Valve engine problem Brisbane -

PICKED UP / SEIZED

Valve guides and valve stems operate under very harsh conditions. There is a fine line between oil control and the lubrication requirements of the valve stem and valve guide. Due to the extreme temperature exhaust valves operate at it is more common for an exhaust guide seizure than an inlet guide seizure. With minimal lubrication that exists at valve guides and valve stems it is crucial to run the correct valve /guide clearance.. Things to check when valves seize are: oil feed to valve gear, operating temperature, valve guide clearance , valve stem finish and carbon build up at port side of stem. If valves are bead blasted during a valve grind and the valve stems were not protected or re- polished the roughened finish from bead blasting could contribute to seizure. Extra friction caused from the course finish will generate more heat which will contribute to seizure due to the minimum lubrication available at the stem area. Dry assembly of valve to guide is also a common cause. Unlike most other high friction points in an engine valve guides are almost completely sealed from lubrication. Quite often the valve stem will momentary seize in the guide and free itself. This condition usually ends up with a flogged out guide as the stem now has welded material stuck to it that rapidly wears out the guide. As engines start to burn a little oil, carbon starts to build up on the lower half of the valve stem. If no carbon relief was made at the lower end of the guide this carbon can make the valve start to stick or eventually seize in the guide. The early symptoms of this problem is an inconsistent engine miss at idle accompanied by a loud inconsistent tappet noise. If the engine is driven without this problem rectified a burnt out valve will normally be the result. This condition does not allow good valve to seat contact so as to dissipate the heat from the valve head. Valves can seize in a guide as a result of a bent valve. This usually happens when a valve clips a piston during an over rev and suffers a minor bend at the head and stem of the valve. Incorrect camshaft timing can also be responsible for the valve damage. The bent valve is forced into the guide by valve spring tension but jams partially open. This can cause further valve and piston damage as the valve stops in a position for further contact with the piston. As the engine continues to rotate the valve eventually breaks out the lower half of the guide. Continued use of the engine will eventually result in a major breakage of the valve and piston. Disclaimer Agreement : Every care has been taken in writing this information and procedures, but no responsibility can be excepted for errors, omissions or misuse of this information and procedures. The information available on this site is for your instruction only and cannot be copied for sale, © copyright 2001 UMR Engines