By on April 28, 2011

When your 1980 Porsche 924 craps out minutes after the start of its first race and you’re in rural Texas, parts might be a little hard to find. You won’t get far with a blown head gasket and big ol’ notches burned in the head itself. But, damn, the clock keeps ticking! The Moose Knuckles team called every junkyard within 500 miles, but nobody had any 924 (or Audi 100) cylinder heads. In fact, nobody had ever heard of them furrin thangs.

The Moose Knuckles were able to find a head gasket a few hours’ drive away, but they came up with exactly bupkis on the head. But then one of the guys remembered the fine print on the JB Weld package: Repairs Engine Blocks. Block, head, what’s the difference?

Picking up some JB Weld and JB Kwik, the Moose Knucks got right to work. Sure, combustion-chamber temperatures get higher than the JB Weld-rated 500 degrees F, but we’ve seen such repairs work in the past… on cast-iron heads. What will happen with an aluminum head?

Fill in the holes with that magical gray stuff, sand it down, and slap the head back on the engine. Take the car on the track. Return behind the tow truck. Repeat. Endlessly.

Because the track exit at MSR comes before the transponder loop, and the Moose Knuckles’ Porsche never managed a full lap under its own power, all those laps that ended on the hook didn’t count. Official race results counted the car as a DNS. On the bright side, the Moose Knuckles took home the I Got Screwed award.

Just so you don’t think JB Weld repairs always fail at LeMons races, here’s a JB-patched E30 oil pan from the same race. The car wiped out, bottoming the pan and cracking the hell out of it. Thanks to a generous application of metal-filled epoxy, the car finished the race.

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40 Comments on “Field Expedient Engineering: JB Weld Porsche Cylinder Head Repair...”

  • avatar

    My best ever JB Weld repair was on a now-ex girlfriend’s Corona. She told me it seemed to have a coolant leak so I popped the hood to find the entire brass tank at the top of the radiator was cracking and disintegrating. We couldn’t afford a new radiator so I slathered a 1/4″ thick layer across the entire tank and overlapped it onto the edge of the core. Once it was done there was essentially a tank made of JB weld with the filler neck sticking up out of it. It was still holding pressure fine she junked it due to a grenaded transmission a year later.

  • avatar
    Educator(of teachers)Dan

    My favorite JB Weld story is the farmer who  wrote the company to tell them it was “better than duct tape and baleing wire.”

  • avatar

    How many sets of headbolts did they end up using… or (god forbid) did they use the same ones over and over?

  • avatar

    They could also have looked for an AMC Gremlin head, as some of them had the same engine. The 2.SLOW in the MK3, MK4 and new Jetta is supposed to be from the same engine family, so it might be interesting to see if the head off a current one fits the 924’s block.

    • 0 avatar


      The 2.0 used in the 924/Audi 100 is the precursor to the 5-cylinder used in later Audi’s and shares the same bellhousing pattern with them.

      The 924 motor shares nothing with the VW 4-cylinder engines. Bellhousing, bore spacing, etc are all different. So unless the MK3/MK4 Jetta are using defunct Audi derived 4-cylinders (Audi’s 4-cylinders since then have been VW-based as they focused on the 5’s, 6’s and 8’s)

      The engine design itself was done by Mercedes for Audi, which was then used by Porsche in VW’s defunct project which became the 924. VW decided to make the Scirocco instead.

      Both the 924 and the Scirocco used A1 Rabbit parts. The Scirocco used more of them. The 924 used them more inventively and the 924 used Super Beetle rear suspension. The 944 dressed the Rabbit/Super Beetle parts in cast aluminum to hide their rather plain beginnings.

      Little known fact: The Audi V6 and V8 use the same bellhousing pattern as the 5-cylinder and the 4-cylinder 924/Gremlin/Pacer/100.

  • avatar

    So years ago when a young man working in Boulder CO a friend stopped by driving from Idaho to Kansas City in a 1970 Chevy Suburban panel truck loaded with hydroponic equipment in the back. Just when he hit town the column shifter snapped off at the base of the shifter, it was a 3spd manual. We bought about eight tubes of JB Weld and built up gradually a big blob-collar around the break and test drove it around town, seemed to work. next morning he took off for KC, since this was pre-cell phones I didn’t know what happened for several days. Turns out the shifter snapped on the third shift so he drove all the way to KC in second gear at 40 mph.  never saw a cop once.

  • avatar

    Epoxy inside the combustion chamber RIGHT BY THE EXHAUST VALVE failed to hold up?  Imagine that!

    Years ago my brother tried to fix the broken generator brushes in his JAWA motorcycle with JB weld.  Didn’t work because the stuff does not conduct electricity.  I wonder if there is any real validity to metal-bearing epoxy like JB weld or is this just a gimmick?

  • avatar

    What you guys don’t have someone on staff who can weld aluminum with 1 hand tied behind his back  and grade the specific alloy out of the possible thousands, simply by licking it? 

