Identification of Valve Problems

Identification of Valve Problems Points : identification of valve problems, local leakage, leaking valves stem seals, valve breakage, stuck valve, valve float, Worn valve guides and stems. A worm valve guide or stem will allow the valve to rock or tip sideways in the cylinder head. Excess clearance between the stem and guide will result, as shown in the figure below.

This can cause a tapping noise oil consumption, spark plug fouling, or valve stem breakage. To check for worm valve guides remove the valve cover Use a large screwdriver to pry sideways on the valve stem. If the valve wiggles in its guides, remove the cylinder head for guide repairs. Local Leakage Local leakage past the seat, owing to distortion or incorrect re-facing or grinding in will have a similar affect. Major leakage past the scat caused by deposits of carbon breaking away and lodging on the seating is another contributory factor block or cylinder-head distortion cannot be ruled out. This is often caused be incorrect tightening of cylinder head bolts or by partial obstruction of the cooling water passage usually as a result of deposits at these points. Leaking Valves Stem Seals Leaking valves stem seals will let oil drain into the clearance between the valve stem and guide Oil will be pulled into the intake or exhaust port, and burned. The engine will emit blue smoke especially after initial starting or upon deceleration. Valve Breakage Valve breakage may be caused by valve stem fatigue or broken or week valve spring allowing the piston to hit the valve head. When the head of a valve breaks off, it usually causes severs damage to the piston, cylinder wall, and combustion chamber. Stuck Valve A stuck valve results when the valve stem rusts, corrodes and locks in the valve guide. This can happen when the engine sits is storage for an extended period. Valve Float Valve float is a condition in which weakened valve springs, hydraulic lifter problems, or excess engine running causes the valves to remain partially open. This problem usually occurs at higher engine speeds. The engine may begin o miss, pop or backfire as the valve float.

Weak valve springs are the result of prolonged use. The springs loose some of their tension. The springs become too weak to close the valves properly.

A broken valve spring will let the valve hand partially open. Excess valve-to-rocker clearance may cause valve train clatter (light tapping noise). Popping or backfiring can also result.