Casting Cylinder Heads Out Of JB Weld

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.

57 thoughts on “Casting Cylinder Heads Out Of JB Weld

    1. If you want production level equipment you are on the wrong website. If Walmart/Hazard Fraught/Crappy Tire ever thought they could sell non-metalic engines you know they would do it in a heart beat.

  1. Back in the day I heard someone say there exists an entire V8 engine made out of high temperature plastic. Didn’t pursue the claim any further.

    But why not? A bit of soot from excess fuel will work as an ablating surface so as long as the bulk of the plastic remains cool enough not to creep, and you don’t run the engine very hard, it should work just fine. People have made pistons for motorcycles out of wood that worked perfectly well for thousands of miles.

        1. “…to keep the oil and water inside…”

          Didn’t work (oil) for VW air-cooled Beetles, or ANY original British motorcycle.
          All that air-management shrouding around the VW engine? Just there to keep the leaks from the newly-added oil off the showroom floor. Only after you got it home had the oil accumulated past the point of being stopped by the shrouds.

          I and several of my rider-buddies used to protect our shifter-foot shoes from oil-drench by wearing baggies over them when we rode Nortons, BSAs, Ariels (remember the Square-Four? Never mind), Triumphs, Royal Enfields…it didn’t matter. It was 20th- century English Plague. But it made for onewaterproof shoe, anyhows.

          1. The big problem with British bike engines was the vertically split crankcases. That left a lovely big seam for the oil to drip out of. The Japanese bikes had horizontally split crankcases, that kept the oil from having an easy way out of the engine.

    1. plastic engine, there was a polymotor, a four cylinder car engine produced twenty or thirty years ago in an effort to make a lightweight engine. it has steel cylinder liners and a metal liner for the cylinder head. the block was so light you could pick it up and run with it. i still have some information on it stored somewhere

        1. The engineering department at Oregon State University had one, I think the test mule was a K car, the community college I attended had a chassis dynamometer, they used to test the engine and monitor it, was in the mid 80s if I remember correctly (I only heard about it second hand). Supposedly it was a module with a few bolts that held it in, a wiring connector, and ports for fuel and coolant, and the thing was designed to go 100,000 miles with no maintenance and you’d basically unplug it, lift it out, drop a new one in and connect it up, and it was supposed to take like an hour or something like that. Apparently one of them went the equivalent of 300,000 miles, but was under lab conditions. Wish I knew more about it.

  2. Sparkplug isn’t grounded through the head as an aluminum head would be. You can see the spark jumping the gap between the large washer and the head bolt to the right.

  3. I wonder if the design could be engineered to use JB Weld. My initial thought would be to bond a thin sheet of metal to the interior of the head and add a heat sink to the outside that is in contact with the inner sheet.
    Essentially tin foil with a tin foil heat sink supported by JB Weld.

    JB Weld owes this guy some free samples.

  4. That is surprising. Good hack!
    When I was a student I repaired a cracked cylinder block with epoxy. I wrote to Ciba-Geigy telling them I was an impoverished student and planning to do this repair, and what did they recommend. I got sent 2 tubes of some epoxy free.
    I took a ball pein hammer to the crack to complete the fracture, cleaned up the edges, stuck it all together, and the car was still running fine 2 years later.That was over 40 years ago BTW.

    1. Now that is a hack. What a great testimonial. I am sure there are many, many other cases similar to your that we never get to hear about. I once fixed my college roommate’s car when we got stranded on a trip from KY to N.J (900 miles) at about halfway. We walked to an auto parts store, bought some epoxy, and I glued the rotted and busted and leaking metal tube coming from the radiator to the intake manifold. It had been spraying coolant everywhere. We went and ate lunch…filled the radiator with water, and made it the remaining 500 miles home. I ran into him about 5 years later and asked him if he ever got his car fixed and he told me…he left it like it was and drove it for another 4 years before selling it. Epoxy rules.

