I agree on the ST34 also mine is converted to diesel with a Davis head one of the sweetest running engines I have the ring is great after lots of time you replace a ring not a piston
and liner and plenty of compression as a diesel no bad habits and it is BB crank
my ST40 has been around years also with a Davis head and no issues ever martin

a little castor good in any engine and no plating to peel in a steel liner