Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Please do not use Bondo or BOG.
Here are the reasons:

It is weak.
It actually absorbs liquids promoting rust
I doubt it stands up to heat.

Why should you use JB Weld?

It is strong 💪
It resists almost all liquids
It stands up to heat
It is cheap and easily purchased

I've repaired motorcycle blocks with JB Weld. Example: On my '56 Norton, I made new fin to replace some broken ones. After a dozen years, it's still repaired.