4 Next, we bolted the bellhousing onto the engine and checked concentricity of the transmission input housing to the centerline of the crankshaft. This is often disregarded as an unnecessary step during assembly. It's rare to find a concentric bellhousing, and if the concentricity is off, the transmission life will be shortened and vibration can occur. You can contact www.keislerauto.com for the concentricity requirements. all kits come with a comprehensive instruction package to properly measure and explain how to adjust the concentricity to the maximum allowed specifications.