See Figures 1, 2 and 3
Although, in most cases, the pistons and connecting rods can be removed from the engine (after the cylinder head and oil pan are removed) while the engine is still in the car, it is far easier to remove the engine from the car. If removing pistons with the engine still installed, disconnect the radiator hoses, automatic transmission cooler lines, if so equipped, and radiator shroud. Unbolt front mounts before jacking up the engine. Block the engine in position with wooden blocks between the mounts.
- Remove the engine from the car, as previously covered in this section.
- Remove the cylinder head(s), oil pan and front cover (if necessary).
- Using a ridge reamer, remove the ridge at the top of each cylinder bore, before removing the pistons and connecting rods. (Refer to the following section on Ridge Removal.)
- Check the edges of the connecting rod and bearing cap for numbers or matchmarks. If none are present, mark the rod and cap numerically and in sequence from the front to back of the engine. The numbers or marks not only tell from which cylinder the piston came, but also ensures that the rod caps are installed in the correct matching position.
- Turn the crankshaft until the connecting rod is at the bottom of its travel. Remove the two attaching nuts and the bearing cap. Take two pieces of rubber tubing and cover the rod bolts to prevent crankshaft or cylinder scoring. Use a wooden hammer handle to help push the piston and rod up and out of the cylinder. install the rod cap in its proper position. Remove all pistons and connecting rods, in this manner. Inspect the cylinder walls and deglaze or hone as necessary. (Refer to the following section on Cylinder Honing.)
CLEANING AND INSPECTION
See Figures 4 and 5
- Use a piston ring expander and remove the rings from the piston.
- Clean the ring grooves using an appropriate cleaning tool, exercising care to avoid cutting too deeply.
- Clean all varnish and carbon from the piston with a safe solvent. Do not use a wire brush or caustic solution on the pistons.
- Inspect the pistons for scuffing, scoring, cracks, pitting or excessive ring groove wear. If wear is evident, the piston must be replaced.
- Have the piston and connecting rod assembly checked by a machine shop for correct alignment, piston pin wear and piston diameter. If the piston has collapsed, it will have to be replaced or knurled to restore its original diameter. Connecting rod bushing replacement, piston pin fitting and piston changing can be handled by the machine shop.
Check used piston-to-cylinder bore clearance as follows:
- Measure the cylinder bore diameter with a telescope gauge.
- Measure the piston's outer diameter with a micrometer. When measuring the pistons for size or taper, measurements must be made with the piston pin removed.
- Subtract the piston diameter from the cylinder bore diameter to determine piston-to-bore clearance.
- Compare the piston-to-bore clearances obtained with those clearances recommended. Determine if the piston-to-bore clearance is in the acceptable range.
- When measuring taper, the largest reading must be at the bottom of the skirt. SELECTING NEW PISTONS
See Figures 6 and 7
- If the used piston is not acceptable, check the service piston size and determine if a new piston can be selected. (Service pistons are available in standard, high limit and standard oversize.
- If the cylinder bore must be reconditioned, measure the new piston diameter, then hone the cylinder bore to obtain the preferred clearance.
- Select a new piston and mark the piston to identify the cylinder for which it was fitted. On some vehicles, oversize pistons may be found. These pistons will be 0.010 in. (0.254mm) oversize.
See Figures 8 and 9
Because the top piston ring does not travel to the very top of the cylinder bore, a ridge is built up between the end of the travel and the top of the cylinder. Pushing the piston and connecting rod assembly past the ridge is difficult and may cause damage to the piston. If new rings are installed and the ridge has not been removed, ring breakage and piston damage can occur when the ridge is encountered at engine speed.
- Turn the crankshaft to position the piston at the bottom of the cylinder bore. Cover the top of the piston with a rag.
- Install a ridge reamer in the bore and follow the manufacturer's instructions to remove the ridge. Use caution to avoid cutting too deeply or into the ring travel area.
- Remove the rag and cuttings from the top of the piston.
- Remove the ridge from each of the other cylinders, using the same procedure.
See Figures 10 and 11
Check the cylinder bore for wear using a telescope gauge and a micrometer. Measure the cylinder bore diameter perpendicular to the piston pin at the point 2 1 / 2 in. (63.5mm) below the top of the engine block. Measure the piston skirt perpendicular to the piston pin. The difference between the two measurement is the piston clearance. If the clearance is within specifications, finish honing or glaze breaking is all that is required. If clearance is excessive, a slightly oversized piston may be required. If greatly oversize, the engine will have to be bored and 0.010 in. (0.254mm) or larger oversized pistons installed.
- When cylinders are being honed, follow the manufacturer's recommendations for the use of the hone.
- Occasionally, during the honing operation, the cylinder bore should be thoroughly cleaned and the selected piston checked for correct fit.
- When finish-honing a cylinder bore, the hone should be moved up and down at a sufficient speed to obtain a very fine uniform surface finish in a cross-hatch pattern of approximately 45-65° included angle. The finish marks should be clean, but not sharp, and free from imbedded particles and torn or folded metal.
- Permanently mark the piston for the cylinder to which it has been fitted and proceed to hone the remaining cylinders.
