappets are worn, is
to remove them. Remove the rocker arm assembly, extract the pushrods,
remove the tappet cover, and inspect the tappets, one by one. Look at
the bottom of the tappets, for pock marks. Have them resurfaced, should
you find wear.
The spring pressure for the valves only needs to be 90 lbs, to seal the
combustion chanber. TC-early TD heads had 123 lb total pressure exerted.
Late TD-TF valve springs increased this pressure to 150 lbs pressure
exerted. The factory thought that the springs were not strong enough, as
they saw shiny metal marks on the valve springs. They thought that the
engine was experiencing "valve crash." Analysis in the 1990's found this
to be valve springs were going into oscillation, at about 3600 rpm.
With the increased spring pressure, the weak link in the system receives
the most punishment. In this case, it is the tappets. Reduced spring
pressure will result in longer tappet life. Brown & Gammons sells a
bucket tappet, providing better (sic) lubrication at the lobe to tappet
face. Skip Kelsey used to sell "Silver Bullet" tappets, better than
original.
John Seim
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