The Most Tortured Part In An Engine
851,428
Published 2023-01-07
A modern head gasket is an intricate hybrid mechanical seal engineered to fill the space between a reciprocating engine’s head and block.
SEALING ENGINE LUBRICANT
A head gasket must seal the passages that carry engine oil between the block and the head. Engine oil can vary dramatically in viscosity and temperature, ranging from the extreme lows of frigid ambient temperature to as high as 135°C or 275°F.
SEALING ENGINE COOLANT
Similar to engine oil, on most water-cooled engines a head gasket must also seal the passages that carry engine coolant between the head and the block. When compared to engine oil, engine coolant has a relatively consistent viscosity, with a lower maximum temperature of around 120°C or about 250°F, with normal operation seldom reaching above 140°C or 220°F. Much like with engine oils, the materials that seal engine coolant, on top of thermal cycling and movement, must deal with the corrosive properties of engine coolant.
SEALING COMBUSTIONS GASSES
Sealing combustion gasses are, by far, the most brutal and critical requirement of a head-gasket. A head gasket forms part of the combustion chamber and If this seal is compromised, the affected cylinder will lose the ability to produce a normal combustion sequence. Depending on the nature of this failure, the cylinder may also consume or cross contaminant other engine fluids.
STABILITY
A head-gasket must be deformable enough to maintain a seal between the imperfections of the head and block surfaces. In addition to these forces, head-gaskets have to function under the dynamics and extreme mechanical stresses of combustion pressure. The head bolts that fasten the head to the block are also typically not symmetrically spaced, creating an unevenly distributed clamping force across the gasket. With each of these bolts exerting a force of up to 4,500kg or about 10,000 lbs. Beyond these expectations, they must also be durable and capable of lasting across a significant portion of the engine’s life with little to no maintenance.
FIRST HEAD GASKETS
With the introduction of the internal combustion engines in the 1860s, almost every type of elastic material ever used within steam engines was experimented to seal combustion. As the internal combustion engine transitioned from its experimental early days to a mass produced power plant, copper would become a popular material for these early head gaskets. Their relative motion would create inconsistencies in the clamping force along the gasket’s surface. This was such a problem, that In the early days of motorsport head-gasket failure was the most common reason for race cars to not finish a race.
NEW GASKET TECHNOLOGY
As the automotive industry began to flourish in the 1920s and 30s, less costly, mass-production friendly head-gasket designs were explored. One durable yet relatively inexpensive option was the steel shim head-gasket. Embossments are stamped, raised regions on critical sealing areas off a gasket that created a smaller contact point.
COMPOSITE GASKET
The beater-add process offered a new lower cost gasket material option that would lead to manufacturers eventually introducing the composite head-gasket in the late 1940s. Metal beads, called fire rings, are created within the gasket’s metal structure to seal the combustion chamber and protect the elastomer material from overheating. The non-metallic surface of the gasket is then impregnated with a silicon based agent to seal any pores and prevent the gasket from swelling when it comes in contact with liquids. Some designs may even incorporate seal elements made from a high temperature, chemical-resistant fluorocarbon based elastomer material called Viton.
MLS HEAD GASKET
In 1970, Japanese gasket maker Ishikawa was issued the first patent for a revolutionary, new type of head-gasket, called the multi-layer steel or MLS head gasket. They effectively combine all of the benefits of previous gasket technologies into an extremely durable and adaptable component. The outer surfaces of the gasket are typically coated with a thin, fluorocarbon based Viton layer, in targeted areas, to aid in surface sealing.
OTHER GASKETS TECHNOLOGIES
The elastomeric head-gasket is an example of a cost-reduction focused design. These gaskets use a single steel shim with a beaded coating of an elastomeric material such as silicone or Viton for fluid sealing. On the opposite end of the performance spectrum, are modern solid copper head-gaskets. These groves carry a stainless steel O-ring that when combined with a solid-copper head-gasket capable of sealing in some of the highest combustion pressures found within reciprocating engines.
