NoShortcuts (9/14/2013)
I'm rusty on these, Alan.
I vaguely recall that Thomas made two ratios of rockerarms for the y-blocks. Seems like one offering was 1.8:1 Yes, they were magnesium and amazingly light. I had a set of the lower ratio ones, but can't remember if they were advertised as 1.5:1 or 1.5 something:1 or 1.6:1
In looking at them, I felt that they looked rather fragile. There was little physical mass to what I believe were castings. I guess I didn't appreciate the strength of magnesium! I never used them, but sold them to a friend-of-a-friend in Texas nearly 40 years ago.Flashback...
Another aspect of the Thomas rockerarms that resulted in my never using them after purchase was the valve lash adjusting hardware. While the adjuster stud and locking nut were the same style used by FoMoCo on the '54, '55' and '56 rockerarms, they were no where near equivalent in diameter. Dainty in comparison! I don't know how they could have been smaller, but that's how I remember them (from 40 years ago)!
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York