Find out what goes into building a set of top-quality, reliable cylinder heads.
Careful measurement and attention to detail are key.
If something goes wrong, too much!
In one important respect, cylinder heads are like many other parts of our beloved Chevy powerplants. Done right, they provide miles of high-performance enjoyment; done wrong, they can bring the ride to a screeching halt. In this case, we're not talking about cylinder head performance per se, at least not when it comes to flow numbers and compression ratios. What head makes the most power has been covered elsewhere. What we're talking about here is the basic but complex act of cylinder head assembly. Basic because they sit atop our engines and do the will of the camshaft in regulating the internal combustion cycle; complex in that there's a lot of moving parts in a typical cylinder head, meaning there's room for error. And who wants that kind of misery?
Looking to understand what it takes to properly assemble a set of cylinder heads from bare castings to ready-to-install lungs, we went in search of professional help. Our friends at Speed-O-Motive take cylinder head assembly seriously-so seriously, in fact, that they build up all the heads they use from bare castings. The man who builds these heads for S-O-M is one Oscar Alvarez, who's been doing this kind of thing for neigh on a decade. We spent a good half-day with Alvarez, trying to glean all we could about the proper way to assemble a set of cylinder heads.
There's no way we can boil down our sensei's teachings into a few words, but we did ask Alvarez to start us off with a few tips:
Oscar's Top Three Tips
1. Check for correct spring pressure.
2. You must check the head surface.
3. Use top-quality parts.
After our time with Alvarez, we'd have to add this: there may be no substitute for experience, but making careful measurements, paying attention to detail, and learning from the experience of others can get you a long way toward a reliable set of cylinder heads.
Alvarez actually gave us a fourth tip-in fact, he feels so strongly about it that he gave it first. "People have to check the valve/piston clearance," he declared. "It's the most common mistake I see." Unfortunately, that process is a bit outside the scope of this article. On the other hand, what's the point in building a solid set of heads, only to have valves banging against pistons the first time you fire her up? With this in mind, we'll get to work on an article on checking valve/piston clearance. For now, here's a look at what it takes to build a bulletproof set of cylinder heads.
Whether you're assembling an all-new cylinder head combo or refreshing a tired set of lungs, much of the info we've given you here applies. Reusing a set of valvesprings, however, may require a few extra steps. First and foremost, the springs should be cleaned and checked for visual damage. When it comes to checking spring pressure and installed height, Alvarez left no doubt that the best way to make these measurements is to follow the manufacturer's specs for the cam you're using. Don't know what 'stick is in there? Get ready for some shimming. "If a spring pressure is very low," Alvarez told us, "you can shim it and bring the pressure up." As for installed height, you'll need to use your height mic on each valve, find the tallest installed height, then shim the rest to match.
If you're working with used heads, it's critical that they be cleaned and crack-tested bef
The first part of checking valve-guide clearance is to mic the valve stems. If the stem me
Step two is checking valve-guide clearance. Alvarez began by checking the guides themselve
On the other hand, if the guides are on the tight side (i.e., the measure is smaller than
On the other hand, there's also the seat-of-the-pants method for checking valve-guide clea
With all our valves and valve guides good to go, it was time to check out the valve seats
CHECKING FOR COIL BIND
It's imperative to make sure that the valvesprings you're using can handle the cam you're using. If the spring binds, or becomes "stacked," you can end up with a lunched cam. So, while you're compressing springs, here are two ways to check for coil bind:
1.800 Installed spring height
-0.500 maximum valve lift
=1.300 Compressed spring height
With the spring at its compressed height, you should have a minimum of 0.060 inch clearance between the coils, measured with a feeler gauge.
You can also compress the spring until it is completely compressed ("solid height"), make a measurement, and subtract this figure from the compressed spring height. For example:
1.300 Compressed spring height
-1.200 Solid height
=0.100 Compressed spring clearance
And as it turns out, 0.100 inch is the minimum clearance you should have. Whatever method you use, this is an easy way to ensure valvetrain longevity.
Shims come in 0.015-, 0.030-, and 0.060-inch sizes. If you're 0.005 short, that's OK; if you're 0.010 short, use a 0.015 shim to come in at 0.005 over.
Taking 0.006 inch off the head surface decreases the chamber volume by 1cc.
If you're not having a valve job done, each valve must go back in its original spot.
Use a spring locator instead of a .060-inch shim. it'll positively locate the spring, and its extra durability will protect the head surface.
When the layout dye is dry, each valve was placed against its seat and twisted for approxi
This is what a properly fitting valve/seat intersection should look like. The outline crea
Next on the agenda is establishing the valvespring installed height. If you know what cam
When checking this spec with a height mic, be sure to use the retainer and locks you'll be
We're right on our 1.800-inch figure, but only because Alvarez uses a hardened steel sprin
If you're using a head that doesn't have a pocket for a spring cup, Comp makes hardened st
Speed-O-Motive uses high-quality, positive-lock valve seals when it builds its heads. If y
Seals in place and installed height established, Alvarez proceeded to install the valves i
Before installing the springs, it's a good idea to check spring pressure, using the same r
The last step (but one) is to install the valvesprings. Alvarez does have an air-powered s
FOR THE DIYER V-style head holder $36; Valve Spring Tray $30; Mini Spring Tester $79; Smal
UNDER PRESSURE Not too many home builders are willing-or able-to drop six-and-a-half bills
WE LIKE MIC Measuring valve-guide clearance is critical to building a solid set of heads.
Insert the proper tool from Powerhouse's Small Hole Gauge Set into a valve guide, tighten