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I often hear of people who mix up valve lash (clearance) inspection/adjustment with a valve job. The latter actually refers to refurbishment of valve seats & faces and measurement & inspection of all related valve train components; valve clearance checks are simply routine maintenance.

The job of a valve seat is more complex than most people realize, but I will explain the basics to help you understand the importance this part of your engine plays in the performance of the whole package.

The seat provides the required seal to ensure optimum compression. It also acts a a heat sink to cool the valve. The various angles and widths of the valve and seat are critical with respect to maximum flow potential. So it should now be obvious that a deficiency in this area can cause all kinds of problems.

The most important component of a good valve job is concentricity. This will both ensure optimum seal and promote a longer life span for both surfaces.

In order to obtain the most concentric seats with perfect repeatability, an engine builder must utilize modern methods and equipment such as SERDI. The old stones and singular cutters such as Neway just cannot produce the desired results of the live pilot, blade type machines. Also note that "lapping" is what a dog does in its water bowl, and has no place in a performance engine, as it just hides a poor valve job! (It is also the best way to destroy a titanium valve found in most modern engines).

Consider that with a SERDI valve job, all valve heights can be equallized, which not only standardizes spring seat pressures, but alows the builder to verify combustion chambers are the same volume (an often overlooked source of power in multi-cylinder engines).

In closing, be sure to find out what method your engine builder utilizes, as now you can make an informed decision.