    F*&^ing amateurs. ;D

    • 0 avatar

      No heli-arc @ Lemons?
      I’m a bit surprised.
      Even our local bang em up stock car track has a welding truck at all the races.

    • 0 avatar


      Or, drill and tap several small holes along the crack and thread in plugs. Grind smooth. One million pre-1935 engines are currently running around with just this fix.

    • 0 avatar

      Cast aluminum is a tough material to weld, also even if you have the right alloy of aluminum for welding the contamination caused by years of immersion in oil, fuel and other grime can often render a decent weld near impossible.

  • avatar

    Fixed our garage door opener with JBWeld and a bunch of bolts laid in it for strength.  A roller broke and the door fell down shearing the follower right in half.  JBWeld held up for 10 years, till I replaced the opener with a newer one. JBWeld gets substantially weaker as the temperature goes up above 300 or so…becomes soft and pliable.

  • avatar

    “JBWeld gets substantially weaker as the temperature goes up above 300 or so…becomes soft and pliable.”
    Me, too.

  • avatar

    I used JB Weld to seal a crack in the lower unit of my 90HP Yamaha outboard boat engine. Saltwater corrosion had set in and a tiny hairline grew to about 1/8″ wide by 6″ long around the outer gear casing. The inner case was still sealed so I just JB Welded the outer casing. Despite the vibration it held for over 8 months, considering it was under water in a saltwater environment that is pretty remarkable to me. It was still going strong when I hit a rock at around 30 mph which bent the prop shaft rendering the whole lower unit a total loss.

  • avatar

    Not knowing much about 924s I’ll make some (perhaps obvious) observations:

    1) There are no recessed combustion chambers in the head, it seems flat as Kansas. I have never seen that before.

    2) It is not a cross-flow head like one might expect on a performance engine.

    3) The head casting seems to have a lot of pores for a car from a manufacturer noted for its engineering prowess, or is that where the gasket failed around the fire ring?

    • 0 avatar

      It’s not a particularly high-performance design because it’s an Audi motor.

    • 0 avatar

      “1) There are no recessed combustion chambers in the head, it seems flat as Kansas. I have never seen that before.”

      It’s called a Heron Head. The combustion chamber is in the dished-out piston top (which can be seen on one of the other pics). Simplifies manufacturing of the head. It’s been used in various motors over the years. The one that first springs to mind is the Jaguar V-12.

      • 0 avatar

        Also the big feature of Moto Morini motorcycles during the ’70’s and ’80’s.

      • 0 avatar

        Only the early Jag V12s. The later HSE versions had a combustion chamber machined into the head after the 1979-80 oil crisis in the wake of the hostage taking of the US Embassy staff in Tehran made fuel economy a priority. I believe that the hot tip for Jaguar 12s is to use a later block (which are 6.0L as opposed to 5.3L on the early engines) with early heads.

        One of my dream projects is to built a Locost Se7en using a XJS or XJ12 as a donor car. The idea of putting a V12 in a Seven is just too silly to not try. Hot rodders have been using the bolt up Jag IRS since the 60s, and the entire front suspension and steering also mounts on a subframe. There are Locosts with LS and LT V8s, and some with inline sixes, so a V12 isn’t that much of a stretch, pun intended. I’d be sure to somehow integrate the original Jaguar cowl so it’d have a VIN plate and I could register it as a Jaguar. Murilee tells me that the LeMons powers that be might even let me race it for the We Don’t Roll On Shabbas racing team.

      • 0 avatar

        My turbo diesel Peugeot had the same setup

    • 0 avatar

      It is a cross-flow head.

      Combustion chamber is in the pistons.

      Incorrect type of antifreeze tends to lead to issues like this in German cars. Coupled with the need to run water only (many folks don’t use distilled water)

      Porsche hamstrung the 924 with piss-poor port design because it could have been faster than the base 911 at the time, which would be verboten.

      So it isn’t a performance engine in the classic sense (just like an A1 GTi engine isn’t either) but it could have been better than it was.

      The folks on the are spread throughout the country and probably could have come up with a head for them.

      Next time, get a big propane torch and some aluma-weld (aluminum solder essentially) Brush the area to be repaired with a stainless wire brush/wheel. Heat the head, flow the solder, cool and then sand smooth.

      For something that big, might have to build an ersatz oven out of bricks to get it warm enough. A propane BBQ set on high for a couple of hours might work. Just use protection and move quickly.

  • avatar

    I noticed from the photos they were using JB-KWIK. It’s only rated to 300 degrees, not 500 like the regular product.

  • avatar

    I fixed a leaking coolant flange on my Ranger with JB Stick. It has held up for 2 years now. I thought I was going to have to replace it a long time ago. It was only supposed to be a temporary repair, because the part was on Back Order from Ford, and I didn’t have the time. I never ended up ordering the part. I think if it starts leaking, I’m just going to reseal it with some more JB stick.

