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There is considerable "slop" with all the gaskets, holes, brackets, pump & bolts that must align with one another. I do NOT tighten them while the engine is on the engine stand. I wait until the engine is mounted in the car when there is a load on the engine. When I have everything all assembled with sealant still wet and bolts finger-tight, engine sitting in place, only then do I tighten the water pump bolts. My thinking is that if the assembly is tightened when there is no weight-load on the engine (ie: in an engine stand), the possibility exists that the vertical loads and vibration loads could cause the gaskets/sealer bonds to fracture and therefore leak. I've mounted 4 different engines in this manner and have had zero leaks.