Engine assembly: Installing the cylinder headsNovember 29, 2018
In this portion of the engine assembly, we’ll look at cylinder heads and head installation. There are some words of caution here: If the engine has a roller camshaft (that requires considerable valve spring pressure), or has a set of stiffer than normal high-performance valve springs, you should exercise extreme caution if you decide to perform the assembly at home. We don’t recommend it. Springs under tension are extremely dangerous, and we’ll explain it further in another portion of the article. Aside from physically assembling the cylinder heads, installation is very, very straightforward. If you can tighten bolts and know how to operate a torque wrench, then it’s a piece of cake. Check it out.
Virtually all engine machine shops or cylinder head manufacturers will assemble the heads for you (as is the case with the engine build series cylinder heads). There’s good reason for this: They have the tooling and the expertise. But what follows is a look at how the assembly is accomplished.
When the machine shop rebuilds or blueprints your cylinder heads, the process of grinding the valves and grinding the seats will effectively sink the valves deeper into the cylinder head. What this does is change the installed height of the valve spring. Valve spring installed height is the distance from the base of the valve spring pocket on the cylinder head to the outer spring lip on the valve spring retainer.
Measurements to determine the valve spring’s installed height can be made a number of ways, but by far the easiest is with Crane Cams’ height micrometer. What it does is take the place of the valve spring in the cylinder head. The retainers and valve locks are installed, then the tool is tightened until it reaches installed height – basically, as far as it will go. Compare this dimension to the spring manufacturer’s specification.
How to adjust installed height
So how do you adjust installed height? Small adjustments are made by way of shims placed under the valve spring. Note that aluminum heads all require at least one hardened shim in order to prevent the spring from damaging the soft aluminum in the spring pocket. What happens is that the sharp, hard end of the spring erodes the softer aluminum cylinder head material. When you add shims, the installed height is reduced. If the installed height needs to be increased, there are two choices available: Increase the depth of the spring pocket or install valves with longer stems. Of the two, the use of valves with longer stems is much preferred. The reason is that cutting into the head to increase the spring pocket depth can weaken the head or inadvertently cut into a water jacket.
On a street-driven engine, valve stem seals are absolutely critical. Any oil that burns within the cylinder reduces engine power, fouls spark plugs and creates considerable tail pipe emissions, as we all know. To prevent oil from being drawn into the cylinders past the valve guides (as the piston goes down in the bore, it creates a vacuum), some form of valve stem seal is required.
Quality high-performance seals most often have a spring that holds the seal in place (by surrounding the seal). The sealing material is often Teflon® or another low-friction material. Some valve stem seals mandate that the valve guide OD (and sometimes the height) is machined to a specific size to accept the seal. Others are designed to install over the stock valve guide. In either case, the valve stem and the inside of the seal should be well lubricated. Many seals are supplied with a plastic installation tool that facilitates the installation. The seal must be carefully slid over the valve stem lock (keeper) grooves. The tool is placed over it and then lightly tapped in place over the guide with a small hammer.
Remember when we mentioned the dangers of installing valve springs? Here’s why: Today’s high-performance valve springs should be installed by an experienced machine shop. The reason for this is that the increased valve spring pressures found today mandate specialized tools (for example, a heavy-duty valve spring compressor, often air powered). Springs are under hundreds upon hundreds of pounds of pressure when compressed. If you make one miniscule error, the spring can physically launch off the cylinder head at what amounts to critically high speeds (some equate it to a bullet). That’s why a pro should install them.
Nonetheless, before the springs are installed, the head must be clean. Grit can enter the combustion chamber by way of the guides. Lubricate the valve stems with assembly lube and add the appropriate shims. As the spring is installed, it should only be compressed sufficiently so that you can install the valve stem locks (keepers). To keep the locks in place during the installation, it’s a good idea to coat them lightly with engine assembly lube or even a small amount of grease.
Installing the head gasket
Clean the cylinder block deck surface. Typically, we spray a small amount of brake cleaner on a lint-free shop towel and wipe the deck clean. Ensure the cylinder head dowels are in place on the deck surface. Following the head gasket manufacturer’s specifications, install the gasket. Some composition gaskets such as the Fel Pro Permatorque MLS shown in the accompanying photos do not require any special sealers and, as the name suggests, they do not require a hot re-torque. Some gaskets mandate a small bead of silicone be applied around the water ports in the deck surface. Other gaskets require sealers to function properly. In any case, the gasket can now be placed over the head dowels on the deck. Most gaskets are designed to either fit one way or with the part numbers facing up (toward you).
Installing the cylinder heads
Clean the cylinder head deck surface using the same process as used on the block deck surface. Rotate the engine on the engine stand so that the deck you’re working on is parallel to the floor. Carefully place the cylinder head on the deck, over the head gasket. Be sure the heads fully engage the alignment dowels and are flush with head gasket.
Before the cylinder head bolts are installed, be certain you have the right mix and length of fasteners. With the cylinder head installed, hand thread each head bolt into the block deck to determine the length is correct. In our case, we used ARP head bolts with hardened washers (which have an effect upon the installed length). Our big block example uses 16 head bolts in three different lengths per cylinder head.
