These Evolution tappet block kits for Big Twin motors are produced to improve the stock tappet and tappet block area. Made from billet 7075-T651 aluminum with a tensile strength 3 times stronger than cast aluminum tappet blocks. These tappet block are machined to the center line of the cam and hold approximate .002", also the bores are held perpendicular to the mounting flange to approximate .0002". Designed to accommodate a gross valve lift of .550" at the valves, this is about .350" at the tappets, leaving a clearance of .035" roller to block free play (please note, if using a cam with a higher lift, a simple modification is all that is needed). These blocks will clear most small circle cams having a lift of .600" or more. Add the precision quality of Jims Big Axle tappets and you can't buy a better tappet block kit for your bike. These kits come complete with front and rear tappet block, 4 Big Axle PowerGlide tappets, tappet block gaskets and screws. Available for stock and stock style Evolution Big Twin crankcases from 1984 thru 1999.