The link TeleDoc posted is broken for me. This one has always worked for me: http://pictures.olsenstoy.com
They have been in business a long time, and you never hear a bad word about them, except sometimes it takes a while for an order to get filled. I absolutely trust their website. I don't know why it says you need an extension, though. I am using the latest version of Firefox, and it is working first try.
On the Olsen's site, look for the "Library" link near the bottom of the page. On that page, click, "Enter the library." There, you will see all the categories of engines they have the drawings for. Yours is at the top, "Lionel Postwar Locomotives", click and then scroll down to find the 736. Or just use the link I posted yesterday - it goes the same place. The drawings are .pdf's, so you will need to use Adobe Acrobat or similar to read them.
You said earlier that the whistle was blowing continually. This makes me think that the problem may not be the engine itself. The whistle is in the tender (coal car) - that's why you should try running just the engine by itself. Or, there could be an electrical problem in the transformer that is causing the whistle to blow when it shouldn't, which is why you should try a different transformer, too.
Repairing old trains can be intimidating, for sure, but it is also very rewarding. And, they are pretty simple machines, really. Some tips:
1) Olsen's site has a lot of additional information on servicing locomotives in the section "Lionel Loco Service Info" (just below "Lionel Postwar Locomotives" in their Library). It makes for a good orientation and helps you understand what you are looking at.
2) I use an old baking sheet (the type you bake cookies on) to put the engine on when working on it. This prevents dropped parts from rolling off the table, never to be seen again. And a rolled-up old towel to protect the paint on the engine.
3) As you take things apart, take pictures. You'll be glad you did when you go to put it back together!
4) Use screwdrivers that fit well into the slots in the screw heads. Too big or small and you can mar the screw, which looks bad, and makes it more difficult to use. For the same reason, use pliers that don't have serrated or knurled jaws.
5) When you remove screws or small parts, put them in separate ziploc bags, and put a piece of paper in the bag describing where they came from - e.g., "side rod screws"
6) Be extra attentive to how the side rods and connecting rods go together. If these are installed wrong, the mechanism will bind.
7) Clean the parts you remove of old oil and grease. I use old toothbrushes, q-tips, and toothpicks (the round ones). Mineral Spirits works well as a solvent (but don't use it on paint); you'll want to do this part outside.
8) Don't let it intimidate you. At the end of the day, it's just an electric motor bolted to some wheels!
