July - Aug. 1999 Lane Racing And Rodding Article By Jim Kaekel, Jr.
When a broken valve drops down into a running engine's cylinder, the block, cylinder head or rotating assembly components are often damaged beyond repair. Valve train failures can be very costly, but most can be avoided through careful valve train component selection.
In a race engine, radical cam profiles subject valves, pushrods, lifters, rocker arms, valve keepers, retainers and valve springs to tremendous loads. The extremely quick opening and closing action will find the weak link in a valve train in no time. That's why camshaft manufacturers all list recommended components for use with each one of their camshafts. These components are specifically matched in terms of material strength to withstand all the stresses that a camshaft can dish out. Many cam grinders even offer complete component kits which include all the recommended parts in one package. The "kit box" approach will provide the best insurance against valve train failure.
Let's narrow our field of vision for a moment here and take a look at some common valve failures and what causes them.
Keeper Groove Failure
is quite common and is usually fatal to a race engine. The grooves are highly stressed, particularly if valve train geometry is incorrect, valve spring pressure is excessive, or if spring heights are not properly set. Once the grooves fail, there is nothing to stop the valve from dropping straight down into the cylinder.
Channeling occurs when small, pie-shaped pieces break off the valve face. The cause is most often excessive temperatures created on the valve face by "peening" or deposits which have built up on the valve seat.
Warping and Burning both result from extreme heat caused by poor air/fuel ratios, improper spark plug heat range, retarded ignition timing, vacuum leaks, or inadequate cooling.
Off-Square Seating occurs when the valve face and guide are not aligned. The valve stem is subjected to extreme side loading and even though valve stems have a degree of flexibility, they will eventually break.
Many of these failures can be avoided by stepping up to a premium race quality valve and then carefully assembling everything. Valves are available in a variety of stout materials including stainless steel and titanium. Of course, the better the valves, the "pricier" they're going to be. It's strictly a pay now - or pay later situation, however.
The threat of keeper and retainer failure should be real enough to also spend the extra bucks for high quality pieces. In fact, the price difference between standard locks and retainers is nearly negligible when the consequences of potential failure are mixed into the equation.
Many racers have no choice and must use stock - or stock appearing - valve train components because of class restrictions. What about the racers who purchase a high RPM camshaft and then choose to stick to the stock valve train because of a restricted budget or lack of experience? Stock valve train pieces will begin to fail when the engine exceeds 6,000 RPM and they will soon find that they could have bought a full set of premium roller rocker arms, stainless steel valves, chrome moly retainers, hardened keepers, chrome moly pushrods and double valve springs for the price of the cylinder head or block that was "trashed" because they chose to save a few bucks.
In short, it is best to follow the camshaft manufacturer's recommendations concerning matched valve train components for the cam being used. The innards of an engine that swallowed a valve are not a pretty sight.