Performance Head Build - Some Assembly Required

When It Comes to Performance, It's All in Your Heads

John Nelson Oct 10, 2006 0 Comment(s)


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 approximately five seconds with a lapping stick. In addition to verifying fit and seal, lapping will improve both by removing ultra-fine imperfections. It won't, however, cure something more serious, like a burnt valve. You'll know a burnt valve, says Alvarez, because it will actually be missing a small piece of material.

This is what a properly fitting valve/seat intersection should look like. The outline created in the dye should be of uniform width around the circumfrence of the seat and concentric with the valve guide. If anything looks wrong, a valve job may be in order; have it checked at your local machine shop.

Next on the agenda is establishing the valvespring installed height. If you know what cam you're using, and therefore which valvespring to use, you'll have the installed height spelled out for you. Check the sidebar for what to do otherwise.

When checking this spec with a height mic, be sure to use the retainer and locks you'll be using.

We're right on our 1.800-inch figure, but only because Alvarez uses a hardened steel spring locator on all Speed-O-Motive heads. Additional shims are added when needed to reach the proper height.

If you're using a head that doesn't have a pocket for a spring cup, Comp makes hardened steel spring seats that have their locating shoulder on the inside of the piece.

Speed-O-Motive uses high-quality, positive-lock valve seals when it builds its heads. If you're doing a lot of this kind of work, a seal-installing tool comes in handy. Powerhouse Products has one for a paltry $20.

Seals in place and installed height established, Alvarez proceeded to install the valves in our subject head. Each valve stem should get a dollop of assembly lube; spinning the valve as it's inserted into the head serves to distribute the lube along the valve stem and guide.

Before installing the springs, it's a good idea to check spring pressure, using the same retainer you'll be using in the final assembly. Our new Comp springs should show 121 pounds at 1.800 inches. We're showing 135 pounds, which is a bit high, but close to 10 percent of spec-and it'll come down with use.

The last step (but one) is to install the valvesprings. Alvarez does have an air-powered spring compressor to make the task easier, but the home builder will probably do this manually, as seen here. Powerhouse Products makes a reasonably priced version ($129). What's left? Alvarez gives each valve a whack with a plastic hammer to make sure the locks are seated, then performs a pressure test.

V-style head holder $36; Valve Spring Tray $30; Mini Spring Tester $79; Small Hole Gauge Set $69; Height Mic $63; 0- to 1-inch Outside Mic $19; Digital Caliper $50. All tools from Powerhouse Products except for the valve-lapping tool, which was $4 at the local auto-parts store.

Not too many home builders are willing-or able-to drop six-and-a-half bills on a full-fledged bench-top valvespring tester. Luckily, Powerhouse Products has a low-buck alternative. This mini spring tester is easy to use. Simply place a spring and the tester in a vice (as shown), then compress the spring to its installed height (or the height you're checking), as measured with calipers. The gauge will give you the spring pressure-in this case, 110 pounds. Nice. An inexpensive flange allows the tester to be used in a drill press.

Measuring valve-guide clearance is critical to building a solid set of heads. An outside mic for checking the valve stems is relatively inexpensive; an inside mic, for the guides, no so much. Again, here's a low-buck alternative.

Insert the proper tool from Powerhouse's Small Hole Gauge Set into a valve guide, tighten the knob until the end fits the guide, then remove the tool and measure the ball tip with your outside mic. Voila, you've got your valve-guide dimension.


Comp Cams
Memphis, TN 38118
Powerhouse Products
Memphis, TN 38118
West Covina, CA 91790