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Technical Direction On Rotating Assemblies

Experts explain why installing these matched, balanced and packaged components into a working race engine still requires a high degree of skill and experience.

By John F. Katz


While the rotating-assembly phenomenon has (somewhat) tamed the part-selection process, experts agree that actually assembling those parts into a working racing engine still requires a high level of skill and experience.

“People seem to believe that since it is a kit, that it takes zero engine building knowledge to assemble the bottom end,” noted Alan Davis of Eagle Specialty Products, Southaven, Mississippi. “We try to make it as easy as possible, but there are variables that involve the block and other components that are out of our control. There are also varying opinions regarding clearances—ring gap, bearing oil clearance, piston-to-cylinder, etc. So some engine-building knowledge is needed. We provide as much technical help as we can short of building the engine for the customer.”

“Probably the No. 1 area where customers get into trouble is thinking that they can do it themselves with only minimal experience,” agreed Mike Schropp of Livernois Motorsports, Dearborn Heights, Michigan. “With the cost of the components, as well the engine as a whole, this really is not the type of thing you want to try and guess your way through. You need to know what clearances to run, what to check, where to look for interference, etc. That’s not to say that DIY isn’t possible, but in order to do a really good job it’s imperative that you have help from someone in the know.”

“When ordering a balanced assembly,” added Jack McInnnis of PBM Performance Products, Louisville, Kentucky, “it is also very important to verify everything—pins, big ends, rings—as all will need to be final-prepped before assembly. And it’s critical to verify all the parts before starting to fit and assemble, to avoid problems in case returns are necessary.”

“Building an engine still takes knowledge and practice,” confirmed Kirk Peters of Lunati, Olive Branch, Mississippi, who noted that some of the most common questions Lunati receives from its customers concern torque and stretch in the rod bolts. “We tell them not to exceed the maximum torque to get the maximum stretch.”

According to Tom Lieb of Scat in Redondo Beach, California, people building strokers are most likely to call for technical help. “They have to have the proper base-circle camshaft, and they may have to take a little nip out of the block somewhere to clear the rod.”

The Scat catalog notes where machining is required, and Scat technicians are willing to provide guidance. But some customers want the impossible, and Lieb doesn’t hesitate to tell them so: “Like the guy trying to build a Windsor Ford with a 4 1/2-inch stroke. So I said, ‘Let’s take a look at what you are trying to do, and at what the issues are, and let’s do the math. Here’s your rod length, here’s your ring package. Here’s where you’d have to cut the counterweights to clear the pistons. And here are the issues with the camshaft. And I don’t think you really want to do this.”

“They read in the magazines about building big cubic inches out of a small block motor,” added James Beyer of Dakota Engine Builders in Jamestown, North Dakota, “and they don’t realize what a challenge it can be, getting all the parts to fit. Sometimes you have to clearance the rods and the block. But we tell them what to look for, and what to do; and if they don’t feel comfortable we tell them to bring it in and we’ll do it for them. I’d rather see it done right, and have a satisfied customer in the end.”

Clint Anderson of CNC-Motorsports in Brookings, South Dakota, tries to screen for customers “who are trying to achieve something that isn’t in their budget. There is so much stuff on the Internet about making this much horsepower, and the customer doesn’t necessarily understand the cost of the components they’d actually need to make that much horsepower and have the engine last over a long period of time.”

Conversely, Anderson continued, “If a customer only has x-amount of dollars to spend, we can mix and match brands to put together a custom kit that will provide the biggest bang for those bucks.” And customers seem to understand that they’re getting the best deal possible. “They grasp that we’re doing the legwork, and that we possess the knowledge to say, ‘For what you are trying to do, this is what it’s going to cost to buy parts that are going to last.’”

Technical Direction On Rotating Assemblies

Customers often mistakenly believe that installing a rotating assembly is a do-it-yourself project, when in fact, “This really is not the type of thing you want to try and guess your way through,” according to one supplier, echoing a familiar sentiment among industry experts.

Performance Racing Industry