Polar Express LionChief Chuff Sounds - Intermittent Sound

Not ideally normal but normal.

Chuff sound is triggered by a cam on the front axle driving a lever, and then one end is an optical flag, the front end is the piston in the smoke unit.

#1 there is very little tolerance in the system of the optical sensor. The flag has to clear the sensor and then block the beam.

#2 a known wear point is the cam lobe follower- a small piece of plastic that rubs agains the cam and transfers the up and down motion to the lever. As it wears against the cam it becomes shorter and this affects that very tight tolerance in the optical flag

#3 the lever is hardened steel and may not bend if trying to adjust and often snaps right in half if you try to bend

#4 The lever system also may depend on the smoke unit piston and return spring. The plastic piston may bind in the smoke unit bore and not return and be stuck in the up position.

So again, normal IMO. The fact it works at low speed reliably implies the system is still within good tolerance and high speed, you are just getting cam float, where the system of the lever is slower than the cam, but in this system, that just reduces the stroke and skips thus not triggering chuff.

Also, test with the whistle or announcements. If just chuff is the only sound function lost at high speed, but the speaker is working and no loss of other sound functions then again it's chuff sensor just not getting triggered and while you could go down some rabbit hole of chasing that problem, more importantly, this hopefully is not a drawbar connection issue. If a suspected drawbar issue where all sounds cut out, then that is a much more urgent potential problem. Just trying to cover all bases.

Wow, that’s a LOT to digest ( for a novice ); but thank you for sharing your (obvious) expertise.

I did verify, all the sounds (bell, whistle, announcements) work at full stop and at all speeds from slow to fast.

Your suggestions are a bit hard to follow without illustrations, as I’m not fully versed on some of the terminology.  I’m guessing this isn’t a fix to be tackled by anyone but an expert?  Any idea what a diagnosis and repair would cost?  The whole set was around $350.

Thanks again.