See Figures 1, 2, 3, 4, 5 and 6
Although in some cases the pistons and connecting rods may be removed with the engine still in the vehicle, it is rarely worth the aggravation, especially when you are not working with a lift. On vehicles where this is possible (cylinder head and oil pan removal are both possible with the engine installed and there is sufficient working clearance) take EXTREME care to assure no dirt or contamination is allowed into the cylinders during assembly and installation.
Before removing the pistons, the top of the cylinder bore must be examined for a ridge. A ridge at the top of the bore is the result of normal cylinder wear, caused by the piston rings only traveling so far up the bore in the course of the piston stroke. If the ridge can be felt by hand; it must be removed before the pistons are removed.
A ridge reamer is necessary for this operation. Place the piston at the bottom of its stroke, and cover it with a rag. Cut the ridge away with the ridge reamer, using extreme care to avoid cutting too deeply. Remove the rag, and remove the cuttings that remain on the piston with a magnet and a rag soaked in clean oil. Make sure the piston top and cylinder bore are absolutely clean before moving the piston. For more details, refer to the ridge removal and honing procedures later in this section.
- Remove cylinder head or heads.
- Remove the oil pan.
- If necessary, remove the oil pump assembly.
- Matchmark the connecting rod cap to the connecting rod with a scribe; each cap must be reinstalled on its proper rod in the proper direction. Remove the connecting rod bearing cap and the rod bearing. Number the top of each piston with silver paint or a felt-tip pen for reference during assembly.
- Cut lengths of 3 / 8 in. (10mm) diameter hose to use as rod bolt guides. Install the hose over the threads of the rod bolts, to prevent the bolt threads from damaging the crankshaft journals and cylinder walls when the piston is removed.
- Squirt some clean engine oil onto the cylinder wall from above, until the wall is coated. Carefully push the piston and rod assembly up and out of the cylinder by tapping on the bottom of the connecting rod with a wooden hammer handle.
- Place the rod bearing and cap back on the connecting rod, and install the nut temporarily. Using a number stamp or punch, stamp the cylinder number on the side of the connecting rod and cap; this will help keep the proper piston and rod assembly on the proper cylinder.
- Remove remaining pistons in similar manner.
- Clean and inspect the engine block, the crankshaft, the pistons and the connecting rods.
CLEANING AND INSPECTION
See Figures 7, 8, 9, 10, 11 and 12Pistons
A piston ring expander is necessary for removing piston rings without damaging them; any other method (screwdriver blades, pliers, etc.) usually results in the ring being bent, scratched or distorted, or the piston itself being damaged. When the rings are removed, clean the piston grooves using an appropriate ring groove cleaning tool, using care not to cut too deeply. Thoroughly clean all carbon and varnish from the piston with solvent.
Clean the varnish from the piston skirts and pins with a cleaning solvent. DO NOT WIRE BRUSH ANY PART OF THE PISTON. Clean the ring grooves with a groove cleaner and make sure that the oil ring holes and slots are clean.
Inspect the piston for cracked ring lands, scuffed or damaged skirts, eroded areas at the top of the piston. Replace the pistons that are damaged or show signs of excessive wear.
Inspect the grooves for nicks of burrs that might cause the rings to hang up.
Measure the piston in relation to cylinder diameter. Refer to the cylinder bore cleaning and inspection procedures later in this section.
Wash the connecting rods in 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.Cylinder Bores
The piston should also be checked in relation to the cylinder diameter. Using a telescoping gauge and micrometer, or a dial gauge, measure the cylinder bore diameter perpendicular (90 degrees) to the piston pin, about 1-2 1 / 2 in. (25-64mm) below the cylinder block deck (surface where the block mates with the heads). Then, with the micrometer, measure the piston perpendicular to its wrist pin on the skirt. The difference between the two measurements is the piston clearance.
If the clearance is within specifications or slightly below (after the cylinders have been bored or honed), finish honing is all that is necessary, If the clearance is excessive, try to obtain a slightly larger piston to bring the clearance within specifications. If this is not possible obtain, the first oversize piston and hone the cylinder or (if necessary) bore the cylinder to size. Generally, if the cylinder bore is tapered more than 0.005 in. (0.127mm) or is out-of-round more than 0.003 in. (0.0762mm), it is advisable to rebore for the smallest possible oversize piston and rings. After measuring, mark the pistons with a felt-tip pen for reference and for assembly.
Boring of the cylinder block should be performed by a reputable machine shop with the proper equipment. In some cases, clean-up honing can be done with the cylinder block in the vehicle, but most excessive honing and all cylinder boring MUST BE done with the block stripped and removed from the vehicle.
RIDGE REMOVAL & HONING
See Figures 13, 14 and 15
- Before the piston is removed from the cylinder, check for a ridge at the top of the cylinder bore. This ridge occurs because the piston ring does not travel all the way to the top of the bore, thereby leaving an unworn portion of the bore surface.
- Clean away any carbon buildup at the top of the cylinder with sand paper, in order to see the extent of the ridge more clearly. If the ridge is slight, it will be safe to remove the pistons without damaging the rings or piston ring lands. If the ridge is severe, and easily catches your fingernail, it will have to be removed using a ridge reamer.
