By Titus Bloom:
Research of racing parts invariably includes discussions with race engine builders and manufacturers. During their course, jewels of information can emerge, as was the case when we were developing a story following JE’s announcement of their advanced Pro Series head gaskets. Sometimes the gems are universally known sometimes not – still, these recent comments on surface flatness by Dick Boyer, designer of the latest engine blocks from World Products, seem noteworthy.
“The profilometer is useful,” says Boyer, “but measuring the scratch depth in a deck surface is usually of less consequence than wave finish. What would be the point of having a beautifully smooth surface with a potentially threatening wave depth of 0.002in or 0.003in? Some builders probably put too much emphasis on profilometer readings and maybe not enough on surface flatness.”
How do you check wave finish?
“We lay a granite plate with 300-grit sandpaper on the deck of the block and stroke it five times front to rear—you’ll see the high spots, you’ll see the wave, which we measure with an indicator. We aim to limit variations in wave depth to 0.001in. It’s easy to control the prolifometer readings; it’s less easy to control the wave. I’ve seen waves measuring 0.002in which introduce sealing problems.”
Boyer on torque-to-yield fasteners
“When installed, torque-to-yield fasteners, which are common on road-going vehicles, are stretched to their maximum limit and discarded after use.
If the bolts are not stretched to their full extent when the engine reaches normal operating temperature, they stretch a little more and the gasket gets loose. Torque-to-yield fasteners are not common in racing engines.”