  • avatar
    Andy D

    528e gas tanks are prone to rusting out around the filler neck, top and sides. I have used JB Weld 2part and stick to patch up the tanks. Only 1 failure so far.

  • avatar

    I’m surprised that nobody brings along a few sticks of Alumaloly, Steelaloy or Castaloy ( Supposedly you can “weld” the stuff with a simple propane torch (though you might want to use a turbo torch or MAPP gas to get the base metal hot enough to take the weld).

    FWIW, I used a metal epoxy to fix a part on my embroidery machine. The part serves a few functions including being a reference point when adjusting needle depth as well as keeping the non moving parts of the rotary hook in place. On one of my four sewing heads, that part had somehow gotten bent by a previous owner. I stupidly tried to straighten it without heating it up first and it snapped in two. I put the epoxy on the two broken ends and then pretty much covered the thing with the stuff. After it cured, I used some sandpaper to remove the excess. It’s worked fine for a couple of years at least (it’s not really a stressed part, though).

  • avatar

    JB Weld is a factory-approved repair for Saab 900 2.1L heads. They tend to suffer severe erosion around the water passages, then leak like sieves. But I don’t think it works when the JB Weld is right into the combustion chamber! Great effort though.

  • avatar

    “Sure, combustion-chamber temperatures get higher than the JB Weld-rated 500 degrees F”

    Not really relevant, since the heat transfer is such that typical cylinder head wall temps are well under 400 F.

  • avatar

    You can’t defeat physics, but you can always try.

  • avatar

    I seem to recall problems on Honda V6 blocks. Something about porous castings. I believe the fix from Honda was to repair using JB Weld.
    Probably just an urban myth.

  • avatar

    My best JB weld fix was on a dodge shadow I was using as a rallycross car. The thermostat had failed, but the top bolt for the housing was seized so tightly it may as well have been welded into the head. It sheared off the head, and after a good oil soaking and filing the remainder flat, that sheared off… then more penetrant, application of heat, unintended application of heat (small fire, no biggie), I broke the first extractor. Managed to get that out with a chisel, and promptly broke a second extractor off, amazing since the metal behind the threads was paper thin at that point.

    In hindsight after the first extractor broke I could have just tapped the hole I drilled in the bolt, but there’s a reason it’s called hindsight.

    I broke out the dremel and cut the corner off the ‘water box’ on the head and STILL had to use a chisel to break chunks of bolt off the remaining threads. I coated the replacement bolt with vaseline and carefully laid it in place, built a dam of cardboard around the missing chunk of head, and filled it up with JB weld. It held fine for about two years before the whole thing popped off, presumably due to expansion/contraction.

    the final fix was to deepen the hole enough to get 5-6 threads and using a longer bolt with spacers to adjust the final depth to use all those threads. As far as I know, that’s still working fine, sold the car a year back to a guy who said he would use it as a circle track car.

    That car was unkillable. Just a bottom of the line ’91 “America” 2.2l 5 speed. By the end of my time with it, it had been stripped to the point that the instrument cluster was zip-tied to the firewall along with the other controls, AC removed (seized anyways), made it 80 miles home with a giant chunk of water jacket seal missing out of the head gasket (stopped every 10 miles to bleed the gasses out of the radiator), bounced around fields and tracks hard enough to bend all 4 factory steel wheels (tire rack’s snow tire package steelies are much thicker/heavier replacements), suffered a decent fuel-leak inspired engine fire which managed to only melt the edges of a few connectors, somehow ingest a bolt, rock, or chunk of something hard enough to scar up the surface of #4 piston and do no other damage, and survive a backwards drop out of my driveway and down a 45 degree incline hard enough to dig a 6″ chunk of asphalt up with the tailpipe with only a slight tweaking of the rear quarter panels at the sail panel (ok, and wrapping the tailpipe around the axle). And there’s still so much more… like angling into a dip on the rallycross course wrong, and digging the front crossmember into the dirt so hard it forced it through the steering column boot and sprayed me with it head to toe. *no damage*, which is fortunate ’cause I drove it 90 miles home that evening…

  • avatar

    I’ve seen J-B weld used to repair VW vanagon crank case. Heat really wasn’t an issue-except when the owner would use his Coleman catalytic heater to warm the engine up in the winter so it would start.

  • avatar
    John Horner

    JB Weld to patch up an oil pan? Sure.

    JB Weld to fix a head …. never had a chance. JB Weld can’t take the mechanical stresses or temperature. Didn’t anyone at the track have a TIG welding set up? That could have worked.

    • 0 avatar

      Probably because a good portable TIG welder costs 3 times as much as any of the cars do. As I posted above, welding an aluminum head in the field is an iffy proposition. First it has to be of an alloy that can be welded, second the contamination from years of fuel, oil, coolant and other grime creates such porosity that you can’t get much of a bead at all, or you have a weld fails almost immediately. But it would certainly be worth a try if the head was scrap anyway.

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