Buick 12539085 Piston, (W/Pinion)

Prior to removing the piston and connecting rod assemblies, the cylinder head(s), oil pan, and oil pump must be taken off, depending on the engine type. First, use your fingernail to check for any ridges at the upper limit of ring travel, which is about 1/4-inch down from the top of each cylinder. If ridges are present due to carbon deposits or cylinder wear, they must be completely removed with a ridge reamer before attempting to remove the pistons to avoid breakage. After removing the cylinder ridges, turn the engine upside-down with the crankshaft facing up. Before removing the connecting rods, check the endplay using feeler gauges; if the endplay exceeds the service limit, new connecting rods may be necessary. Ensure the connecting rods and caps are marked for identification, and if not, use a center-punch to create indentations. Loosen the connecting rod cap nuts gradually until they can be removed by hand, then take off the number one connecting rod cap and bearing insert without dropping the insert. To protect the crankshaft journal and cylinder wall during piston removal, slip a short length of plastic or rubber hose over each connecting rod cap bolt. Remove the bearing insert and push the connecting rod/piston assembly out through the top of the engine, using a wooden or plastic hammer handle if needed. Repeat this process for the remaining cylinders. After removal, reassemble the connecting rod caps and bearing inserts in their respective rods and install the cap nuts finger tight to prevent damage to the bearing surfaces. It is important not to separate the pistons from the connecting rods.

When bolting the piston and connecting rods it is necessary to check that the cylinder walls are free from dirt, each cylinder top edge should be chamfered and the crankshaft in position. Take off the cap of the number one connecting rod and be sure to have it noted from the marks that were made as the cap was being removed in the process should it be required again later then clean the bearing surfaces using a lint free cloth. Do not touch the new bearing inserts with fingers so as not to expose them to contamination. My first step is to as clean the back side of the new upper bearing insert and place it in the connecting rod in such a manner that the tab will fit in to the recess without having to hammer it in. Do the same for the lower bearing insert in the rod cap being careful not to compromise the cleanliness of the area. Align the three gaps in the pistons at possibilities of 120 degrees, apply a thin layer of engine oil on the pistons and the rings and then to install the piston into the cylinders, you need to use the piston ring compressor. Turn the crankshaft until the number one connecting rod journal aligns with the bottom dead centre and lubricate the cylinder walls. Swing the piston/connecting rod assembly into the cylinder bore-the notch or arrow on the piston should be oriented towards the front of the engine-and tap it home gently whilst slotting the connecting rod onto the crank journal. After the installation is complete it is important to check the oil clearance of the connecting rod bearing by using Plastigage and make sure that the alignment is well done on the cap and the rod. After that, turn the nuts until they reach the designed torque, in three-quarter turns, and thereafter unbolt the rod cap in such a manner that doesn't affect the Plastigage. Use the width of the crushed Plastigage to obtain the oil clearance and in case it's out of range look for dirt or oil contamination then recheck the journal diameter. Remove any Plastigage from the rod journal and bearing face, then coat them with moly-base grease or engine assembly lube; put the connecting rod and cap back on and fasten nuts to the proper torque. The next step is to follow one and the same procedure with other pistons and connecting rods and to pay attention to their orientation and the marks on the pistons. Following the installation of all assemblies, rotate the crankshaft and look for binding, and the last one is the connect rod small end clearance check to the specification, if it does not meet the requirements, resize the rods.

A piston ring groove cleaning tool should be used to eliminate carbon deposits from the ring grooves. Alternatively, a piece broken off the old ring can serve the same purpose, but care must be taken not to remove any metal or damage the grooves.