Head gaskets often get blamed for engine problems. But that’s often an unfair accusation. The real issues maybe with the installation, including the torque and pattern of cylinder head fasteners and selecting the right gasket thickness for the application.
These factors work together to ensure a long-lasting, high-performance diesel cylinder head gasket. Gasket thickness is particularly important for a number of reasons.
First, the basics. Gasket thickness is the distance between the cylinder head and engine block when the head is installed according to instructions.
It’s not the installation thickness that counts. The compressed thickness when the gasket is installed makes all the difference. You can’t really measure the compressed thickness of a gasket when it’s installed. You have to look at the specifications for your application and find a gasket that meets those specs. You may have to use a depth micrometer to measure the OEM gasket or the piston clearance of a modified engine or resurfaced block.
Every head gasket product listing and packaging should display the compressed thickness when properly installed.
If you’re doing extensive mods or giving an engine with lots of miles a little TLC, you may wind up needing a head gasket of a different thickness than the OEM option. The stock head gaskets in most light truck diesel engines will handle 1.800 to 2.200 PSI of combustion pressure. But a tune can push those pressures up to 2,700 PSI or even higher. That’s where a performance gasket is necessary to contain those pressures.
Head gaskets contain the pressure in the cylinders, sealing the gap between the cylinder head and the engine block. One common sign of a minor head gasket leak is coolant blowing out of the reservoir under heavy loads, like towing.
Beyond the basics of keeping the rapidly expanding gases and flowing oil and coolant in their proper place, head gasket thickness plays a role in the compression ratio.
Changing head gasket thickness is another lever to pull in dialing in the compression ratio for best performance. The compression ratio describes the relationship between the maximum and minimum cylinder volume. Air and fuel mix and detonate ignite in the cylinder, and the resulting pressure pushes down on the piston. The thickness of the gasket, which separates the block from the cylinder head, plays a role in the compression ratio by altering the volume of the cylinder.
Creating more pressure means the piston pushes harder and faster, making more horsepower and torque. Increasing the compression ratio means the engine produces more power. Turning up the turbo boost, increasing fuel rail pressure, and other tuning tricks increase the compression ratio. Other factors like valve and ignition timing also play a role in engine performance.
In forced-air induction or turbocharged diesels, the cylinder is under pressure at all times and can reach up to 200% or more of the cylinder pressure at sea level.
Increasing compression ratio is a good-news/bad-news situation. The good news is, you’ll get more power out of your engine. The bad news is a higher compression ratio can break stock parts, including your head gasket.
Also, resurfacing the engine block deck to address wear and tear or corrosion may require a thicker gasket to maintain stock clearances. When the block is resurfaced, a few thousandths of an inch of metal are machined away to ensure a consistent, smooth surface. The pistons will produce more power because they are closer to the top surface of the block. The volume of each cylinder is reduced, lowering the volumetric efficiency and increasing the compression ratio.
Some manufacturers recommend using the thinnest gasket possible to increase the compression ratio by lowering the cylinder volume.
Depending on how much of the surface is removed, you may need a thicker head gasket to preserve the piston-to-deck clearance to ensure the pistons don’t hit the head under a heavy pull. The cylinder heads can also be machined to provide a smooth, level surface. If you’re machining the head on a high-performance build, consider a fire-ring gasket kit to ensure the gasket can withstand the pressure.
Keep in mind the thickness will also affect the gasket’s ability to seal the combustion chamber and oil and coolant passages.
Diesel trucks have been around for decades, so there is a confusing variety of engine variations and head gasket designs. Many aftermarket sources are available with a gasket thickness chart for most applications.
Check your engine’s specifications and the gasket’s applications. Engine specs can change over the years, so it’s not safe to say a V8 Cummins Gasket will fit any model or year of Cummins. Don’t guess. Do your homework to find the right gasket. But also, it helps to know the rules before you can break them.
For example, the GM 6.6L Duramax has two base designs based on model year and three thickness grades. There are also options for engines that have been overbored, deck milled, or both.
Mid-2000s Ford Powerstroke 6.0L engines are notorious for head gasket problems, even in stock configuration. Aftermarket gaskets with extra layers seal better and have a much longer service life than the OEM options.
Some engine builders recommend using the thinnest gasket possible. But that may not be the right course of action in every case.
In some specific applications, thicker gaskets make sense. Any time you modify a diesel engine for more power, you should step up to a performance gasket. You’ll have less chance of coolant and oil leaks, loss of combustion pressure, and ultimately gasket failure.
As these modifications will likely include machining head and block deck surfaces for flatness and a smooth finish, a thicker gasket should be part of the plan.
If you’re replacing the gasket without machining or upgrading, a thicker gasket could help fill the gaps in the rougher head and deck surfaces.
Thick gaskets can fill in the gaps with less-than-perfect heads. Less clamping force is needed because of the give or less compression, which might seal better. A thinner gasket that requires more clamping force could be more likely to leak in this situation.
However, a thicker gasket may require more frequent retorquing to maintain an adequate clamping force on the head. You’ll want to check the manufacturer’s cylinder head fastener specs and check the piston-to-head clearance.
The thicker gasket has more surface area exposed to the pressure, which pushes it out of its rightful spot between the cylinder head and the block or between the cylinders. The extra surface area increases permeation or leakage through the gasket material.
Also, using a much thicker gasket can alter valve train geometry, and not in a good way.
As we discussed above, a thinner gasket can add a compression ratio and horsepower. Use a thinner gasket where it makes sense, given the other aspects of your engine work. A thinner gasket could result in a few additional horsepower and a smoother, quieter engine.
The gasket specs will vary based on your goals. If you’re building a 2,000-hp dragstrip monster, you’ll likely have different needs than someone looking for better mpg while towing their boat.
The answer may be different if you’re trying to eke out another 100,000 miles from a truck that works for a living.
This is not a place for guessing or estimating. If you’re not sure how to figure out the right gasket thickness, consult with an expert. Using the wrong head gasket thickness could result in piston-to-valve contact, leading to catastrophic engine failure. Look at gasket manufacturers’ and OEM’s gasket thickness chart to see what’s available for your application.
Have your mechanic check the piston protrusion and piston-to-valve clearance to determine the minimum safe fit. Or you can use a depth micrometer to check where the pistons are in relation to the engine deck surface.
Specialty gaskets like copper and MLS gaskets help improve the seal for high-boost applications. Rubber-coated copper gaskets tend to seal better than bare copper options.
Head gaskets often get blamed for failures when the fault lies in other aspects of the build. Head gasket torque is a critical element, and getting it wrong will sap your truck’s performance and durability. Some OEM bolts are known to stretch, resulting in loss of clamping force and head gasket leakage.
The condition of the mating surfaces on the head and engine deck is critical. Don’t overlook the importance of flatness in the surfaces for the best performing seal. Surface finish is critical as well; the smoother, the better. Some engines are notorious for corrosion incursions and other poor design choices that doom a truck to serious engine problems.
All of these elements have to work together to wind up with a head gasket that delivers the longevity and reliability that you need for your diesel truck.
If you’re working on a high-performance build and understand the importance of gasket thickness, consider upgrading to high-performance head studs from TrackTech Fasteners®. As you complete the build, the TrackTech head studs provide the right amount of clamping force to keep the head and head gasket in place on the engine block. These studs are engineered for high-performance applications that exceed the OEM requirements.
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