I have had this K-Line Mikado for some time. I use it to pull my semi scale Western Pacific feather boxcars. My collection has grown to well over 20 cars and the engine was nearing its limit. A big part of the problem is the piston type smoke unit driven directly from the motor. These create a lot of drag and rob a lot of power from the motor. I finally got around to replacing the smoke unit with a fan unit. That of course required a new chuff switch to provide the 4 chuffs.
The gear that drives the piston gave me an idea. Its the same gear as the one on the axle so turns the same speed. Rather than install an axle cam I just had to drill and tap 3 more holes for screws to act as cams on a mechanical switch.
Here is before showing the piston attached to the gear.
After the gear mod.
And the result.