The Razorback Traction Company's pantograph equipped ex-Bethlehem Steel 0-6-0 switcher, Lil' Stinky II, wasn't blowing smoke the way it should, so a quick teardown was in order...
Turns out the problem was the fine plastic flapper valve on the smoke piston:
Fortunately, I had a spare piston on hand, purchased by mistake a year or two back:
After straightening the flapper as best I could, the original piston was placed into the parts box for future use.
With the new piston, Lil' Stinky II is smoking up a storm!
Here's the original part number for a replacement piston. Near as I can tell, Lionel doesn't sell the flapper by itself, but the piston is reasonable enough at $5 or so plus postage.
Mitch