Hello recently acquired a set of 273 rockers ,I want to install them on a hydraulic cam 340 and plan on getting pushrod length checked for the right length pushrod...but my question is the set of rockers I acquired came with shims(cupped washers)...what is the reason for the shims?...is this an old trick to use on hydraulic cam?...just curious..I'm probably not even gonna keep the shafts because they don't have banana groves and I wanted hard chrome ones like rocket has...or do I need...should I modify mine with grooves?..thanks any advice is appreciated, Will