VALVE LIFTER PROBLEMS
Lifter Preload
The lifter preload must be checked and adjusted.
Some engines may require the use of longer pushrods or valve lash caps. Several length pushrods are available to accommodate adjustment. If the preload is not set correctly the circlip may come out of the lifter or the valve may be held off the seat.
Valve Bounce and Pump Up.
When valve springs have insufficient pressure an engine with a solid lifter cam will valve bounce. This causes an enormous heat build up in the spring and in seconds it will start to burn the oil. The heat build up causes rapid deterioration of the spring. This results in valve bounce at even lower RPM. The damage caused by valve bounce or float is often evident in valve ends being mushroomed, valve seats and valves being deeply grooved, especially inlet valves. Excessive valve bounce often leads to catastrophic engine failure.
Engines with hydraulic lifters have a built in governor as the lifter will "pump up" when the valve springs loose control. This holds the valve off the seat for a short time which prevents the cylinder building up compression until the lifter has settled and the valve can return to the seat correctly.
Anti Pump Up Lifters
Anti pump up lifters are designed to be used in applications where there is a chance the lifters will pump up. They have a slightly faster bleed down rate than the standard lifters. The most important feature of anti pump up lifters is the heavy duty circlips used to prevent the lifter from dismantling when the piston pumps up against the circlip. These lifters should be used in racing classes where the valve springs are restricted or in applications where the customer does not want to spend money on heavy springs. If an engine with suspect valve springs and standard lifters is allowed to rev to the point of lifter pump up the circlip in the lifters will be dislodged, there is nothing to retain the piston, it will pump up and could dislodge the pushrod. If the valve springs are suspect then the valve train should be adjusted to have 0.005" tappet clearance this will prevent the lifter from holding the valve off the seat.
When dismantling an engine make sure that the lifter bores are not damaged by hitting the edges of the holes when removing the lifters.
Lifter Bores should be carefully deburred to ensure there are no sharp edges when re assembling the engine. Burrs can prevent the lifter from rotating which will result in premature wear of the lifter and cam lobe.
High oil pressure can aggravate the pumping up of the lifters.
Scuffing of Lifters
The face of a used lifter should have a high polish. If the face has a dull mottled appearance it is due to microscopic tearing of the surface due to a lubrication problem. Check the face of the lifter for radius by placing another lifter on its side across the face. The centre of the lifter should be around 0.0015” -0.0020" higher in the centre.