See Figures 1 through 5
These procedures may be performed with the engine in the car. If additional overhaul work is to be performed, it will be easier if the engine is removed and mounted on an engine stand. Most stands allow the block to be rotated, giving easy access to both the top and bottom. These procedures require certain hand tools which may not be in your tool box. A cylinder ridge reamer, a numbered punch set, piston ring expander, snapring tools and piston installation tool (ring compressor) are all necessary for correct piston and rod repair. These tools are commonly available from retail tool suppliers; you may be able to rent them from larger automotive supply houses.
- Remove the cylinder head.
- Elevate and safely support the vehicle on jackstands.
- Drain the engine oil.
- Remove any splash shield or rock guards which are in the way and remove the oil pan.
- Using a numbered punch set, mark the cylinder number on each piston rod and bearing cap. Do this BEFORE loosening any bolts.
- Loosen and remove the rod cap nuts and the rod caps. It will probably be necessary to tap the caps loose; do so with a small plastic mallet or other soft-faced tool. Keep the bearing insert with the cap when it is removed.
- Use short pieces of hose to cover the bolt threads; this protects the bolt, the crankshaft and the cylinder walls during removal.
- One piston will be at the lowest point in its cylinder. Cover the top of this piston with a rag. Examine the top area of the cylinder with your fingers, looking for a noticeable ridge around the cylinder. If any ridge is felt, it must be carefully removed by using the ridge reamer. Work with extreme care to avoid cutting too deeply.When the ridge is removed, carefully remove the rag and ALL the shavings from the cylinder. No metal cuttings may remain in the cylinder or the wall will be damaged when the piston is removed. A small magnet or an oil soaked rag can be helpful in removing the fine shavings.
- After the cylinder is de-ridged, squirt a liberal coating of engine oil onto the cylinder walls until evenly coated. Carefully push the piston and rod assembly upwards from the bottom by using a wooden hammer handle on the bottom of the connecting rod.
- The next lowest piston should be gently pushed downwards from above. This will cause the crankshaft to turn and relocate the other pistons as well. When the piston is in its lowest position, repeat the steps used for the first piston. Repeat the procedure for each of the remaining pistons.
- When all the pistons are removed, clean the block and cylinder walls thoroughly with solvent.
CLEANING AND INSPECTION
See Figures 6 through 10Pistons
With the pistons removed from the engine, use a ring removing tool (ring expander) to remove the rings. Keep the rings labeled and stored by piston number. Clearly label the pistons by number so that they do not get interchanged.
Clean the carbon from the piston top and sides with a stiff bristle brush and cleaning solvent. Do not use a wire brush for cleaning.
Clean the ring grooves (lands) either with a specially designed tool or with a piece of a broken piston ring. Remove all the carbon from the grooves and make sure that the groove shape (profile) is square all the way around the piston. When all the lands have been cleaned, again bathe the piston in solvent and clean the lands with the bristle brush.
Before any measurements are begun, visually examine the piston (a magnifying glass can be handy) for any signs of cracks-particularly in the skirt area-or scratches in the metal. Anything other than light surface scoring disqualifies the piston from further use. The metal will become unevenly heated and the piston may break apart during use.
Hold the piston and rod upright and attempt to move the piston back and forth along the piston pin (wrist pin). There should be NO motion in this axis. If there is, replace the piston and wrist pin.
Accurately measure the cylinder bore diameter in two dimensions (thrust and axial, or if you prefer, left-right and fore-aft) and in three locations (upper, middle and bottom) within the cylinder. That's six measurements in each bore; record them in order.
Having recorded the bore measurements, now measure the piston diameter. Do this with a micrometer at right angles to the piston pin. The location at which the piston is measured varies by engine type:
The piston-to-cylinder wall clearance (sometimes called oil clearance) is determined by subtracting the piston diameter from the measured diameter of its respective cylinder. The difference will be in thousandths or ten-thousandths of an inch. Compare this number to the Piston and Ring Specifications Chart in this section. Excess clearance may indicate the need for either new pistons or block reboring.
The connecting rods must be free from wear, cracking and bending. Visually examine the rod, particularly at its upper and lower ends. Look for any sign of metal stretching or wear. The piston pin should fit cleanly and tightly through the upper end, allowing no side-play or wobble. The bottom end should also be an exact 1 / 2 circle, with no deformity of shape. The bolts must be firmly mounted and parallel.
The rods may be taken to a machine shop for exact measurement of twist or bend. This is easier and cheaper than purchasing a seldom used rod-alignment tool.
See Figure 11
Most inspection and service work on the cylinder block should be handled by a machinist or professional engine rebuilding shop. Included in this work are bearing alignment checks, line boring, deck resurfacing, hot-tanking and cylinder block boring. Any or all of this work requires that the block be completely stripped of all components and transported to the shop. A block that has been checked and properly serviced will last much longer than one whose owner cut corners during a repair.
