The problem is you can only detect damage to the lifter since you check lash with the lifter on the base circle and any damage to the lobe won't show up. You should also check for metal shavings from the damaged cam in the oil and bearings. A broken axle or failed needle bearings in a roller lifter isn't as big of a deal, but the problem lifter should be replaced or rebuilt immediately and the lifter bore checked for wear to avoid further engine damage.

Finally, lash can also be used sometimes as a tuning tool for your engine. Dorton says you can usually tighten or loosen your lash safely by 0.004. Tightening the lash will cause the cam to engage the valve more quickly, which will result in the valve opening sooner, lifting higher, and closing later. Essentially, it makes the cam act larger. Loosening the lash does the opposite, making the cam act smaller. Running tests with different lash settings on a dyno is a good way to see if your engine could use more or less cam.

But Dorton also gave us one more trick that you might want to consider if you are qualifying poorly and in danger of missing the field. Although he doesn't recommend doing this regularly, he says opening up the lash an extra 0.006 will often pick up qualifying times on a typical half-mile track by around 0.2-second. This is because the first few degrees of the opening and closing ramps on a cam lobe are designed to gently lift the valve off the seat and drop it back into place again without damaging the valvetrain. Opening up the lash by six thousandths effectively removes this part of the cam lobe from the process and makes the valve action much more violent. That delayed opening helps create more compression and power, but it's also very hard on the valvetrain.

Dorton says he's done it when a team needed to pick up a couple of tenths in qualifying in order to make the race or have a shot at the pole, but only when the track would allow him to re-adjust the valves before the race started. "You can't leave it like that," he explains, "because there's no way it will finish the race without damaging something."

Now grab that feeler gauge and get to work.

Automotive Specialists
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