GM 12631195 Piston,(W/Pinion)

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Before actual disassembly of the piston and connecting rod assemblies, some of the cylinder head and also the oil pan must be dismantled. The top end of the ring groove needs to be scraped with a fingernail; indelible ridges here must be reamed off as failure will cause a ring burst which will need a new piston. When you have cleared the ridges, ensure the engine is rotated in a manner that the crankshaft is on the top. Measure the dimension of the crank to engine block with feeler gauges which should be less than service limit, if not this is preferred by replacing a new connecting rod. All the connecting rods should be marked to indicate the four cylinders they belong to then, the connecting cap bolts should be removed, however the old connecting cap bolts should be retained for the purpose of the oil clearance exercise. Slowly lift the first connecting rod cap and push the bearing insert out of the cylinder head; the insert must not fall out, and the connecting rod/piston assembly must be pushed out through the top of the engine. Do the same for the other cylinders and then replace the connecting rod caps and bearing inserts; retaining the old ones to avoid loss in case they are needed later. Pistons and connecting rods are finally prepared for inspection and require overhaul. Whenever replacing the piston rings the end gaps need to be inspected and the piston ring side clearance should be set. Position the pistons /connecting rods assemblies and the new rings on checker boards in order to ensure matching before installation. Fit the top ring into the first cylinder and align it as well as possible with the cylinder walls, measure the end gap with the feeler gauges. If it is too small wash with water and if the gap is too narrow filing the ring ends will serve as the best way of widening it. Do this again and again, for each ring; follow the right sequences as well as the orientation in its installation. Just for installation, the cylinder walls must be clean, the edges have to be chamfered and the crankshaft is to be inserted. Remove any dirt from the bearing inserts and set the new ones in the connecting rod and cap, without any lubrication, and make sure they are well positioned. Align the gaps of the piston rings rightly and grease the piston and the rings and its installation may be done with the help of piston ring compressor. Slide in the piston / connecting rod assembly into the cylinder ensuring that the connecting rod is under the crankshaft journal. There should also be a check of connecting rod bearing oil clearance by way of Plastigage and ensure that the width is to the standard prescribed. If the clearance is wrong then cleanliness should be established and the journal diameter can be considered for new bearing inserts. After confirming the clearance, it will be necessary to lubricate the bearing faces, replace the rod cap with new bolts and tighten in accordance with the necessary parameters. This should be repeated for all the assemblies, and it is essential to keep them clean, and oriented in the right directions throughout the stages of the process. Last of all, turn the engine over with the crankshaft to feel for binding and for checking the connecting rod end play; adjust if any new component has been changed.

Repeat the process for the remaining assemblies.

Mark the connecting rods and caps for identification, then remove the connecting rod cap bolts.