12 within the guide openings 36 for valve train actuation depending on the speed of valve lifter reciprocation the lost motion spring 18 may cause the valve lifters 12 to oscillate angularly thereby placing angular loads on the inserts 54 and the edges 44 46 of the guide openings 36 as the valve lifters 12 oscillate within the guide openings 36 the inserts 54 initially absorb the oscillations and the angular loads of the valve lifters 12 to minimize the loads exerted on the edges 44 46 when the load exerted by the valve lifters 12 increases sufficiently as at high engine speeds the inserts will yield and allow oscillations of the valve lifters 10 to exert increased force against the edges 44 46 of the guide openings 36 however the inserts still act to dampen the oscillations and angular loads exerted by the lifters 12 and reduce the load exerted on the edges 44 46 of the guide openings 36 since the lifter guide 30 and the edges 44 46 are formed of metal the edges are able to resist greater rotational loads than the inserts 54 thus the edges 44 46 resist the increased rotational loads exerted by the valve lifters 12 and maintain the angular positions of the valve lifters 12 relative to their respective cams 19 it is preferred that the inserts 54 should have a tight initial fit around the.