GM 24505686 Piston Assembly, (W/ Pinion, Std)

Remove the oil pan, oil pump, and cylinder heads as previously described. Before forcing the piston assemblies up through the top of the engine block, use a ridge reamer to eliminate the ridge or carbon deposits at the top of each cylinder. Work on one cylinder at a time by turning the engine so the piston is at the bottom of its stroke, placing a rag on top of the piston to catch the cuttings. After removing the ridge, crank the engine until the piston is at the top of the cylinder and then remove the cloth and cuttings, as failure to do so may damage the piston rings, pistons, or cylinder walls. Inspect the connecting rods and connecting rod caps for cylinder identification; if not plainly marked, use a small punch to make indentations (left bank-1, 3, 5, 7, right bank-2, 4, 6, 8). Remove the nuts on the connecting rod stud in sequence and lift the cap (with bearing inside) off the crankshaft, placing the connecting rod cap and bearing on a clean work surface marked for each cylinder. Cover the connecting rod studs with rubber or plastic tubing to prevent damage to the crankshaft or cylinder wall during piston assembly removal. Push the piston/connecting rod assembly out through the top of the cylinder and place it next to its rod cap on the sequenced work area. Repeat these procedures for the remaining seven cylinders, turning the crankshaft as necessary to access the connecting rod nuts, and reuse the rubber or plastic tubing for each assembly. Remove the bearings from the connecting rods and connecting rod caps using a small screwdriver; if the engine has many miles, it is not advisable to reuse the bearings, but if they are to be reinstalled, place them in a numbered rack. If a piston ring expanding tool is available, use it to remove each of the rings from the piston; alternatively, expand the ring just enough to clear the lands of the piston body, then place strips of tin (about ¾ in. wide) under the ring at equal distances around the piston and use a slight twisting motion to 'walk' the ring up and off the top. Place the rings in their 'installed' order adjacent to the piston/connecting rod on the numbered work area. Separating the connecting rod from the piston requires the removal of the piston pin, a task best left to a dealer or automotive machine shop equipped with the proper support tools and an arbor press. Avoid cleaning and inspecting the piston/rod assemblies at this time, as they may need to be replaced with new units depending on the condition of the cylinder block or crankshaft.

Most of the time, where engine has high numbers, original pistons are replaced since cylinder usually has to be bored larger for normal wear, although old pistons can be reused if finish honing and the condition of cylinder walls are good. The connecting rods and pistons should be cleaned in a cleaning solvent and dried in compressed air; it is forbidden to use wire brushes or any other abrasive cleaning tools on the piston. Cleaning of the piston rings should be with the groove cleaner tool and the oil ring holes/slots should be clean. The rods must be twist and bend checked and it must be inspected for nicks or cracks: any of these would be a sign that the rod must be replaced. The piston should be checked for crack in ring land, skirt or pin bosses, worn or wavy ring land, scuffed or damaged skirt and eroded area on top; if the piston is bad or has signs of excessive wear, it must be replaced. Further, the ring grooves should be checked to see that there are no nicks on the ring which may cause it to hang and therefore retard the motion of the other rings. Before disconnecting the connecting rods from the pistons it is necessary to turn aside the rods to get the degree of their difficulty in rotation all the piston/rod assemblies; if the rods are loose on the piston pins and turn round the pins easily or with little resistance then the pistons have worn and the pins is worn out and must be renewed. If there is a need to machine any part of the cylinder block like the final honing then one is most likely to find that the machinist would want to have the pistons around to check the piston to bore clearance as the bore is machined the clearance is very important and hence best to be done by the technician.

After all assemblies are installed, rotate the crankshaft to check for binding, and finally, check the connecting rod end-play against specifications.

Slip a short length of plastic or rubber hose over each connecting rod cap bolt.