What Does a Valve Float Do to the Hydraulic Lifters?

Hydraulic lifters can overfill with oil and cause engine problems.

Hydraulic lifters are devices designed to maintain a valve clearance of zero in an internal combustion engine. A valve float is a problem that occurs when the engine valvetrain poppet valves fail to stay in contact with the camshaft lobe during the valve closure phase. This can adversely affect hydraulic lifter function.

Compression Loss

If valve float occurs at high engine RPM (revolutions per minute), the hydraulic lifter pistons will raise to take up slack in the valvetrain. As engine speed decreases, the hydraulic lifters, now overfilled with oil, can prevent the valves from closing. This can result in cylinder compression loss, leading to engine backfire.

Engine Power Loss

Valve float results when the valve springs can't keep up with high engine RPM. These weakened springs may fail to enable the lifters to close the valves shut before the next engine cycle, resulting in a loss of both cylinder compression and engine power at high RPMs.

Damaged Engine Components

A valve that fails to close properly due to a weakened hydraulic lift function during engine cycles can strike a piston, resulting in possible damage to valves, pistons and other related components. Valve float can also cause valves to overheat and burn out, rendering them inoperable.

References

• Accelerated Motion: Cam Talk
• "How to Repair Your Car"; Paul Brand; 2006

Resources

• "The Complete Idiot's Guide to Auto Repair"; Vyvyan Lynn, et al.; 2007