VALVE SPRINGS

The valve springs’ job is to shut the valves after the camshaft has opened them, and keep them shut until the camshaft opens them again. In theory it is straightforward, but there is a bit of science involved when choosing the springs to match the camshaft.

On a camshaft with high lift the opening and closing ramps on the lobes are usually quite steep and aggressive. As you can imagine, when the engine’s revving at 7000 rpm the force at which the valve hits the seat as it closes is quite hard, and it is likely to want to bounce back off the seat a little.This is where uprated valve springs matched to the camshaft are needed, as they will keep the valve shut and eliminate this problem.

Also the valve springs have to be matched for height to avoid becoming coil-bound at full valve lift. A higher lift cam will compress the spring more than a normal lift cam, so the valve spring will need to accommodate this. A valve spring should always have 40 thou’ clearance between the coils when at full lift.

Double valve springs are also available for high-performance engines and work in the same way as single springs.The main benefit of double springs is they offer more strength to keep the valve closed, and it is not always possible to achieve this strength with a single spring.

The second, inner spring is shorter than the outer spring.This means the valve is easier to open because there is less resistance at first, but when it closes it has the force of both springs pressing against it.This also helps keep the valve shut in engines with aggressive camshaft designs.

“DOUBLE VALVE SPRINGS OFFER MORE STRENGTH TO KEEP THE VALVE CLOSED”