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All Comments (21)
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I have a 1976 Triumph Spitfire 1500 that the previous owner had ground the head down to increase the compression. It was so high that I couldn't get rid of the pinging with the highest gasoline available to me. I bought two stock head gaskets and I found some company that made me a copper one. I sandwiched the copper gasket in between the two stock ones ( I sprayed a copper sealer on them first) and bolted it down tight. That was around 25 years ago and it still purrs like a kitten.
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Even as a former Subaru owner I never thought about head gaskets as being that high stress of an item, you've really out a whole new perspective onto things with this video for me
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Many years ago a co-worker asked me to take a look at the engine of a boat he bought cheap. The engine did not run and upon disassembly, I showed him the head gasket was completely worn out. Due to the cost of a gasket for an outboard motor, he wanted assurance that it was the only problem. He did not want to spend money on a new gasket to only find out the motor had other issues so I took some common gasket material and made a temp head gasket and reassembled the engine. It started and ran nicely. He asked how long the temp gasket would work and I had no idea. It was the same type of material used for water pumps. I said, maybe a minute, maybe an hour. I really did not know. Just buy a proper gasket now that you know the engine is good. Well... he did not listen. That weekend he went to the lake and took off with his boat across to the farthest point when suddenly, the gasket failed. With no oars, he and his friends hand paddled the boat back. I laugh so hard when he told me what happened. 🤣🤣😁
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A minute of silence to those cars owners that got a call from their mechanic and ended up here to find out what a head gasket is
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I work in healthcare and know next to nothing about engineering. I’m blown away by the complexities of mechanical engineering that are never learned by the average person who depends upon engineered machines in all aspects of life. Truly a joy to learn about these subjects.
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I loved head gaskets as a mechanic. Good flat rate hours, easy to do, virtually no come backs, and a steady supply of them coming in. Especially older composite head gaskets with an MLS replacement.
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I have replaced several head gaskets in my short time working with combustion engines, and I never stopped to actually truly appreciate how well engineered these parts have to be in order to survive hundreds of thousands of miles on the road. Thank you for this video! This has really given me a new perspective on a part of an engine that most people don't even know exists!
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In 2005/2006 we were trying to build the 1st 1000whp e36 328 (m52 engine) The toughest/most aggravating part of the build was getting the headgasket to seal under high boost. Around 17psi the gasket would blow out in between cylinders. One reason why we went with the 2.8L m52 instead of the 3.2L s52 from the m3, m52 has a bore of 84mm and s52 is 86.4mm. Those extra mm's made all the difference. Even with the extra material we still o-ringed the block n head. That was the trick that put us for ahead of the competition and helped us have the world's 1st 1000whp m52. Also 1st in the 9s while still having full interior, heated seats and ac.Havnt been back to the track ever since we got kicked out and told we need a parachute lol. 16 years later and only like 2 others have made that much power. Truly were miles ahead of the competition.
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Engineering is really really fascinating, the small things we take for granted in everyday life that came from decades of research and trial and error, fantastic content!
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Dude this channel is like a modern day "Modern Marvels" no BS just easy to understand and straight to the point explanations for very complex and complicated concepts. This channel has answered certain engineering, mechanica,l and material-science questions I've had for years answered within 20 minutes.
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This was very interesting! Great timing I'm rebuilding an engine for my truck at this very moment.
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I work in heavy truck parts sales, and all of our parts are BIG, including head gaskets. We have a regular customer who constantly questioned the price of absolutely everything he'd try to buy from us. One day he came in looking for a head gasket for a Paccar MX-13, of course he was quite shocked at the $350+ price tag, but I told him we don't carry aftermarket options. So I went to go get the part, and when I came back, sure as hell he asked me "what does this part do anyway?" I was actually too stunned to speak...not because he didn't know what it does but because he was questioning me on price WITHOUT knowing what it does. I had to educate the guy on its function but to this day I was genuinely stunned that the owner of this truck, did not know what the part was, why it was important, and why it's so expensive. Don't friggin question me on the price of a part when you don't even know why it is probably the most important part of your truck you DUMB WALNUT. This video reminded me of that incident, tis a great vid.
