Originally Posted by Pattojnr
Razzor, i have seen 3 Nova LS3 engines now , including my own. when the bearings wear, the inward outward movement in the crank is causing the conrod to rub on the back plate. this is causing a problem with trying to tune the engine in a false manner. its ok when cold but when at temps the tune becomes erratic and feels as though it hasnt enough fuel. so you richen it up, and then it bogs down. thing is to get on to replacing the bearings fairly quickly as this can cause a motor failure. the conrod can move that much and cause extra heat and wear. the front bearing starts to run on the alloy of the block, and fuel leakage is evident from the front bearing.
even on a brand spankin' new engine there is fore/aft crank play, or else the crank pin would already be hitting the backplate. Does that mean the bearings are bad from the factory?? These parts are batch produced, slapped together, and vary from engine to engine.... even of the same type.
Crank pins and journal widths have a tolerance, blocks have a bearing bore depth tolerance, rods have a width tolerance, backplates have a depth tolerance, etc.... stack them all up in the right direction and you have more play in one engine than the next engine.