Super Glue

I have successfully used CA glue to repair a broken pilot on a die cast prewar Lionel steamer.

Personally, I haven't had much luck with the brand name: "Super Glue", and would stay clear of any dime store adhesives. I used CA glue purchased in a hobby shop.

That written, these days I'd use JB Weld 5 minute epoxy. The last cowcatcher I glued, on a blue modern era Lionel steam body marked 1989, has held fine after several years.

Depends on the shape of the part that is broke off. A rather loose rule of thumb is if the part protrudes further from the break than the break is wide superglue (CA) is likely to fail. Surface area is all important.  A technique I have used is to use CA to tack the part in place then on the underside build up a layer of JB weld possibly with a metal stiffener embedded in the JB weld.  Something that will make any glue joint stronger is if the mating surface is rough rather than smooth. However broke metal may have a granular surface in the break, in this case you cannot file or sand as you want the undulations of the two surfaces to mate they increase surface area and the many facets within the break contribute to a mechanical bond. One technique I have used is to etch metal in the area of the break with a mild acid. Phosphoric acid works on many metals, the trick is how much to dilute and how long to leave it on the surface. It must be thoroughly washed off after appropriate etching before you attempt to glue. Your looking for a uniform dull satin finish with no mirror like shiny highlights.  Regardless of the type of glue this will provide the best adhesion and not interfere with the parts nestling back toghther. The great thing about the CA glues is they allow parts to nestle into one another better than any of the thicker glues such as epoxy. However CA is brittle and will fail under shock loads or even temperture fluctuation where the joint is expanding and contracting.   On the other hand epoxy is many times more flexible but may not allow the parts to fully nestle together. Another rule of thumb is that the fast cure epoxys are not as strong as the slow cure though the difference is not as great as thirty- forty  years ago. The first five minute epoxy I tried was nearly useless, it never got hard enough to form a strong bond.  Can you make some photos of your problem ?     That would help determine an effective strategy to bond the break.  J   

You have to purchase super-glue accelerator, of which there are several brands and use the "thickened" version. Spray on after mating parts Works well with casting fractures. Immediate clamping with absolutely no movement. For sheet metal, as a prelude to epoxy or J,B, Weld.

Accelerator causes CA to foam and weakens the joint. If you have a broad joint you can afford some weakening. You can speed up the cure a good bit by huffing your breath on the surfaces before applying the CA.  J

I was able to glue a cast handrail stanchion on a newer 8024 Steam loco.

Wrapped rubber bands around the handrail so it was pulled closer to the boiler

Rehearsed the fit a few times - and a tiny drop of Krazy Glue. (also recommend avoiding bargin brands)

Also glued a piece of the apron/plow that broke off.

Worked like a champ.

another JB Weld user

I have used JB-Weld to repair a number of diecast locomotive shells, the pilot is the favorite thing to break off.   I try to find a hidden area that I can build up a little out of sight to increase the strength, sometimes hard to do, depending on where the break is.

Jb weld is my go to. Super glue for marker lights applied on toothpick first.

Have to say JB Weld is strong as year back i had a crack in the oil pan on a 1994 jeep cherokee, drained oil and wiped the bottom clean with acetone.

While under the jeep applied JbWeld to 3 inch crack never leaked for a good many years until it's body panels rusted out and had holes in floor then was scrapped.

The straight 6 cylinder motor had almost 300,000 on it never failed and outlived the body of jeep.

Wow! Thanks for all of the input. Now I should provide more specifics. I don't have the engine but I am trying to decide how much if anything to offer. The broken piece is from the cab roof corner. It is a prewar loco. It was very nicely repainted (not in black) but it looks like it was dropped. I think JB Weld dries noticeably gray so it would stand out or require repainting, which would require the removal of trim pieces, which I am afraid could result in damaging the locomotive casing. ( And I would likely hand all this work over to someone else, since I have no skill or time for such endeavors.) As an alternative, I was considering a quality super glue (I'm thinking, Loctite gel) that would dry clear and leave a less noticeable thin repair line. I was also thinking about using either a small strip of brass or metal tape, glued on the underside of the failure line to stiffen the repair.

Am I out to lunch or does this seem like a workable approach? Thanks!

Truthfully, any repair is probably going to need to be repainted to look right IMO.

could you post a pic of the damaged area?

Unfortinately, I do not have the engine so I can't post a picture. But it is a very acute triangular piece from the back end of the cab roof. I tend to trust John's thoughts and have to assume it will require repainting.

Flexible c.a. glue is a better product at resisting shock and it comes in black. Try Woodcraft, Klingspor, or Starbond in California (they ship quickly). Comes in one or two ounces.