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There's a reason YouTube is still relevant today and it's because creators like you. Another great video!
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Imagine someone asking that question to this guy at a bar and then he drops this
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I love how something so simple can become a fascinating video and something that I don't think I've ever really seen anyone else on YouTube address like this. Can't wait to start sharing this with friends.
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Blown head gasket is still the most common engine failure you hear from people to this day, at least here. Unless you really mistreat your engine it's fairly unusual for any of the mechanical parts to fail. I've only had one engine fail really badly (i melted 3 of the 4 pistons), because I kept running it for over 100,000km with a blown turbo seal - it would lose oil pressure at idle, but as soon as you revved over 1000rpm the warning disappeared. Eventually it gave way completely, sucked all the oil through the intake, and I ran it dry at 200km/h until it cooked itself to death. The oil light never came on and coolant temp. was normal, I only noticed something was wrong because I tried accelerating and it was not responding. I stopped as soon as possible (less than 1km) but by that time when I opened the hood the turbo was glowing orange. After refilling with oil I still managed to turn it back on and drive 20km to the mechanic, surrounded by a cloud of oil. Absolute tank that engine.
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EXCELLENT VIDEO! Me, ASE Certified Master Engine machinist for over 30 years. I have been working in the engine rebuilding industry for 55 years. Had my own shop for 20 which included a Comec wet surface grinder capable of accuracy of .001 per 12" of length which is what we used to surface both the heads and blocks. Back when I opened my engine shop in 1978, we saw a lot of Honda 1200 and Chevy Vega engines with blown head gaskets. The Honda was all aluminum while the Vega was Aluminum block and cast-iron head. Both used the "open deck" type of block. Both were composition gaskets "squishing" about .007-.008 when torqued. My thoughts were that the cylinders were "moving", and the gasket was not adequately being compressed on the cylinders. My solution was after machining the gasket surface of the block flat, I then went around the outer edge of the block and machined an additional .001-.0015. That resulted in the cylinders "standing proud" .001 compared to the edge of the block for a tighter clamp on the fire ring. This really helped the durability of the gaskets. But they still needed retorquing which in the case of the Honda meant removal of the rocker arm assembly since it sat over the head bolts, UGH! About this same time a LARGE gasket company (FP) announced their no-retorque head gaskets! We were jumping for joy thinking of all the time they would save and started installing them on our engines right away. Within WEEKS we started seeing problems! These engines started spitting out head gaskets some in as few as a couple of thousand miles! The VWs in particular would come back with actual pieces of the gasket hanging out from the edges of the head! We stopped using them and went back to OE type gaskets and the problems ended. The company asked me to send them back so I sent 1 of each, Honda, Toyota and VW. They called me and said they would warranty the gaskets. I said that was OK but did they want me to send them the REST of the failed gaskets we had? "How many more do you have?". I told them 32, SILENCE. Then he said "let me talk to someone". Another voice on the phone "Is there a major airport near you?" yes "A couple of reps are going to fly to your shop and see if we can tell what's happening". The next day the VP and head of Tech arrived at my shop. After examining my machines and procedures they could find nothing I was doing wrong and said they felt it was the area WATER that was the cause!. I was stunned but before I could open my mouth he said "BUT, we are prepared to offer to pay you parts & LABOR for all the failed gaskets PROVIDED you sign a release form and will make NO further claims against us. It was a LARGE CHECK so I took the offer. They must have sold a LOT of those gaskets, we continued to see failures of them that others had installed for YEARS after that!
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Oil pressure should have been up to 5,5 bar, not 50. The convertion from imperial went wrong
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The most highly stressed component in a race car is the nut that holds the steering wheel!
