How is the chuff triggered on the Lionel PRR T1, scale TMCC version (6-28063)? 2 magnets inside a driver?
There is a 2 lob cam on one of the axles which triggers a cherry switch for the chuff.
As an aside, I have seen (here on the Forum?) some time ago a few photos of someone's project where he added - using epoxy, built up - 2 more lobes to the cam of a steamer, giving a proper 4-chuff. If you can get to it well enough, it seems like a reasonable thing.
Durable? Not sure - epoxy is pretty hard, and a micro-switch spring typically resists little.
You know - would a 4-lobe cam have been too much to ask?
The drivers have a convenient reassess on the back face where magnets can be attached without interference with the chassis. I installed two sets of four on each engine to experiment with generating four chuffs times two. Not really worth the effort seeing as the driveshaft solidly links both engines so there is no variation in driver rotation as per the real thing. The two motored LionMaster version would be better suited for such things.