One of the manufacturers used two cherry switches mounted ninety degrees apart to generate 4 chuffs from a two lobe cam. I think it was 3rdRail. Someone else on the forum may know for sure ? As for some chuffs sounding different it happens on real steam locos The valve linkage can be less than perfectly synchronized from one side of the loco to the other and one or two beats may be fractions of a second shorter or longer than the opposite cylinder. The timing, controlled by the eccentric crank, may be perfect from one side to the other however the cutoff can be slightly off. Such as, one cylinder can be at 40% cutoff and the other side at 45%. That was one of the reasons the Baker valve gear was designed to eliminate the uneven ware on the Expansion Link of the Walschaerts valve gear. j
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