The piston/connecting rod assemblies first require cleaning before any inspection could be done and also the original piston rings have to be removed from the pistons and new piston rings must be installed each time. With the help of a piston ring installation tool, retrieve the rings from the pistons without harming the rings in any way. Clean carbon off the top of the piston with a bare hand-held wire brush, or fine emery paper do not use a wire brush in a motor as this tends to wore down the soft alloy of the piston. The carbon buildup should be cleaned from the ring grooves using a piston ring groove cleaning tool, if not available, a fragment of the old ring can be employed, in this way the groove is cleared without scratching the metal, only carbon is to be removed. Once they have been cleaned, the piston/rod assemblies should be wiped clean with solvent and then blow dried with compressed air; the oil return holes on the back side of the ring grooves should be clear. If the pistons and cylinder walls are not scratted or excessively worn and if the engine block is not rebored then new pistons are not always required but new piston rings should always be fitted during a rebuild. Every piston in turn must be examined for fine cracks, scores, scuffs, pierced, and burned area since these may suggest overheated areas or abnormal combustion and recommend a study of the cooling and lubrication systems. Small pitting corrosion may point to coolant seepage into the combustion chamber or crankcase; correction of this is critical to avoid reoccurrence in the reborn engine. To the piston ring side clearance ,place a new piston ring in each groove, the gap should be measure cross several point in the groove in order to obtaining the accurate ring type for the correct groove. the piston to bore clearance can be done by boring a hole whose diameter can be measured and consequently comparing with the piston diameter to arrive at the clearance. If the desired clearance is in excess of the standard, then he block will require reboring and this will translate to change of pistons and of course, the rings. To check piston-to-rod clearance, pinch the piston and rotate the rod in the opposite direction; if the play is large enough, you should correct it, which may involve resizing the bush or buying new ones, as well as new pins at an automotive machine shop. If pistons need to be removed from the connecting rods then it should be also taken to the machine shop to check among other things for a bend and twist. Last, examine the connecting rods for cracks, and damage; lift the rod caps, clean bearing surfaces, look for nicks, or scratches, and replace old bearings and tighten the caps finger tight; in case of a connecting rod knock and if the engine is being rebuilt, new connecting rods are required.
Posted by FordPartsGiant Specialist 
