Like friendship, JB Weld is magic. Rumors persist of shade tree mechanics in the Yukon repairing cracked engine blocks with JB Weld, and last month this theory was proved correct. [Project Farm] over on YouTube took a grinder to the head of a lawnmower engine, filled the gouge with JB Weld, and ran the engine for twenty minutes.

However, as with anything mechanical that doesn’t have a foul-mouthed Canadian in it, arguments ensued. ‘This was not a true test of JB Weld repairing a cracked engine block’, claimed Internet commenters, ‘I won’t even watch the video because the idea alone is click bait.’

Now, [Project Farm] is back at it. Is it possible to use JB Weld to cast an entire cylinder head for a lawnmower? It sure is. With a cast epoxy cylinder head, this engine will run for just long enough for a proof of concept.

This experiment began by casting a single monolithic block of JB Weld that’s a bit larger than the cylinder head for a lawnmower. After curing, this JB Brick was surfaced on both sides with a belt sander. No, there was no vacuum chamber or any other techniques used by people who work with epoxies for a living. With the brick surfaced, the head gasket was used to place the bolt holes, the brick was tapped for a spark plug, and a bit of the inside was Dremeled out for the valves.

After attaching the JB Weld cylinder head to a lawnmower, [Project Farm] ran the lawnmower for about a minute. Is this a proof of concept? Yes. Did it work? Absolutely. Is it the ultimate test of JB Weld and the myth of the cracked engine block? Unfortunately, no. For that, someone will have to build a real engine entirely out of JB Weld. Until then, just check out the video below.

Thanks [Xavier] for the tip.