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In contrast to a roller, a flat tappet must rotate in the lifter bore for survival. Lube a flat tappet with cam lube on the base and engine oil on its sides and oil the lifter bores. The lifter must slide easily in the bore, without any binding or tight spots. Some block cleaning procedures using shot tumblers can create a burr at the top of the lifter bores, causing binding. Always prep and check the lifter bores during the mock-up stage of engine assembly.