Valve float is a common engine problem for vehicles that are used in auto racing. Symptoms of this mechanical malfunction can be alleviated if caught early in the inspection process. Valve float that is not properly repaired can cause extensive engine damage and cost car owners a lot of money in replacing part or all of the engine.
Valve float happens when an engine's springs can't maintain engine RPMs. These springs work to close valves that are opening and closing rapidly during acceleration and at high speeds where RPMs are typically as high as 5,000. If the valves are unable to close all the way before the next cycle begins it will cause the engine to misfire. Valve float can also cause hydraulic lifters supported by oil pressure to move up only slightly in attempting to close engine valves. As the engine slows down hydraulic lifters can remain too filled with oil. This will keep valves open and cause engine misfires.
Along with engine misfire, a vehicle experiencing valve float will also lose power at high speeds by failing to maintain adequate RPMs. The lack of timing caused by valves not properly closing is responsible for the drop in RPMs. The engine may regain compression at lower speeds which could cause a driver to think the problem was an isolated incident only to have it resurface when speeds reach higher levels.
Performance problems are not the only symptom of a valve float. This engine malfunction can actually cause bent valves which if left unchecked can collide with engine pistons. The result can be catastrophic damage to the engine's integral components resulting in engine shutdown. Valve float can also cause engine valves to run hot which can lead to burnout and failure of the part altogether. When this happens drivers will experience loss of engine power at all speeds. Driving the vehicle under these conditions is extremely hazardous and could ruin its engine.
