GM 91177382 Piston Kit,Os:050 (On Esn)

Before going through the inspection process, clean the piston/rod assemblies and remove the original piston rings. When you reassemble the engine, make sure to use new piston rings. Using a piston ring installation tool, gently take off the rings from the pistons trying not to spoil them. Simply scrape away carbon deposits on top of the piston then use a hand-held wire brush or fine emery cloth after most of it is gone. Do not use a wire brush in a drill motor because it can erode the soft material of the piston. Take out all carbon from ring grooves using either a tool for cleaning grooves or broken old rings without removing metal or damaging side faces of grooves. Having removed the deposits, wash off pistons/rods using solvent and dry up with compressed air ensuring clear oil return holes at back sides of ring grooves. In case pistons and cylinder walls are not significantly damaged or worn excessively and if there is no need for reboring an engine block, then new pistons may not be necessary; otherwise when overhauling an engine always replace with new ones. Examine each piston carefully for any signs of cracks around its skirt, pin bosses as well as ring lands. Watch out for scores at scuffing points on skirts thrust faces, pit marks in crown that look like worm holes and burnt edges around upper part pointing to probable overheating or an abnormal combustion problem. Check what causes include intake air leaks, wrong fuel/air mixture ratios, timing differences or EGR system failures (Garrett 460). If you see small pits, corrosion means coolant leakage into combustion chamber or crankcase requiring correction. Measure both piston ring side clearance and bore-to-piston clearance to ensure they are in specifications. Confirmations about piston-to-rod clearance may be obtained from an automotive machine shop if need be. Should one require separating pistons from connecting rods he should consult an automotive machine shop. Inspect rods for cracking and damage, take off rod caps for bearing surface inspection purposes only to replace old bearings when an engine is being rebuilt as a result of connecting rod knock and make sure that new rods are installed where necessary.

It is important to check for ridges in the cylinder because carbon deposits or cylinder wear can produce ridges at the upper limit of ring travel. These ridges must be completely removed before attempting to remove the piston/connecting rod assemblies to avoid piston breakage.

After the piston/connecting rod assembly is installed in the cylinder, the connecting rod bearing oil clearance should be checked using Plastigage.