REMOVAL & INSTALLATION
See Figures 1, 2 and 3
- Disconnect the negative battery cable. Drain the engine oil and remove the engine from the vehicle. Mount the engine on a work stand in a suitable working area. Invert the engine, so the oil pan is facing up.
- Remove the engine front (timing) cover.
- Remove the timing chain and gears.
- Remove the oil pan.
- Remove the oil pump.
- Stamp the cylinder number on the machined surfaces of the bolt bosses of the connecting rods and caps for identification when reinstalling. If the pistons are to be removed eventually from the connecting rod, mark the cylinder number on the pistons with silver paint or felt-tip pen for proper cylinder identification and cap-to-rod location.
- Remove the connecting rod caps. Install lengths of rubber hose on each of the connecting rod bolts, to protect the crank journals when the crank is removed.
- Mark the main bearing caps with a number punch or punch so that they can be reinstalled in their original positions.
- Remove all main bearing caps.
- Note the position of the keyway in the crankshaft so it can be installed in the same position.
- Install rubber bands between a bolt on each connecting rod and oil pan bolts that have been reinstalled in the block. This will keep the rods from banging on the block when the crank is removed.
- Carefully lift the crankshaft out of the block. The rods will pivot to the center of the engine when the crank is removed.
- When main bearing clearance has been checked, bearings examined and/or replaced, the crankshaft can be installed. Thoroughly clean the upper and lower bearing surfaces, and lube them with clean engine oil. Install the crankshaft and main bearing caps.
- Dip all main bearing cap bolts in clean oil, and torque all main bearing caps, excluding the thrust bearing cap, to specifications. Tighten the thrust bearing bolts finger tight. To align the thrust bearing, pry the crankshaft the extent of its axial travel several times, holding the last movement toward the front of the engine. Add thrust washers if required for proper alignment. Torque the thrust bearing cap to specifications.
- To check crankshaft end play, pry the crankshaft to the extreme rear of its axial travel, then to the extreme front of its travel. Using a feeler gauge, measure the end play at the front of the rear main bearing. End play may also be measured at the thrust bearing. Install a new rear main bearing oil seal in the cylinder block and main bearing cap. Continue to reassemble the engine.
On the 1986 and 1987 231 and 307 cu. in. engines, it is necessary to line up the rear main bearing and crankshaft thrust surfaces. Torque all main caps to specification except the one at the rear. Torque the rear main cap to 10-12 ft. lbs. (14-16 Nm). Using a lead hammer, tap the end of the crankshaft first backward and then forward. Now, retorque all caps to specification.
Like connecting rod bearings, the crankshaft main bearings are shell type inserts that do not utilize shims and cannot be adjusted. The bearings are available in various standard and undersizes; if main bearing clearance is found to be out of specification, a new bearing (both upper and lower halves) is required.
Factory undersized crankshafts are marked, sometimes with a 9 and/or a large spot of light green paint; the bearing caps also will have the paint on each side of the undersized journal.
Generally, the lower half of the bearing shell (except No. 1 bearing) shows greater wear and fatigue. If the lower half only shows the effects of normal wear (no heavy scoring or discoloration), it can usually be assumed that the upper half is also in good shape; conversely, if the lower half is heavily worn or damaged, both halves should be replaced. Never replace one bearing half without replacing the other.
Main bearing clearance can be checked with the crankshaft in the vehicle and with the engine out of the vehicle. If the engine block is still in the vehicle, the crankshaft should be supported both front and rear (by the damper and to remove clearance from the upper bearing. Total clearance can then be measured between the lower bearing and journal. If the block has been removed from the vehicle, and is inverted, the crank will rest on the upper bearings and the total clearance can be measured between the lower bearing and journal. Clearance is checked in the same manner as the connecting rod bearings, with Plastigage®.
Crankshaft bearing caps and bearing shells should NEVER be filed flush with the cap-to-block mating surface to adjust for wear in the old bearings. Always install new bearings. The low cost of new bearings outweighs the aggravation of having to do the job twice because of failed bearings.
- If the crankshaft has been removed, install it (block removed from vehicle). If the block is still in the vehicle, remove the oil pan and oil pump. Starting with the rear bearing cap, remove the cap and wipe all oil from the crank journal and bearing cap.
- In order to check bearing clearance, the crankshaft must rest against the upper bearings. If the engine is out of the vehicle, turning the block upside down will take care of this requirement. If the engine is in the vehicle, the crankshaft must be supported at either end so that it rests against the upper bearings and all clearance is present at the lower bearing. Place a strip of Plastigage® the full width of the bearing, (parallel to the crankshaft), on the journal.
- Install the bearing cap and evenly torque the cap bolts to specification.
- Remove the bearing cap. The flattened Plastigage® will be sticking to either the bearing shell or the crank journal.
- Use the graduated scale on the Plastigage® envelope to measure the material at its widest point.
If the flattened Plastigage® tapers toward the middle or ends, there is a difference in clearance indicating the bearing or journal has a taper, low spot or other irregularity. If this is indicated, measure the crank journal with a micrometer.
- If bearing clearance is within specifications, the bearing insert is in good shape. Replace the insert if the clearance is not within specifications. Always replace both upper and lower inserts as a unit.
- Standard, 0.001 in. (0.0254mm) or 0.002 in. (0.0508mm) undersize bearings should produce the proper clearance. If these sizes still produce too sloppy a fit, the crankshaft must be reground for use with the next undersize bearing. Recheck all clearances after installing new bearings.
- Replace the rest of the bearings in the same manner. After all bearings have been checked, rotate the crankshaft to make sure there is no excessive drag. When checking the No. 1 main bearing, loosen the accessory drive belts (engine in vehicle) to prevent a tapered reading with the Plastigage®.
See Figures 4 and 5Engine Out of vehicle
- Remove and inspect the crankshaft.
- Remove the main bearings from the bearing saddles in the cylinder block and main bearing caps.
- Coat the bearing surfaces of the new, correct size main bearings with high quality assembly lube and install them in the bearing saddles in the block and in the main bearing caps. Make sure the tabs in the bearing insert align with the notch in the block and bearing cap.
- Install the crankshaft.
- With the oil pan, oil pump and spark plugs removed, remove the cap from the main bearing needing replacement and remove the bearing from the cap.
- Make a bearing roll-out pin, using a bent cotter pin. Install the end of the pin in the oil hole in the crankshaft journal.
- Rotate the crankshaft clockwise as viewed from the front of the engine. This will roll the upper bearing out of the block.
Turn the crankshaft in the opposite direction of the bearing insert tab. The bearing insert will only turn on way.
- Lube the new upper bearing with clean engine oil and insert the plain (unnotched) end between the crankshaft and the indented or notched side of the block. Roll the bearing into place, making sure that the oil holes are aligned. Remove the roll pin from the oil hole.
- Lube the new lower bearing and install the main bearing cap. Install the main bearing cap, making sure it is positioned in proper direction with the matchmarks in alignment.
- Torque the main bearing cap bolts to specification.
See crankshaft removal and installation for thrust bearing alignment.