JB Weld Fixes Cracked Cylinder Heads

There are persistent rumors that the main ingredient in JB Weld is magic. This two-part epoxy that you would normally find on a shelf next to your basic 5-minute epoxy, Titebond, various cyanoacrylates, and Gorilla glue is somehow different. Stories of ‘some guy’ in the Yukon using JB Weld on a cracked engine block abound. These stories are of course met with skepticism.

Now, finally, we have evidence you can use JB Weld to fix an engine. [Project Farm] over on YouTube gave it the ultimate test: he took the cylinder head off a lawnmower, took a grinder to the head, and patched the hole with JB Weld. The head had good compression, and the engine actually ran for 20 minutes before the test was concluded.

If this were a test of a field repair, it would be a test of an extremely crappy field repair. [Project Farm] made no attempt to ensure the piston didn't make contact with the blob of JB Weld, and in fact, there was some slight knocking from the piston tapping against a blob of epoxy. Still, this repair worked.

While this serves as proof of the feasibility of repairing an engine block with JB Weld, there is one ultimate test of JB Weld epoxy: build an engine out of it. For years, I’ve been casting my leftover JB Weld into a small square plastic container. In a few more years, I’ll have a block of JB Weld ‘stock’, large enough to machine the parts for a small (.049 cc) glow engine, like what you would find in ye olde tymie model planes and cars. Will it work? I have no idea, but now I can't wait to find out.