As is stated above many 351C catastrophic engine failures were caused by valve failure. The multi-groove keepers were actually designed to touch each other on both faces when installed The thought was it would allow the valve to rotate. Why it was thought to be beneficial is unknown to me, perhaps even wear on seats and guides. Because the keepers actually touch on both faces the valve is not held tightly allowing it to move side to side slightly which hammers the grooves on the valve stem and keepers causing failure of one or both (this is worsened by excessive guide wear and high RPM). The end result is the engine swallows the valve and grenades (literally) the engine. The real fix is to, as suggested, replace the valves with single groove valves and keepers. If that is not possible use hardened after market multi-groove keepers that positive lock on to the valve and do not allow it to rotate. The valve springs supplied in your kit have a specified installed spring height dimension, make sure it is correct. If it is not there are several ways to correct (valve spring shims, spring cups, offset keepers, retainers). Also beware of replacement rocker arm fulcrums. In the past I experienced multiple failures of after market fulcrums. Valve train geometry is very important for optimal performance and longevity. If the heads are milled, the block is decked, the seats are high or deep, or more likely a combination of the above, you may need a non-stock push rod length. As with cam timing, multiple small errors add up and cause less than desired performance problems that are hard to diagnose after assembly.
WOW somebody else with my luck
