Modern MLS head gasket technology is lightyears better than old school paper and composite gaskets. However, proper installation and prep are key to making them bombproof! Here are some tips, myths, and general best practices for your next head gasket install.
Forget smartphones, super high definition televisions, and even that gizmo from Amazon that allows you to order a pizza just by talking to it. The best part about the latest advancements in technology is how it is now easier than ever to make big power in street and race engines.
These days horsepower freaks have a multitude of options when it comes to making power. But whether we are talking a supercharger, turbocharging, EFI, or even an old-school stroker kit—it all comes down to squeezing more air and fuel into the combustion chambers to create a bigger boom.
Of course, the more power you make, the more stress you create on the engine. In the old days, blown head gaskets were often issues when making big power. These days, it doesn’t have to be, but you still have to take the proper precautions. It all comes down to selecting the right components and preparing them properly. In this article we’ve got a few tips on things to do that will definitely help cut down significantly on the chances of a blown head gasket. Oh, we’ll also dispel a few myths that can actually do more harm than good, too.
Composite vs MLS
MLS gaskets have been available now for several years and are no longer just for expensive, high-end race engines. MLS (which stands for Multi-Layer Steel) gaskets are a step up from standard-issue composite gaskets thanks to their construction. Composite gaskets are made with steel fire rings for each cylinder surrounded by some other material. In the event the cylinder head lifts even a bit, combustion gases can escape past the steel fire ring and burn the gasket in the brief moment before the head is pulled back into place.
MLS gaskets are constructed from three or more layers of steel. The outer layers are embossed around the combustion chambers as well as the water jacket and oil gallery holes leading between the block and cylinder heads. With this configuration, if the cylinder head lifts the embossments act as springs to help maintain proper sealing to keep the combustion gasses where they belong.
MLS gaskets also do a superior job sealing between disparate materials. These days, aftermarket aluminum cylinder heads are becoming a lot more popular as the prices for a quality head are coming down. But when you first fire up an engine with a cast-iron block and aluminum heads, the heads absorb heat faster than the cast-iron block, causing it to expand more quickly. An MLS gasket is better at handling that difference in expansion rates than a typical composite gasket. In the event you get into pre-ignition or detonation, the more robust MLS gasket is also better at withstanding the tremendous spike in pressure those events create.
A blown head gasket is almost always blamed on—you guessed it—the head gasket. But if you haven’t laid the proper foundation by properly machining the decks of both the block and cylinder heads, every head gasket will fail. Both the deck of the block and the cylinder heads should be machined so that they are flat and parallel to the centerline of the crankshaft to within a couple thousandths of an inch. The decks must also have an extremely smooth surface. Most modern machine shops can accomplish this with ease, but it is important not to install MLS gasket on a pitted, worn, or roughly machined deck.
You can’t achieve that with hand tools no matter how careful you are. It doesn’t matter how good you are as an engine builder, unless you are trying to drive some jalopy out of the junkyard or get the demolition derby car through one more night of carnage, it’s always a good idea to have a machine shop clean up the decks for both new engines and rebuilds. In the long run, it will always be worth it.
Fathers taking the time to teach their sons and daughters how to work on cars is a great thing. What’s not a great thing is when they accidentally pass along bad, or outdated, info.
A perfect example is copper head gasket spray. In the old days racers and engine builders would try to get overmatched head gaskets to handle extra power by coating them with a copper-based spray. This would fill in surface irregularities in the deck of either the block or cylinder heads and also help dissipate heat from hot spots (often between the side-by-side exhaust ports on small block Chevys).
But that old trick is now bad info which should be left in the past. Spraying an aftermarket coating on a quality MLS gasket can actually hurt its performance. For example, JE’s Pro Seal MLS gaskets are all constructed from stainless steel and given a multi-layer surface coating that includes a “primer” to help it stick to the stainless gasket, a high-strength Viton layer to mold to minor surface imperfections on the head or block, and finally a top-layer silicon coating which is especially good at sealing the coolant and oil passages moving from the block to the heads. Modern surface coatings on quality MLS gaskets do a better job than a hand sprayed copper “paint” ever could, so save your money and leave that stuff on the parts store shelf. All that needs to be done is use a to properly clean all metal surfaces before the gasket is laid down.