  5. Lol, glad someone tried, tired of hearing that line.

    I do love the jb, especially the marine one as it can handle a lot more abuse/heat/chems than the normal one for whatever reason. Normal one tends to crumble after some months of acidic environments and mild heat.

  6. Good enough for the Federal Gummint…

    Howard Hughes’ Spruce Goose (HK-1) was certified as having been ‘airborne’, and therefore ‘airworthy’, by virtue of the fact that, with Mr. Hughes at the controls of the eight-engined seaplane, the plane flew at an altitude of 70 feet, for approximately one mile, in 1947. After reaching seventy feet, which some critics have attributed more to ‘ground effect’ than to good aircraft design, no attempt was made to try to climb. This first flight of the HK-1 was the only flight.

      1. Because like the Goose, this cylinder head only functioned for a minute or so. It’s highly doubtful it would have worked for much longer, as the ~500F heat resistance of JB-Weld is well below the temperatures faced inside a gasoline powered IC engine. JBW can last as a crack repair because some of the epoxy will be far enough from the combustion facing surfaces to be cool enough to survive, will maintaining the gas tight seal, but an entire engine component like this is going to quickly deteriorate in use.

  7. Not surprising it works. Many videos of cylinder heads made of acrylic to show the process on high speed video. It works. Not sure how long it will laskt but it works.

  8. I don’t see why a low RPM, low torque engine that has metal sleeves in the cylinder and maybe a metal inner cylinder head couldn’t last for a long time made out of JB weld. Being water jacketed cooled would keep the main areas at low temps and the operating temperatures are within range for the rest of the engine for high temp plastic. I doubt the epoxy is any different. As long as things like bearings and the main crank are actually steel – it could run for a very long time I bet. Things like the main fly wheel might be an exception though, and the starter bendix engagement on the flywheel is pretty rough on say a car, even on steel, but if you could used a compression release while getting the engine up to starting speed it would take a lot of wear off the thing.

  9. Maybe someone here has better Google-fu than me, but I distinctly remember reading, with my own two eyes, a “cracked block repair” testimony from a J-B Weld customer. That is, it wasn’t a “rumor” in the usual sense of the word, but a claim in product literature of some kind – the back of the package maybe.

    The claim was to repair a tractor engine, saving the owner about $2000, but I can’t find the actual reference anymore. An image search turned up nothing I could be sure was authentic; closest result I found was a screenshot, presumably from a website, of text substantially similar to what I remember having read.

    In any case, no way in hell would I try to repair an engine with any kind of epoxy, much less build a cylinder head out of it. :-)

    1. It was the back of the package. I think over the years different stories are added and removed. It’s been a few years since I bought JB but from what I can remember, a caterpillar engine, garbage disposal and farm equipment have all appeared

  10. Richard Petty used JB Weld cylinder heads to win the 1963 Daytona 500. Well, OK…he didn’t. But, he could have, ha ha. This was a great test and, it worked so..I take my hat off to this fellow.

  11. Silence the haters that said jb weld can’t make a head as the benchoff clickbait shouts, well nobody actually said it woudln’t work last time, just that it was a stupid idea if you wanted the thing to last robustly. It was even more effort and expense to make a head from jb weld than buy a offcut of aluminium plate and make your own head, its the absolute definition of clickbait now, doing things the dumb hard way to generate views.
    Hats off benchoff, you’ve raised the bar once more.

  12. ” For that, someone will have to build a real engine entirely out of JB Weld.”
    …and therein begins the industry of cheap disposable 1 or 2 use engines…..

  13. when I was 16 I was given a 5HP Briggs & Stratton engine that ran but smoked. Tore it apart and it had digested a bolt or something and had a nice deep groove in the cylinder. I filled the gouge with JB weld, let it harden overnight, ran a hone through the cylinder, and put it back together. Wasn’t exactly the “right” way to do it but it didn’t smoke anymore and ran like a champ after that.

  14. About 9 years ago I repaired a John Deere A cylinder head that had cracked due to the owner not draining the radiator for the winter. Ground the crack out and JB welded it. It’s been running fine since then.

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