GM 25527178 Piston, W/Pinion(Std High, Limit)

It is often long mileages where original pistons must be changed because of bores enlarged for normal wear and for connecting rods, although old pistons may be utilized occasionally if the cylinder walls require little more than final finishing and are still in satisfactory state. Connecting rods and pistons must be cleaned with cleaning solvent and blow with compressed air not to use wire brushes or any abrasive tool on any part of the piston. The ring grooves of the piston must be cleaned using a groove cleaner tool; where oil ring holes or slots are found and or present they must be clean. Care should be taken when inspecting the rods to ensure that they do not display signs of twist, bending, nicking or crack; in such cases they should be replaced. This covering should be checked for cracked ring lands, skirts or pin bosses, as well as worn or damaged areas and damaged pistons have to be replaced. Grooves on rings should be inspected for nicks which if present could slow the ring down. When the piston is still attached to the connecting rod, the piston should be rocked side to side to determine the degree of effort as compared between all pinston/rod assemblies; if the rods are loose on the piston pins with or with no drag, the pins are worn and should be replaced. If in any case the cylinder block requires some machine work to be done, such as finish honing, it is always best to bring the pistons to check the piston to bore clearance and this is better done in the machine shop.

Check bearing clearance using Plastigage®. If clearance is excessive, select the correct undersized bearing shell.

Finally, reassemble the engine components, such as the oil pump, oil pan, cylinder head(s), and intake manifold.

Verify that the piston/rod assembly is correctly positioned by checking that most pistons are marked with an 'F' or a drilled-out area indicating the front of the engine, and ensure that the rod bearing tang slots are towards the outside of the engine block once installed.

Remove the nuts on the connecting rod stud in sequence and lift the cap off the crankshaft.

Finally, check the clearance of the piston rings in their grooves with a blade feeler gauge, rotating it around the piston to ensure proper clearance, and replace or adjust as necessary.

Use a small screwdriver to remove the bearings, considering the condition of the engine before deciding to reuse them.

The ring grooves should be cleaned with a groove cleaner tool, ensuring that the oil ring holes and slots are also clean.

Lubricate the connecting rod bearings and install them into their appropriate rod and rod cap.

Additionally, measure the end gap of each second ring and oil control ring.

It is important to check that all the piston ring gaps are positioned properly.

Install the bottom oil ring spacer and its components, ensuring they are free in the groove, and repeat the process for all piston assemblies.

The piston should be examined for cracked ring lands, skirts, or pin bosses, as well as worn or wavy ring lands, scuffed or damaged skirts, and eroded areas at the top. Any damaged pistons or those showing excessive wear must be replaced.

The first step is to remove the oil pan, oil pump, and cylinder heads as previously described.