A Spintron is a fixture which spins the valvetrain while measuring valve motion. This Spin
With advent of "spin machines" and dynamic analysis of valve motion, much more is known today about valvetrain technology than in years past. While a considerable amount of this technology has been advanced by the engineering staff at COMP Cams, there are some fundamental issues the Saturday Night engine builder (and racer) should come to recognize. If for no other reason than participants in these types of racing classes don't always follow the directions provided by experienced valvetrain and related component providers, it may be helpful to discuss some basic topics.
For whatever reason (improper valve spring pressure, incorrect match of cam lobe profile to spring combination, wrong camshaft break-in procedure, excessive engine speed, etc.), the inability of a valve to seat and remain seated upon initial closing contact is one concern. Separation of lifter and lobe at maximum lift is another.
In the first case, it's critical that a valve remain in contact with its seat the first time they come into contact, during a closing event. On the intake side, failure to accomplish this leads to a reduction in net inlet cylinder and combustion pressures, leading to lost power. This is a consequence aside from any mechanical damage that can occur, particularly to valve springs that already operate in a dynamically hostile environment. During improper exhaust valve closing, both volumetric efficiency and reduced combustion pressure (power again) stand to suffer. When lifter/lobe separation occurs over the nose of the camshaft lobe, the resulting "loft" can materially alter closing-side dynamics and valve timing, neither of which is good for power or parts longevity-particularly valve spring life.
In the application of a circle track engine, there are times when engines are subjected to over-speed conditions. Knowledgeable engine builders will tell you valve spring pressure (and life) diminish very rapidly after a condition of valve "bounce" occurs only once. In fact, the rpm at which valve control instability happens is reduced each time the condition is caused. What first occurred at 7,500 rpm, for example, may next occur at 7,300, then 7,000 and then even less.
Also critical is valve spring selection and installation. These seemingly-simple components are subjected to some of the most severe treatment in a racing engine that includes high operating temperatures and structural issues. Consequently, it's important to follow not only camshaft manufacturer recommendations regarding specific spring selection, but also making certain all recommended installation procedures are in compliance is equally vital to proper spring operation and longevity.
If you have any doubt an engine is or has been experiencing valve control stability problems, take the time to examine the participating components. Look for areas of abnormal wear on pushrod ends, rocker arm pushrod cups, interference marks on spring coils, "hammered" spring pockets and/or shims, damaged valve faces and seats, excessive guide wear-even interference between piston crowns and valve heads. Recheck seated and open valve spring pressures to make certain they're within recommended specifications. And, if any of these abnormalities are detected, identify the cause and take corrective steps. In this case, an ounce of prevention could help avoid pounds of damaged engine parts.
According to COMP Cams engineer Billy Godbold, "There are several fundamental valvetrain topics we feel the Sportsman racer should know about and understand that relate to our Cup engine research. These pertain to valvetrain mass and stiffness, valve spring weight, component material selection, the criticality of coil bind and the matching of system components.
"With respect to valvetrain mass and stiffness, most Sportsman racers don't own a gram weight scale. Not only should they have one, but be in the practice of weighing every component in the valvetrain. This includes valves, springs, retainers and locks. Actually, every gram that can be removed from these parts will allow faster lobe profiles, more engine speed and lower valve spring loads. All of these will reduce friction horsepower.