It is widely recognized that cast, machined metal parts tend to have "memory" created from internal stresses. In the presence of temperature changes, these stresses often cause dimensional and structural shifts. Racing engine builders know about this condition that can have a direct bearing on cylinder bore concentricity. In fact, we often spend extra time and funds to produce "round" cylinders in an attempt to produce bore dimensions equal to those that exist after an engine reaches operating temperature and cylinder pressures.
More specifically, cast and machined bores in a cylinder block are subjected to thermal and load distribution that add complexity to the goal of maintaining concentric bores in a running and highly stressed engine. Like it or not, there's some "Kentucky windage" built into the task of producing dimensionally correct cylinder bores that model those subjected to in-use heat.
We know the distribution of operating temperatures and combustion pressure are anything but uniform in the metal structure surrounding cylinders and the fact that three-dimensional growth of block material occuring in this proximity is unavoidable. So, we've contrived ways to pre-load blocks with honing plates; by heating the material or use of other methods intended to anticipate how a given block will experience bore distortion, once assembled with parts and running ... sometimes on the assumption that all bores will distort the same, which they do not.
None of this is to suggest such methods are not effective, because they have been and are. Rather, these comments go directly to the problem of devising improved ways to compensate for the "effective" distortion that is inescapable under the influence of operating conditions.
Enter Stephen Kuzara of Sheridan, Wyo.-based Millennium Products Corporation. Stephen's background is essentially two-sided. At 53, he has engineering training, 35 years as an engine builder/machinist and 16 years running his own machine shop. That's not an unworthy combination. During his time as a machinist when the use of torque plates came into common use, it appeared to him there must be other ways to produce concentric bores once put into operation.
In prior conversations he'd had with Smokey Yunick (who had tried the process of "hot honing" during the 1950s), Kuzara explored ways to circulate heated liquid through the cooling jacket of a cylinder block during finishing honing operations.
"Curiosity and frustration arose from chasing the final few tenths in the honing process," Kuzara says. "During the early '70s, I worked with a machinist friend who owned a CK-10. I began wondering how important those last few tenths were in the overall effort of achieving precision-machined blocks. I'd already observed how the stones would heat the bore surfaces and create dimensional changes, so it seemed logical some major changes would probably occur at engine operating temperatures."
In fact, Smokey had abandoned the process (although in the '70s he'd shared with this author the benefits he'd projected would occur), considering the way he'd tried the method was cumbersome, "messy," and "took too long."
Kuzara appears to have been more persistent. "My first setup was hooked up to our hot-water heater, with one hose running water into the block and another running out to the drain," he says. "The outlet hose had a pressure gauge and a valve to help monitor the pressure and control the flow. Water temperature during the first test I ran was at 180 degrees F. The distortion measured was significant enough that I quickly concluded the last few tenths I had been chasing 'cold' were lost in the greater distortion I was seeing 'hot,' which was several times that produced by torque plates."