I am resurrecting this post which I started last December because of a chuffing problem on my Polar Express LionChief Berkshire engine, set #78-4328. I delayed looking at this engine until after the holidays but now I have and I am still at a loss as to what is causing the problem. I have popped the hood on this thing and have looked for the components that GRJ suggested to check out. First of all I am not experienced with working on Can motors so I don't what I'm looking for. Anyway, I found the motor easily enough and the the flywheel which sits atop of it but I can find no tab or a chuff chopper, whatever that is. I turned the flywheel several revolutions but I observed nothing to tell me what is going on. I saw no tabs or anything else moving towards or making contact with the sensors which I think I see on the inside of a couple of the drivers(little red bulbs). If someone could specifically identify where these tabs are as well as the chuff chopper perhaps I could fix this thing but as it is I just don't know what I'm looking for. Any assistance would be appreciated.