I don't want to be offensive, but you complained earlier about people not responding to your requests for help. Let's analyze your last post and see what might be the problem.
First, the only description of the item with issues is an "Alco S-4." People that might want to help you need more to go on than that. How about indicating manufacturer, product number, type of operating system (command or conventional) and any other detail that might be relevant to the situation? Providing assistance should not require the assister to be a detective.
Second, you say that the "middle of the cab had melted to the smoke unit." Now, that may certainly be the case, but I'm not aware of many smoke units being positioned close enough to an engine cab to cause melting, particularly when discussing diesel engines. Could it be that you meant the engine body or hood had melted? In any regard, pictures of the damaged unit would have been very helpful in at least starting a diagnosis.
Third, your last post had nothing to do with the original thread except the commonality of model engine problems. Perhaps a new thread, titled "Bad Smoke Unit?" would get some suggestions of how to diagnose and fix the problem?
You are correct that many more people will look at concise thread titles, but they have to be a little more descriptive than just a product number. I first looked at this thread because I thought some Lionel product might be for sale.
Just my 2 cents.