GMC 12674056 Piston Kit

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To remove the piston/connecting rod assemblies, first check for ridges formed at the upper limit of ring travel in each cylinder and remove them using a special tool to avoid piston breakage. Then, with the engine positioned so the crankshaft faces up, assess connecting rod endplay using feeler gauges and replace connecting rods if necessary. Mark the connecting rods and caps for identification and remove the cap bolts. Use new bolts for reassembly, but save the old ones for an oil clearance check. Carefully remove the number one connecting rod cap and bearing insert, followed by the bearing insert and the entire connecting rod/piston assembly, ensuring that the ridge was completely removed. Repeat this process for all cylinders, and reassemble the connecting rod caps and bearing inserts loosely to protect the bearing surfaces during further inspection and overhaul at an automotive machine shop. Before installing new piston rings, check the ring end gaps and ensure proper side clearance. Place the top ring into the first cylinder, measure the end gap with feeler gauges, and confirm it falls within the specified range. Adjust the gap if necessary, either by filing the ends to increase it or verifying you have the correct rings. Install the oil control ring components, followed by the number two and number one rings, making sure their orientation is correct and using a piston ring installation tool for the top and middle rings. Afterward, check and adjust the ring end gaps for all rings in each cylinder, keeping components matched. To install the piston/connecting rod assemblies, ensure clean cylinder walls, chamfer the top edges of the bores, and have the crankshaft in place. Remove the cap from the number one connecting rod, clean the bearing surfaces thoroughly, and lay in the new upper bearing insert. Then, insert the lower bearing insert in the cap, making sure the tab fits into the recess and keeping both mating surfaces clean and oil-free. Position the piston ring gaps correctly, lubricate the piston and rings with engine oil, and use a piston ring compressor to compress the rings. Insert the piston/connecting rod assembly into the cylinder bore, guiding the connecting rod onto the crankshaft journal with a gentle tap while being cautious not to force it. Check for any resistance and resolve issues before proceeding. Once installed, check connecting rod bearing oil clearance using Plastigage before permanently attaching the rod cap with new bolts. Ensure a clean surface and apply molybase grease or engine assembly lube to both bearing faces. Repeat this process for all pistons/connecting rods, confirming cleanliness, proper orientation, and lubrication. Rotate the crankshaft by hand to check for binding, and verify the connecting rod endplay, resizing them if necessary at an automotive machine shop.