Tappets have been a problem for some time. We will not install any tappets
that have not been hardness tested. The minimum hardness that we will
install in a street engine is Rockwell C scale 51, and for racing we like to
use tappets that are harder than 56 Rc. We send a lot of tappets back to
our vendors as defective.
When we have tested original (installed by Leyland) tappets, we have
generally found them to be in the 52 Rc to 55 Rc range. The replacement
tappets available today have varied from 19Rc all the way up to 60 Rc. The
last batch of "Triumphtune" tappets went from 41 Rc up to 56 Rc. They all
look the same. They are made to go on a cam that does not have tapered
lobes. We have found that if the lobes of the cam are tapered and the
tappets are machined to match and are hard enough, with the proper break in
and use of Moly based assembly lube, the failure rate is almost nil. We use
Kendall GT-1 racing oil in our race engines and Chevron in our street
engines. The Kendall is superior to most other oils in keeping iron to iron
wear to a minimum. It is also excellent where there are bearings. Other oils
we have tried have worked well in the bearings and crank area, but not
wherever there is iron to iron, non pressure lubed situations. These areas
are the cam and tappets, the rocker shaft, valve stem to rocker arm, timing
chain to tensioner, and cam to oil pump drive gear.
These experience are based on TR-3, 4, and 4A engines and may not apply
exactly to TR-6 and Spitfires.
Regards, Greg Solow
The Engine Room
Santa Cruz, Ca.
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