In high rpm situations (and when used in conjunction with high valve spring pressures) the OEM cageless trunion needle bearings’s outer shell may tend to begin walking out of the rocker arm’s pivot trunion bore, resulting in individual needle bearings quickly falling out and scattering throughout the engine (the OE needles are captured by two separate housings, and the outer housing tends to walk out, releasing the needles). Obviously, this isn’t good for either the rockers (no bearings) or the rest of the engine. Don't risk the longevity of your engine