What Is Included in a Head Gasket Set and Do You Need New Head Bolts?

Most people never think about a head gasket until something goes badly wrong. The car starts running hot, there's a sweet smell from the exhaust, the oil on the dipstick looks like a coffee-and-milkshake, or the coolant keeps vanishing with no puddle on the drive to explain it. That's usually the moment "head gasket" gets typed into a search bar for the first time.

Then comes the confusion. You go to buy the part and find you're not buying a single gasket at all. You're buying a set, or possibly a much larger set, and somewhere in the small print there's a question about whether you also need new head bolts. Getting that second part wrong is one of the more expensive mistakes you can make on a home engine job, so it's worth understanding before you order anything.

What a head gasket set actually is

The head gasket itself is one part: a layered steel or composite seal that sits between the cylinder head and the engine block. Its job is to keep three things apart that all pass through that joint but should never mix. Combustion pressure, coolant, and oil all have their own galleries running through the block and head, and the gasket is the only thing separating them.

A head gasket set is different from that single item. When the head comes off, every other seal in the top half of the engine gets disturbed too. Rather than sell you eight or nine separate small gaskets, suppliers bundle them together as a kit. In the UK trade you'll sometimes see this called a VRS, short for Valve Regrind Set, which is an old-fashioned name from the days when heads were routinely removed to grind the valves.

So when you buy a head gasket set, you're really buying everything you'll need to strip the top of the engine and put it back together sealed.

What's inside a typical head gasket set

The exact contents vary by engine, but a standard set usually includes:

• The cylinder head gasket, which is the main event and the reason you're buying the kit.

• The rocker cover (or cam cover) gasket, so the top of the head seals properly once it's reassembled.

• Intake manifold gaskets, which have to be replaced whenever the manifold is unbolted.

• Exhaust manifold gaskets, for the same reason on the other side of the head.

• Valve stem oil seals, the small rubber seals that stop oil creeping down the valve guides into the combustion chamber.

• Assorted O-rings and small seals, such as camshaft seals or coolant transfer O-rings, depending on the design.

What you'll notice is missing from most sets: the head bolts. More on that shortly, because it's the part that trips people up.

Head gasket set vs full engine gasket set

There's a bigger kit worth knowing about. A full gasket set (also called an engine or overhaul gasket set) contains everything in the head set plus all the bottom-end seals. That means the sump gasket, the front and rear crankshaft oil seals, the oil pump gasket, and often the water pump gasket and core plugs.

You only need the full set if you're going deep, for example splitting the block or doing a full rebuild. For a straightforward head gasket replacement, the head set on its own is the right call, and it costs a good deal less.

Why the head gasket is the part that fails

It helps to understand why this one seal gives up more often than the rest. The head gasket lives in the worst neighbourhood in the engine. It's clamped between two large metal castings that heat up and cool down at slightly different rates, and it takes the full hammering of every combustion event, thousands of times a minute.

Overheating is the usual killer. If the engine cooks itself, the aluminium head can distort even slightly, and once the clamping load is uneven the gasket can no longer hold the seal. On some engines a warped head is the real root cause and the gasket is just the symptom, which is why any decent workshop will have the head skimmed and pressure-tested before fitting a new one. Bolting a fresh gasket onto a banana-shaped head is a fast route to doing the whole job twice.

The head bolt question: do you need new ones?

Here's the part that catches people out. For a lot of modern engines, the honest answer is yes, you need new head bolts, and reusing the old ones is a genuinely bad idea.

The reason comes down to how the bolts are designed. Older engines used conventional head bolts that clamp within their elastic range, meaning they stretch a little under load and spring back when loosened. Those can often be cleaned up and reused if they're within the length tolerance in the manual.

Most engines built in the last couple of decades use a different type: torque-to-yield bolts, sometimes called stretch bolts. These are deliberately tightened past their elastic limit during fitting, so they permanently stretch. You'll recognise the process by the tightening sequence in the manual, which reads something like "torque to 30 Nm, then turn 90 degrees, then another 90 degrees." That angle-tightening is the giveaway that the bolt is being stretched on purpose.

The point of the design is a very even, consistent clamping load across the head. The catch is that a stretched bolt has done its one job. It's already at its yield point, so if you reuse it and torque it again, it can stretch further, lose clamping force, or snap off in the block. None of those outcomes is one you want after you've already got the head off.

How to tell what your engine uses

You don't have to guess. A few reliable checks:

• Look at the tightening procedure in the workshop manual. Any angle-based step (degrees of rotation) almost always means stretch bolts that should be replaced.

• Inspect an old bolt. Torque-to-yield bolts often have a visibly waisted, narrower section along the shank where the stretching happens.

• Check the manufacturer's guidance for your specific engine code, not just the model. The same car can use different engines with different bolt types.

When in doubt, replace them. Head bolts are cheap compared with the labour of getting to them.

What actually happens if you reuse old stretch bolts

It's worth being blunt about the failure mode, because "you should replace them" doesn't always feel urgent when money's tight. Picture a set of tired stretch bolts holding down a brand-new gasket. The clamping load is now slightly uneven and lower than it should be. Under the heat and pressure of normal running, the gasket that had a fresh seal begins to weep. Within a few thousand miles you're back to losing coolant, or worse, you strip a thread or snap a bolt head trying to remove them again.

At that point you've paid twice for parts and twice for the labour, and possibly picked up a damaged block into the bargain. Set against that, a new set of bolts is one of the best-value items in the whole job.

What to check before you order

A quick checklist saves a lot of grief when the box arrives:

• Confirm the set matches your exact engine code, not just the make, model and year.

• Check whether head bolts are included or listed separately, and add them to the order if they're not in the kit.

• Decide honestly whether you need a head set or a full gasket set based on how far the strip-down goes.

• If the head is coming off because of overheating, budget for having it skimmed and checked, since a new gasket won't fix a warped head.

The bottom line

A head gasket set is really a top-end reseal kit, built around the head gasket but including the cover, manifold, and valve seals you'll disturb along the way. The single most common oversight isn't in the kit at all: it's the head bolts. If your engine uses torque-to-yield bolts, and a great many now do, fit new ones every time. They're a small line on the invoice that protects everything else you've just paid for.

Get those two decisions right, the correct set for your engine and fresh bolts where they're needed, and a head gasket job that sounds intimidating becomes a repair that stays fixed.

FAQs

Are head bolts included in a head gasket set?

Usually not. Most sets contain the gaskets and seals only, so check the listing and order bolts separately if you need them.

Can I reuse my old head bolts?

Only if your engine uses conventional bolts and they're within the length tolerance in the manual. Torque-to-yield (stretch) bolts should always be replaced.

How do I know if my engine has stretch bolts?

If the tightening procedure involves turning the bolt by a set number of degrees rather than just a torque figure, it uses stretch bolts that should be renewed.

What's the difference between a head gasket set and a full gasket set?

A head set covers the top of the engine. A full set adds the bottom-end seals like the sump and crankshaft seals, and is meant for deeper rebuilds.

Do I need to have the cylinder head skimmed as well?

If the failure was caused by overheating, yes. A distorted head stops a new gasket sealing, so it should be checked and skimmed flat before reassembly.