Cylinder de-glazing (honing) can be performed by the owner/mechanic who is careful and takes time to be accurate. The cylinder bores become glazed during normal operation of the engine as the rings ride up and down constantly. This shiny glaze must be removed in order for a new set of piston rings to seat properly.
Cylinder hones are available at most auto tool stores and parts jobbers. Install the hone into the chuck of a variable speed drill (preferred in place of a constant speed drill). With the piston, rod and crankshaft assemblies removed from the block, insert the hone into the cylinder. If the crankshaft is not being removed from the block, cover it completely with oil soaked rags to prevent grit from collecting on it.
Make sure the drill and hone are kept square to the cylinder bore during the entire honing procedure.
Start the drill and move the hone up and down in the cylinder at a rate which will produce approximately a 60 degree crosshatch pattern. DO NOT extend the hone below the bottom of the cylinder bore. After the crosshatched pattern is established, remove the hone.
Wash the cylinder with a solution of detergent and water to remove the honing and cylinder grit. Wipe the bores out several times with a clean rag soaked in fresh engine oil. If applicable, carefully remove the rags from the crankshaft and check closely to see that NO grit has found its way onto the crankshaft.
PISTON PIN REPLACEMENT
The piston and pin are a matched set and must be kept together. Label everything and store parts in identified containers.
- Remove the pistons from the engine and remove the rings from the pistons.
- Support the piston and rod on its side in a press. Make certain the piston is square to the motion of the press and that the rod is completely supported with blocks. Leave open space below the piston for the pin to emerge.
- Line up the press and insert a brass rod of a slightly smaller diameter as the piston pin. It is important that the rod press evenly on the entire face of the pin, but not on the piston itself.
- Using smooth and controlled motion, press the pin free of the piston. Do not use sudden or jerky motions; the piston may crack.
- When reassembling, identify the front of the piston by its small dot or cavity on the top. Identify the front of the piston rod by the small mark cast into one face of the rod. Make sure the marks on the piston and rod are both facing the same direction. Also insure that the correct piston pin is to be reinstalled-they are not interchangeable.
- Insert the piston under the press. Position the rod and support it. Coat the piston pin with clean oil and press it into place, using the same press set-up as removal.
PISTON RING REPLACEMENT
See Figures 12 through 16
Although a piston ring can be reused if in good condition and carefully removed, it is recommended that the rings be replaced with new ones any time they are removed from the pistons.
A piston ring expander is necessary for removing piston rings without damaging them; any other method (screwdriver blades, pliers, etc.) usually results in the rings becoming bent, scratched or broken. When the rings are removed, clean the grooves thoroughly with a bristle brush and solvent. Make sure that all traces of carbon and varnish are removed.
Check the piston condition and diameter following procedures outlined earlier in this section. Piston ring end-gap should be checked when the rings are removed from the pistons. Incorrect end-gap indicates that the wrong size rings are being used; ring breakage could occur.
Squirt some clean oil into the cylinder so that the top 50-75mm (2-3 in.) of the wall is covered. Gently compress one of the rings to be used and insert it into the cylinder. Use an upside-down piston and push the ring down a little beyond the bottom of piston ring travel. Using the piston to push the ring keeps the ring square in the cylinder; if it is crooked, the next measurement may be inaccurate.
Using a feeler gauge, measure the end-gap in the ring and compare it to the Piston and Ring Specifications chart in this section. If the gap is excessive, either the ring is incorrect or the cylinder walls are worn beyond acceptable limits. If the measurement is too tight, the ends of the ring may be filed to enlarge the gap after the ring is removed form the cylinder. If filing is needed, make certain that the ends are kept square and that a fine file is used.
Check the pistons to see that the ring grooves and oil return holes have been properly cleaned. Slide each piston ring into its groove and check the side clearance with a feeler gauge. Make sure you insert the feeler gauge between the ring and its lower edge; any wear that develops forms a step at the inner portion of the lower land. If the piston grooves have worn to the extent that fairly high steps exist on the lower land, the piston must be replaced. Rings are not sold in oversize thicknesses to compensate for ring groove wear.
Using the ring expander, install the rings on the piston, lowest ring first. There is a high risk of ring breakage or piston damage if the rings are installed by hand or without the expander. The correct spacing of the ring end-gaps is critical to oil control. No two gaps should align, they should be evenly spaced around the piston. Once the rings are installed, the pistons must be handled carefully and protected from dirt and impact.
ROD BEARING REPLACEMENT
See Figures 17, 18 and 19
Connecting rod bearings on all engines consist of two halves or shells which are not interchangeable in the rod and cap. When the shells are in position, the ends extend slightly beyond the rod and cap surfaces so that when the bolts are tightened, the shells will be clamped tightly in place. This insures a positive seating and prevents turning. A small tang holds the shells in place within the cap and rod housings.
The ends of the bearing shells must never be filed flush with the mating surface of the rod or cap.
If a rod becomes noisy or is worn so that its clearance on the crankshaft is out of specification, a new bearing of the correct undersize must be selected and installed. There is no provision for adjustment. Under no circumstances should the rod end or cap be filed to compensate for wear, nor should shims of any type be used.
