Re: This engine has "three barrels" and it's even painted green!

I believe that the outside cylinders are timed 120 degrees and the center cylinder timing is offset somewhat to account for the inclination of the third cylinder. The third cylinder is, I believe, inclined to avoid interference with the various bits of the lead truck and equalization.

I will happily admit to being profoundly ignorant on a great lot of subjects, and will not claim the Wikipedia is infallible. The following is excerpted from an article about the locomotives of the LNER Gresley Classes A1 and A3 as typified by The Flying Scotsman.

"... The 1470-class Pacific was the third Great Northern locomotive type to incorporate Gresley's universal 3-cylinder layout. All three cylinders drove the middle coupled axle. The outside cranks were set at 120°, with the inside crank displaced by about 7 degrees to allow for the 1:8 inclination of the inside cylinder. Gresley conjugated valve gear derived the motion of the inside valve spindle from the two outside valve spindles: this eliminated an inaccessible middle set of valve gear between the frames."

Rex Beistle
NMRA RMR
Estes Valley Division