A severe ridge is an indication of excessive bore wear. Before removing the piston, check the cylinder bore diameter with a bore gauge, as explained in the cleaning and inspection procedure. Compare your measurement with engine specification. If the bore is excessively worn, the cylinder will have to bored oversize and the piston and rings replaced.
- Install the ridge removal tool in the top of the cylinder bore. Carefully follow the manufacturers instructions for operation. Only remove the amount of material necessary to remove the ridge. Place the piston at the bottom of its stroke, and cover it with a rag. Cut the ridge away with the ridge reamer, using extreme care to avoid cutting too deeply. Remove the rag, and remove the cuttings that remain on the piston with a magnet and a rag soaked in clean oil. Make sure the piston top and cylinder bore are absolutely clean before moving the piston.
- After the piston and connecting rod assembly have been removed, check the clearances as explained earlier in this section under the cleaning and inspection procedure, to determine whether boring and honing or just light honing are required. If boring is necessary, consult an automotive machine shop. If light honing is all that is necessary, proceed with the next step.
- Honing is best done with the crankshaft removed, to prevent damage to the crankshaft and to make the post-honing cleaning easier, as the honing process will scatter metal particles. However, if you do not want to remove the crankshaft, position the connecting rod journal for the cylinder being honed as far away from the bottom of the cylinder bore as possible, and wrap a shop cloth around the journal.
- Honing can be done either with a flexible glaze breaker type hone or with a rigid hone that has honing stones and guide shoes. The flexible hone removes the least amount of metal, and is especially recommended if your piston-to-cylinder bore clearance is on the loose side. The flexible hone is useful to provide a finish on which the new piston rings will seat. A rigid hone will remove more material than the flexible hone and requires more operator skill.
- Regardless of which type of hone you use, carefully follow the manufacturers instructions for operation.
- The hone should be moved up and down the bore at sufficient speed to obtain a uniform finish. A rigid hone will provide a definite cross-hatch finish; operate the rigid hone at a speed to obtain a 45-65 degree included angle in the cross-hatch. The finish marks should be clean but not sharp, free from embedded particles and torn or folded metal.
- Periodically during the honing procedure, thoroughly clean the cylinder bore and check the piston-to-bore clearance with the piston for that cylinder.
- After honing is completed, thoroughly wash the cylinder bores and the rest of the engine with hot water and detergent. Scrub the bores well with a stiff bristle brush and rinse thoroughly with hot water. Thorough cleaning is essential, for if any abrasive material is left in the cylinder bore, it will rapidly wear the new rings and the cylinder bore. If any abrasive material is left in the rest of the engine, it will be picked up by the oil and carried throughout the engine, damaging bearings and other parts.
- After the bores are cleaned, wipe them down with a clean cloth coated with light engine oil, to keep them from rusting.
- Lubricate each piston, rod bearing, and cylinder wall with heavy weight engine oil.
- Take the bearing nuts and cap off connecting rod. Install rubber hoses over the connecting rod bolts to protect the block and crankshaft journal.
- Install a ring compressor over the piston, position piston with the mark toward front of engine and carefully install.
- Position the connecting rod with bearing insert over the crank journal. Install the rod cap with bearing in proper position. Secure with rod nuts and torque to the proper specifications. Install all of the rod and piston assemblies.
PISTON RING REPLACEMENT
- 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 25mm 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 specifications table. If the measurement is too small, when the engine heats up the ring ends will butt together and cause damage. File the ends of the ring with a fine file to obtain necessary clearance.
If inadequate ring end gap is utilized, ring breakage will result.
- 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. The machine shop can handle the 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 with a fine file. Hold the ring in the groove and measure side clearance with a feeler gauge. If the clearance is excessive, spacer(s) will have to be added.
Always add spacers above the piston ring.
- Install the ring on the piston, lower oil ring first. Use a ring installing tool (piston ring expander) 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 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 25mm away from the butted end of the control ring. Install the top rail about 25mm away from the butted end of the control but on the opposite side from the lower rail. Be careful not to scrap the piston when installing oil control rings.
- Install the two compression rings. The lower ring first.
- Consult the illustration for ring positioning, arrange the rings as shown, install a ring compressor and insert the piston and rod assembly into the engine.
PISTON PIN REPLACEMENT
- Matchmark the piston head and the connecting rod for reassembly.
- Position the piston assembly in a piston pin removal tool.
- Following the tool manufacturers instructions, press the piston pin from the piston.
- Check the piston pin bore for damage, replace defective components as required. Check the piston pin for damage, replace as required.
- Installation is the reverse of the removal procedure.
ROD BEARING REPLACEMENT
- Remove the engine from the vehicle. Position the engine assembly in a suitable holding fixture.
- Remove the oil pan. Remove the oil pump, as required.
- Rotate the crankshaft so that you can remove the rod bearing cap. Matchmark the rod bearing cap so that it can be reinstalled properly.
- Remove the rod bearing cap. Remove the upper half of the bearing from its mounting.
- Carefully remove the lower half of the bearing from its mounting. It may be necessary to push the piston down in the cylinder bore to to this.
- Installation is the reverse of the removal procedure.