No matter how good the head gasket, it is still extremely dependent on proper clamping load from the head fasteners to help it work properly. Achieving a good, uniform clamping load across the gasket is dependent on three factors: fastener hardware, consistent torque on the fasteners, and the pattern used to tighten fasteners.
Typically, the OEM’s use torque-to-yield head bolts to clamp the cylinder heads to the block. Torque-to-yield bolts are one-time use only. So once you pull them off, throw them away. Usually, these bolts can be identified because they will have a flat gray surface coating, but if you aren’t sure, always play it safe and buy new head bolts.
You can buy replacement torque-to-yield head bolts relatively cheap, but we would advise against it. Instead, invest in a set of quality fasteners made by aftermarket manufacturers such as ARP. Not only are these fasteners less prone to failure, they also allow higher clamping loads and are reusable through multiple engine rebuilds.
When buying new fasteners, you can choose between head bolts and head studs. Most high-performance engine builders use head studs whenever possible because they can provide a more consistent clamping load. This is because the head stud is threaded into the block without any resistance. Then the head is installed and clamped in place with nuts on the head studs. This allows the studs to be place almost into pure tension rather than torsion.
Head bolts, on the other hand, must be spun into the block as torque is applied. This means the bolts can be twisted as the last bit of torque is applied, making the overall clamping pressure sometimes less consistent than it could be. Head bolts are, however, sometimes necessary because they make it much easier to pull a set of heads while still in the car because once the bolts are removed the cylinder heads can be lifted straight off. This often isn’t possible with head studs because the heads have to be slid out and up until they clear the studs, and the car’s fenders or other parts can get in the way. So before purchasing new fasteners, plan ahead and determine if you might be pulling the heads with the engine still in the car.
When installing the head fasteners, it is critical that they never be installed dry. This allows friction between the threads of the fastener and the block to create too much resistance, which can cause clamping loads to vary wildly. Instead, some sort of lubricant should always be used. ARP has created a thread-lubricant they call Ultra-Torque we’ve found works very well. Other engine builders swear by old-school “High Pressure Lube,” which comes from a variety of manufacturers. What shouldn’t be used as a lubricant is motor oil, which is too thin to provide good consistency.
Different lubricants provide different levels of “lubricity,” which is a fancy way of saying how slick they are. It is important to know exactly what lubricant you are using because it will affect the force applied with your torque wrench. A torque wrench measures resistance to a twisting force. Meanwhile, proper loading by the fasteners requires them to be in a specific amount of tension in a straight line down the length of the bolt or stud. Essentially, they are tightened to the point that the bolt or stud stretches a few thousandths of an inch, putting it into tension. The fastener reacts to being in tension by trying to pull back to its original length, pulling the cylinder head tighter to the block.
Manufacturers like ARP provide proper torque specs for bolts using different lubricants. It is important that you follow the exact specs for the specific lubricant you are using because they account for the lubricity, or slipperiness, of the lubricant. For example, if you want to properly load the head gasket while lubricating the head bolt threads with Ultra-Torque you may need to set your torque wrench to 70 ft/lbs, but if you are using motor oil which does not do as good a job at lubricating the threads, your torque wrench should be set higher. Make sure you always use the correct torque setting for both the fastener and lubricant you are using.
Finally, the order in which you torque the head fasteners in also important. There are lots of diagrams and charts on the internet showing the correct order to tighten the head bolts for practically any cylinder head, but once you understand the concept you won’t need them. Always start with the center most bolt or head stud, then work your way out in the spiral pattern. That helps spread the loading over the head gasket evenly to give it the most strength possible.
Last, but certainly not least, always take a few moments to prepare both the block and heads before beginning assembly. Even with a new engine build, use a thread chaser to make sure all the threads in the bolt holes are clean, straight, and free of burrs. If you don’t have a set of thread chasers, you can use a thread tap if you are very careful. This will help make sure you get proper loading of the head fasteners without anything to screw up the torque readings.
And while you are at it, take a moment to chamfer any sharp edges created by the machining processes used to create the component. Sharp edges not only create weak points but can also keep the cylinder head from sitting perfectly flat. You can use sandpaper or a deburring tool to cut down any burrs and sharp edges. It only takes a few minutes to do, but it can be the difference between a great engine build and one that causes endless frustration.