If you are installing a new flat tappet camshaft in your engine, you must install new lifters. The lifter/lobe contact area is under a tremendous amount of pressure, and the lifter and lobe must wear in together.
The following reasons why you must install new lifters:
• A new lifter has a slight “crown.” A new cam has a slightly tapered face that causes the lifter to rotate.
• Installing a new cam with used lifters creates a concentrated contact pattern on the edge of the cam lobe
• Eventually, the contact wears out the edge of the lobe and lifter. Soon, the cam lobe wears down and the lifter stops rotating .