If It Is The Right Rear (use Motor Off Grab Rubber Boot Of Plug And Pull Off That Cylinder) ,re- Start Car.) Method ...is Knock Gone ? Yeah Well If It Is Then That Is The Same Cylinder That Only Doe's It Till Warm Up On My '58 352 Ci Engine. The Re-builder Says Thats The Way They All Sounded But Of Course Im In Tenneesse And So They Talk Different Here When Addressing The Customer At The Local Engine Rebuild Shop. Timing And Pertronix Ignition Unit Got My Knock Down To A Very Little Knocking At Col Start Up ..i Can Live With That As They Are Sure It's Not Rod Slap Etc.fyi.good Luck With Mechanical Expertise In Your Town Too!