Inspect the rod bearings while the rods are out of the engine. If the shells are scored or show flaking they should be replaced. ANY scoring or ridge on the crankshaft means the crankshaft must be replaced. Because of the metallurgy in the crankshaft, welding and regrinding the crankshaft is not recommended. The bearing faces of the crank may not be restored to their original condition or attempts may cause premature bearing wear and possible failure.
Replacement bearings are available in three standard sizes marked either 1, 2 or 3 on the bearing shell and possibly on the rod cap. Do not confuse the mark on the bearing cap with the cylinder number. It is quite possible that No. 3 piston rod contains a number 1 size bearing. The rod cap may have a 1 marked on it. (You should have stamped a 3 or other identifying code on both halves of the rod before disassembly.)
Measuring the clearance between the connecting rod bearings and the crankshaft (oil clearance) is done with a plastic measuring material such as Plastigage® or similar product.
- Remove the rod cap with the bearing shell. Completely clean the cap, bearing shells and the journal on the crankshaft. Blow any oil from the oil hole in the crank. The plastic measuring material is soluble in oil and will begin to dissolve if the area is not totally free of oil.
- Place a piece of the measuring material lengthwise along the bottom center of the lower bearing shell. Install the cap and shell, then tighten the bolts in three passes to specifications.
Do not turn the crankshaft with the measuring material installed.
- Remove the bearing cap with the shell. The flattened plastic material will be found sticking to either the bearing shell or the crank journal. DO NOT remove it yet.
- Use the scale printed on the packaging for the measuring material to measure the flattened plastic at its widest point. The number within the scale which is closest to the width of the plastic indicates the bearing clearance in thousandths of an inch.
- Check the specifications chart for the proper clearance. If there is any measurement approaching the maximum acceptable value, replace the bearing.
- When the correct bearing is determined, clean off the gauging material, oil the bearing thoroughly on its working face and install it in the cap. Install the other half of the bearing into the rod end and attach the cap to the rod. Tighten the nuts evenly, in three passes to specifications.
- With the proper bearing installed and the nuts properly tightened, it should be possible to move the connecting rod back and forth a bit on the crankshaft. If the rod cannot be moved, either the bearing is too small or the rod is misaligned.
See Figures 20, 21 and 22
- When ready for reassembly, remember that all the pistons, rods and caps must be reinstalled in the correct cylinder. Make certain that all labels and stamped numbers are present and legible. Double check the piston rings; make certain that the ring gaps DO NOT line up, but are evenly spaced around the piston at about 120 degree intervals. Double check the bearing insert at the bottom of the rod for proper mounting. Reinstall the protective rubber hose pieces on the bolts.
- Liberally coat the cylinder walls and the crankshaft journals with clean, fresh engine oil. Also apply oil to the bearing surfaces on the connecting rod and the cap.
- Identify the "Front'' mark on each piston and rod and position the piston loosely in its cylinder with the marks facing the front (pulley end) of the motor.
- Install the ring compressor (piston installation tool) around one piston and tighten it gently until the rings are compressed almost completely.
- Gently push down on the piston top with a wooden hammer handle or similar soft-faced tool and drive the piston into the cylinder bore. Once all three rings are within the bore, the piston will move with some ease.
If any resistance or binding is encountered during the installation, DO NOT apply force. Tighten or adjust the ring compressor and/or reposition the piston. Brute force will break the ring(s) or damage the piston.
- From underneath, pull the connecting rod into place on the crankshaft. Remove the rubber hoses from the bolts. Check the rod cap to confirm that the bearing is present and correctly mounted, then install the rod cap (observing the correct number and position) and its nuts. Leaving the nuts finger-tight will make installation of the remaining pistons and rods easier.
- Assemble the remaining pistons in the same fashion.
- With all the pistons installed and the bearing caps secured finger-tight, the retaining nuts may be tightened to their final setting. For each pair of nuts, make three passes alternating between the two nuts on any given rod cap. The intent is to draw each cap up to the crank straight and under even pressure at the nuts.
- Turn the crankshaft through several clockwise rotations, making sure everything moves smoothly and there is no binding. With the piston rods connected, the crank may be stiff to turn-try to turn it in a smooth continuous motion so that any binding or stiff spots may be felt.
- Reinstall the oil pan. Even if the engine is to remain apart for other repairs, install the oil pan to protect the bottom end and tighten the bolts to the correct specification-this eliminates one easily overlooked mistake during future reassembly.
- If the engine is to remain apart for other repairs, pack the cylinders with crumpled newspaper or clean rags (to keep out dust and grit) and cover the top of the motor with a large rag. If the engine is on a stand, the whole block can be protected with a large plastic trash bag.
- If no further work is to be performed, continue reassembly by installing the head, timing belt, etc.
- When the engine is restarted after reassembly, the exhaust will be very smoky as the oil within the cylinders burns off. This is normal; the smoke should clear quickly during warm up. Depending on the condition of the spark plugs, it may be wise to check for any oil fouling after the engine is shut off.