I by far am no expert but in my experience, you usually will not see any
pistons with 4 rings anymore. This method was used on much older
engines to help stabilize the piston because of the much longer skirts
used back then. When they started cam grinding pistons, there was no
longer a need for them. I work on tractors as a hobby. I am restoring
a 1929 Caterpillar crawler tractor which uses 4 rings. Low compression,
low rpm, but large piston skirts.
I guess since the Triumph engine is an off shoot of the Massey engine,
that might have been carried over.
Pat in NC
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