Once the number of bolts and length is determined, you can install the fasteners. We always wipe the fasteners clean and follow the manufacturer’s installation instructions. Some engines (where the head bolt enters a water jacket) mandate a thread sealant on the bolts. Others such as our sample engine have blind holes in the deck. That means the bolts do not enter the water jacket and as a result, sealants are not required. Companies such as ARP provide a special assembly lube with their head bolts. Apply the assembly lube to the bolt threads as well as the area between the head bolt and the head bolt washer. You’ll note the head bolt washers are machined on the ID. The machined side faces the hex on the head bolt.
Torque the fasteners
Head bolts (or studs) should be torqued in three steps of equal value. They should also be torqued in the right sequence. The manufacturer of the engine you’re working on will definitely have a torque specification along with a sequence of which fasteners to torque in which order. Generally speaking, the sequence begins in the center of the engine and works outward.
What we try to do is to split the specified torque into three. For example (and this is only an example), if the engine manufacturer specifies the torque as 90 foot-pounds, we’d begin by setting the torque wrench at 30 foot-pounds and then go through the torque sequence. Next, we’d adjust the torque wrench to 60 foot-pounds and go through the torque sequence. Finally, we’d set the torque wrench to 90 foot-pounds and re-torque once more, following the sequence. Repeat the entire process on the second cylinder head and you’re done.
Install rocker arm stands
Conventional stud mount rocker arms are installed after the lifters are dropped into the lifter bore. Next, a pushrod is set in place and then the rocker arm can be installed on the rocker stud. It’s a simple process, and we’ll show more of it in the final segment.
A shaft rocker, such as the Jesel setup shown in our build, is a little different. It functions by way of a small shaft bolted to a stand. These stands are held in place by two torx-head capscrews along with a special link stand. First the link stand is set in place, followed by the actual rocker stand. Typically, the rocker stand for the intake differs from the one on the exhaust side. You have to be careful during the installation to ensure the right stand goes on the right rocker boss on the cylinder head.
On an engine such as the big block Chevrolet shown in the accompanying photos, two different length torx capscrews are used. You should use the longest bolt possible, but be sure to inspect the ports. In some cases, if a long capscrew is used, it will protrude through an intake port. If it does, switch to the shorter (supplied) torx fasteners. On cylinder heads where the capscrew (or the rocker arm stud) enters the intake port, you’ll have to use some form of thread sealant on the fastener threads.
Do not torque the stands in place at this time. You’ll have to complete the installation once the lifters and pushrods are installed. More in the next and final segment. In the meantime, cover the engine. You’ve almost reached a finished powerplant.
Here’s the valve spring assembly tool we mentioned in the text. It’s a height micrometer designed for use with (obviously) valve springs. Crane Cams manufactured this one. Essentially, it takes the place of the valve spring on the cylinder head as it is mocked up. Turning the micrometer (note the graduations) determines the installed height of the valve springs.
Take a close look at the pointer. See the blue piece with the little spring inside the valve spring? That is the valve stem seal. A seal is installed on each valve for a street-driven engine combination. Obviously, seals are installed as the head is being assembled.
Once the valve springs are compressed, the valve locks (or “keepers”) can be installed. Often they’re fussy to install. It’s easier if you add a little dab of grease to hold them in place as a valve spring compressor is being operated (although keep in mind that it’s advised to have a pro shop handle the head assembly when dealing with large valve spring pressures).
In many engines, you’ll discover there are different head bolt lengths. Be sure to sort and count them before the engine is assembled.
Companies such as ARP include fastener assembly lube with their head bolts. Apply a small amount to the fastener threads along with a small amount to the washer. The lube should be included on the side of the washer that comes in contact with the bolt head. FYI, a small amount of lube goes a long way here.
Head gasket installation is rather simple. In most cases, the gaskets can only be installed one way. In other situations, the gasket is installed with the lettering facing up. Before installation, clean the cylinder block deck surface with brake cleaner and a lint-free rag.
The cylinder head can be dropped on the dowels. Before you drop it in place, be sure to clean the head deck surface. We use a small amount of brake cleaner and a lint-free towel to wipe it clean. Here, the Brodix “Xtra O” heads are installed. Always double-check to make sure the heads are, in fact, dropped over the dowels.
Before torquing the cylinder head bolts, make it a practice to hand tighten each fastener to ensure it doesn’t bottom out. You’ll note here that we’ve hand tightened each fastener and checked the length on all of them. It takes some time to do this (taking into account an engine such as ours has 32 head bolts), but it’s better to be safe than sorry.
You’re ready to torque the head bolts in place. The text offers more info, but the idea here is to “sneak up” on the torque in three approximately equal steps. In addition, you should follow the factory sequence when torquing heads.
Here’s a photo of a Chevrolet shop (overhaul) manual showing the torque sequence for various engines. Essentially, it’s a practice of starting in the center and working your way out.
Once both cylinder heads are torqued in place, you can partially install the shaft rocker arm mounts (if the engine is so equipped). Here, we’re installing the Jesel rocker stand link to the rocker boss on the Brodix cylinder head.