- Thoroughly clean the bores with hot water and detergent. Scrub well with a stiff bristle brush and rinse thoroughly with hot water. It is extremely essential that a good cleaning operation be performed. If any of the abrasive material is allowed to remain in the cylinder bores, it will rapidly wear the new rings and cylinder bores. The bores should be swabbed several times with light engine oil and a clean cloth, and then wiped with a clean dry cloth. CYLINDERS SHOULD NOT BE CLEANED WITH KEROSENE OR GASOLINE. Clean the remainder of the cylinder block to remove the excess material spread during the honing operation.
PISTON PIN REPLACEMENT
Use care at all times when handling and servicing connecting rods and pistons. To prevent possible damage to these units, do not clamp the rods or pistons in a vise, since they may become distorted. Do not allow the pistons to strike against one another, or against hard objects or bench surfaces, since distortion of the piston contour or nicks in the soft aluminum material may result.
- Remove the piston rings using a suitable piston ring remover.
- Remove the piston pin lockring, if used. Install the guide bushing of the piston pin removing and installing tool.
- Install the piston and connecting rod assembly on a support, and place the assembly in an arbor press. Press the pin out of the connecting rod, using the appropriate piston pin tool.
- Assembly is the reverse of disassembly. Use new lockrings where needed.
PISTON RING REPLACEMENT
See Figures 12 through 16
- Take the new piston rings and compress them, one at a time into the cylinder that they will be used in. Press the ring about 1 in. (25.4mm) below the top of the cylinder block using an inverted piston.
- Use a feeler gauge and measure the distance between the ends of the ring; this is called measuring the ring end-gap. Compare the reading to the one called for in the specification table. File the ends of the ring with a fine file to obtain the necessary clearance.
- Inspect the ring grooves on the piston for excessive wear or taper. If necessary, have the grooves recut for use with a standard ring and spacer. A machine shop can handle this job for you.
- Check the ring grooves by rolling the new piston ring around the groove to check for burrs or carbon deposits. If any are found, remove them with a fine file. Hold the ring in the groove and measure side clearance with a feeler gauge. If clearance is excessive, spacer(s) will have to be added.
Always add the spacer above the piston ring.
- Install the rings on the piston, lower oil ring first. Use a ring installing tool on the compression rings. Consult the instruction sheet that comes with the rings to be sure they are installed with the correct side up. A mark on the ring usually faces upward.
- When installing the oil rings, first install the expanding ring in the groove. Hold the ends of the ring butted together (they must not overlap) and install the bottom rail (scraper) with the end about 1 in. (25.4mm) away from the butted end of the control ring. Install the top rail about 1 in. (25.4mm) away from the butted end of the control, but on the opposite side from the lower rail.
- Install the two compression rings.
- Consult the illustration for ring positioning, and arrange the rings as shown.
- Install a ring compressor and insert the piston and rod assembly into the engine.
ROD BEARING REPLACEMENT
See Figures 17 through 23
Rod bearings can be installed when the pistons have been removed for servicing (rings, etc.) or, in most cases, while the engine is still in the car. Bearing replacement, however, is far easier with the engine out of the car and disassembled.
Wash the connecting rods in a cleaning solvent and dry with compressed air. Check for twisted or bent rods and inspect for nicks or cracks. Replace connecting rods that are damaged.
Inspect journals for roughness and wear. Slight roughness may be removed with a fine grit polishing cloth saturated with engine oil. Burrs may be removed with a fine oil stone by moving the stone on the journal circumference. Do not move the stone back and forth across the journal. If the journals are scored or ridged, the crankshaft must be replaced.
The connecting rod journals should be checked for out-of-roundness and correct size with a micrometer.
Connecting rod journals will normally be standard size. If any undersized bearings are used, the size will be stamped on a counterweight.
If plastic gauging material is to be used:
- Clean oil from the journal bearing cap, connecting rod and outer and inner surfaces of the bearing inserts. Position the insert so that the tang is properly aligned with the notch in the rod and cap.
- Place a piece of plastic gauging material, such as Plastigage®, in the center of the lower bearing shell.
- Remove the bearing cap and determine the bearing clearances by comparing the width of the flattened plastic gauging material at its widest point with the graduation on the package. The number within the graduation on the package indicates the clearance in thousandths of an inch or millimeters.
If this clearance is excessive, replace the bearing insert and recheck the clearance with the plastic gauging material. Lubricate the bearing insert with engine oil before assembly. Repeat the procedure on the remaining connecting rod bearings. All rods must be connected to their journals when rotating the crankshaft, to prevent engine damage.
- Clean the rod journal, the connecting rod end and the bearing cap after removing the old bearing inserts.
- Install the new bearing inserts in the connecting rod and bearing cap, with the tangs fitting in the slots provided and lubricate them with oil.
- Lubricate the bearing inserts with oil.
- Position the connecting rod over the crankshaft journal and install the rod cap. Make sure the cap and rod numbers match, and torque the rod nuts to specification.
- Lubricate the piston, bearing inserts and cylinder wall.
- Install a ring compressor over the piston, position the piston with the mark toward the front of the engine, and carefully install.
- Position the connecting rod with the bearing insert installed over the crankshaft journal. Install the connecting rod cap with the bearing in its proper position. Secure with rod nuts and torque to the proper specification.
- Install the remaining rod and piston assemblies in the same manner.
- If removed, replace the front cover and gasket or seal.
- Install the oil pan and cylinder head(s).
- Install the engine in the car, as previously covered in this section.