See Figures 1 and 2
The notch on the top of each piston must face the front of the engine.
To position the connecting rod correctly, the oil squirt hole should point to the right side on all six-cylinder engines. On all V8 engines, the larger chamfer of the lower connecting rod bore must face to the rear on the right bank and to the front on the left bank.
See Figures 3 through 7
- Remove the cylinder head.
- Remove the timing chain/gears.
- Remove the oil pan.
- Pistons should be removed following the firing order of the engine. Turn the crankshaft until the piston to be removed is at the bottom of its stroke.
- Place a cloth on the head of the piston to be removed and, using a ridge reamer, remove the deposits from the upper end of the cylinder bore.
- Mark all connecting rod bearing caps so that they may be returned to their original locations in the engine. The connecting rod caps are usually marked. The marks must be matched when re-assembling the engine. Mark all pistons so they can be returned to their original cylinders.
After removing the connecting rod cap and bearing, place a short length of rubber hose over the rod bolts to prevent cylinder wall and crank journal scoring when removing or installing the piston and rod assembly.
- Carefully tap the piston out of the bore using a wooden dowel. Once the piston rings have cleared the top edge of the bore, remove the piston assembly from the engine.
- Disconnect the battery ground.
- Drain the cooling system.
- Drain the oil.
- Remove the dipstick and tube.
- Remove the road draft tube.
- Remove the automatic transmission cooling lines and bracket.
- Remove the oil pan.
- Remove the oil pick-up tube and gasket.
- Turn the crankshaft until the connecting rod journal of the piston to be removed is at bottom center. Remove the connecting rod cap nuts. Install short pieces of hose on the studs to prevent journal damage. Mark the rod cap to ensure proper identification. Remove the cap and bearing inserts.
- Remove the cylinder head.
- Remove the ridge from the top of the sleeve with a ridge reamer.
- Using a hardwood block, drive the piston up and out of the block.
PISTON RING & WRIST PIN REMOVAL
See Figures 8, 9 and 10
All of the gasoline engines covered in this guide utilize pressed-in wrist pins, which can only be removed by an arbor press. The diesel piston pins are removed in the same way, only the pistons are heated before the wrist pins are pressed out.
A piston ring expander is necessary for removing the piston rings without damaging them; any other method (screwdriver blades, pliers, etc.) usually results in the rings being bent, scratched or distorted, or the piston itself being damaged. When the rings are removed, clean the ring 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.
Inspect the pistons for scuffing, scoring, cracks, pitting, or excessive ring groove wear. If these are evident, the piston must be replaced.
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%) to the piston pin, 2 1 / 2 " (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 hones), finish honing is all that is necessary. If the clearance is excessive, try to obtain a slightly larger piston to bring clearance to within specifications. If this is not possible, obtain the first oversize piston and hone (or if necessary, bore) the cylinder to size. Generally, if the cylinder bore is tapered 0.005" (0.127mm) or more or is out-of-round 0.003" (0.076mm) or more, it is advisable to rebore for the smallest possible oversize piston and rings.
After measuring, mark pistons with a felt tip pen for reference and for assembly.
Cylinder honing and/or boring should be performed by a reputable, professional mechanic with the proper equipment. In some cases, clean-up honing can be done with the cylinder block in the car, but most excessive honing and all cylinder boring must be done with the block stripped and removed from the car.
Before honing the diesel cylinders, the piston oil cooling jets must be removed. This procedure should be handled by a diesel specialist, as special tools are needed. Jets cannot be reused; new jets should be fitted.
MEASURING THE OLD PISTONS
See Figures 11 and 12
Check used piston-to-cylinder bore clearance as follows:
- Measure the cylinder bore diameter with a telescope gauge.
- Measure the piston diameter. 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
- 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 0.254mm [0.010"] oversize).
See Figures 13, 14, 15 and 16
- 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, 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 RING INSTALLATION
See Figure 17
Piston ring end-gap should be checked while the rings are removed from the pistons. Incorrect end-gap indicates that the wrong size rings are being used; ring breakage could occur.
Compress the piston rings to be used in a cylinder, one at a time, into that cylinder. Squirt clean oil into the cylinder, so that the rings and the top 2" (51mm) of cylinder wall are coated. Using an inverted piston, press the rings approximately 1" (25mm) below the deck of the block (on diesels, measure ring gap clearance with the ring positioned at the bottom of ring travel in the bore). Measure the ring end-gap with the feeler gauge, and compare to the Ring Gap chart in this guide. Carefully pull the ring out of the cylinder and file the ends squarely with a fine file to obtain the proper clearance.Side Clearance Check
See Figures 18 through 24
Check the pistons to see that the ring grooves and oil return holes have been properly cleaned. Slide a piston ring into its groove, and check the side clearance with a feeler gauge. On gasoline engines, make sure you insert the gauge between the ring and its lower land (lower edge of the groove), because any wear that occurs forms a step at the inner portion of the lower land. On diesels, insert the gauge between the ring and the upper land. If the piston grooves have worn to the extend that relatively high steps exist on the lower land, the piston grooves have worn to the extent that relatively high steps exist on the lower land, the piston should be replaced, because these will interfere with the operation of the new rings and ring clearance will be excessive. Piston rings are not furnished in oversize widths to compensate for ring groove wear.
Install the rings on the piston, lowest ring first, using a piston ring expander. There is a high risk of breaking or distorting the rings, or scratching the piston, if the rings are installed by hand or other means.
Position the rings on the piston as illustrated; spacing of the various piston ring gaps is crucial to proper oil retention and even cylinder wear. When installing new rings, refer to the installation diagram furnished with the new parts.
Install the connecting rod to the piston making sure piston installation notches and any marks on the rod are in proper relation to one another. Lubricate the wrist pin with clean engine oil and install the pin into the rod and piston assembly by using an arbor press as required. Install the wrist pin snaprings if equipped, and rotate them in their grooves to make sure they are seated. To install the piston and rod assemblies:
- Make sure the connecting rod big bearings (including end cap) are of the correct size and properly installed.
- Fit rubber hoses over the connecting rod bolt to protect the crankshaft journals, as in the Piston Removal procedure. Coat the rod bearings with clean oil.
- Using the proper ring compressor, insert the piston assembly into the cylinder so that the notch in the top of the piston faces the front of the engine (this assumes that the dimple(s) or other markings on the connecting rods are in correct relation to the piston notch(s)).
- From beneath the engine, coat each crank journal with clean oil. Pull the connecting rod, with the bearing shell in place, into position against the crank journal.
- Remove the rubber hoses. Install the bearing cap and cap nuts and torque to specification.
When more than one rod and piston assembly is being installed, the connecting rod cap attaching nuts should only be tightened enough to keep each rod in position until all have been installed. This will ease the installation of the remaining piston assemblies.
- Check the clearance between the sides of the connecting rods and the crankshaft using a feeler gauge. Spread the rods slightly with a screwdriver to insert the gauge. If clearance is below the minimum tolerance, the rod may be machined to provide adequate clearance. If clearance is excessive, substitute an unworn rod, and recheck. If clearance is still outside specifications, the crankshaft must be welded and reground, or replaced.
- Replace the oil pump if removed, and the oil pan.
- Install the cylinder head(s) and intake manifold.