Valve springs, valve clearance, bounce, float, and surge: A few helpful details

Valve springs, valve clearance, bounce, float, and surge: A few helpful details

By Archie Bosman: Valve springs have two primary tasks: first, to close the valve after the camshaft opens it and, second, to maintain proper valve clearance, also known as valve lash. Why valve clearance is required for solid tappets (lifters) Valve clearance, or tappet clearance, is the gap between the tip of the valve and the rocker arm when a solid lifter is positioned on the base circle of the camshaft. This clearance accommodates thermal expansion created by engine heat. Metal expansion rates differ between the block, heads, pushrods, valves, etc., and a gap commensurate with the collective expansion is set accordingly. Exhaust valve clearance is often greater than that of the intake valve as it runs hotter and, therefore, grows in length, reducing valve clearance. Unlike solid tappets, hydraulic systems operate with zero clearance. Inadequate clearance As the valve seat wears, the valve moves slightly upward in the cylinder head, reducing valve clearance. If clearance vanishes and the valve does not close fully, compression is lost. Furthermore, escaping hot combustion gasses burn the valve head. Similarly, when combustion occurs on race engines, heat and pressure can distort the valve head, cupping it and pushing the valve upwards through its seat, thus consuming some of its clearance. On overhead cam engines, which have fewer valve train components to absorb deflection during combustion, the effect of lost clearance can be evidenced by a little shock imprint on the camshaft’s base circle caused by the lifter. Excessive clearance In contrast, excessive clearance is detrimental to the entire valve train. As the bigger gap builds momentum, the rocker pounds the valve tip....
Developing Benetton’s F1 Active suspension system

Developing Benetton’s F1 Active suspension system

By Dave Hamer: I joined Benetton in 1988 when they decided to create an R&D department to support their Formula One active suspension ambitions. Both Lotus and Williams had already seized the moment, pushing well ahead with similar programs. Though Benetton was also running an Active test car, they employed a staff of only 80, considerably fewer than the other leading teams. The initial system was developed using various Citroen hydraulic parts, including accumulators and a pressure control valve. The hydraulic power was generated by a Sunstrand gear pump, similar to the high pressure oil pump of a central heating boiler, which Lotus also used at the time. However, these pumps were barely adequate for F1 use; operating at 2,000psi-plus, they required constant attention. The events that led to Benetton’s active suspension and the system’s major components The advent of aerodynamics and particularly ground-effect brought new challenges to suspension design. Ground-effect relied on the car running at a low consistent ride height and, as such, generated huge downforce and cornering power. Notably, spring rates had increased to 3,000lb/in., making the suspension almost solid. Yet due to tyre squash, the car’s ride height still changed with the car’s speed and its mechanical grip was poor. The solution came in the form of new technology known as Active suspension, which replaced the springs and dampers (mostly coil-over-shocks) and anti-roll bars with hydraulic actuators (rams) controlled by a computer. The system employed a pump to provide the pressurised fluid which was piped to a computer-driven valve (a moog servo valve) at each corner of the car. This either directed fluid to the...
How Kaase’s 2017 EMC-winning engine proved a point:

How Kaase’s 2017 EMC-winning engine proved a point:

This two-paragraph brief from engine builder Jon Kaase was uncovered during our research of the more extensive accompanying article on valve springs, valve clearance, bounce, float and surge.   Excessive valve spring pressure and its effect on lifters  By Alfie Bilk   Excessive valve spring pressure is detrimental to power production, as it creates more friction on the lifters. “On my last year’s Edsel EMC contender,” recalls Kaase,” I had single conical springs and noticed the intake adopting a rhythm and floating the valves about 6,000rpm.  So, I installed stronger springs and lost 15hp. I speculated the deficiency may involve the intake valves only, and I put the weak springs back on the exhaust, as those valves are smaller and lighter, and the engine picked up 7hp.”   Most of the power losses implicated by the use of stronger springs are caused by lifter friction. “The stronger the spring,” he explains, “the harder it is to raise the lifter. Even though you get some of it back when it’s closing, you are pushing it sideways against the lifter bore. This sideways force is called the pressure angle. A flat tappet is less threatened than a roller lifter. In the case of the roller lifter, you impose all kinds of pressure on the sides of the lifter bores. So the more spring pressure you apply the more power it consumes. Cup car teams learned these lessons and, as a matter of course, run light valves and light spring pressures.”   To read the about Kaase’s 2017 EMC winning engine click here.   Source Kaase Racing Engines, Inc. 735 West Winder...