Just purchased a 71 mach 1 with a 351 Clevland engine. When the engine heats up I get a valve tap that is pretty loud. Looked on the internet about adjusting the Lifters and they talk about 0 lash and ECT. I pulled the covers and there is no adjustment! the nuts are as tight as they will go on all lifters. Some of the push rode can spin while others are tight. does anyone know anything about this engine??? A friend told me there is no adjustment on the clevland lifters yet all over the internet they say they can be adjusted.