The most critical maintenance operation is the replacement of the crankshaft main bearings. These bearings are of the precision insert design and do not require adjustment through shims. They are offered in undersizes of 0.001 in., 0.002 in., 0.009 in., 0.010 in., 0.020 in., and 0.030 in., depending on the engine.
Despite the advent of these inserts and accompanying precision machine work, it does happen that sizing mistakes are made and no crankshaft should be installed in a block without checking clearances. One of the simplest means of doing so is to use Plastigage®. This is a wax-like plastic material that is formed into precision threads. It will compress evenly between two surfaces, without damage, and when measured, will indicate the actual clearance.
It is easiest to check bearing clearance with the engine removed from the vehicle and the block inverted. This ensures that the crank is resting against the upper bearing shells. If Plastigage® is to be used on an engine still in the vehicle, it will be necessary to support the crankshaft at both ends so that clearance between the crankshaft and the upper bearing shells is eliminated.
REMOVAL & INSTALLATION
See Figures 1, 2, 3 and 4
- Drain the crankcase oil and remove the engine from the truck.
- Remove the flywheel and mount the engine on a workstand in a suitable working area. Invert the engine, so the oil pan is facing up.
If the cylinder heads are not being removed, the spark plugs should be removed in order to release engine compression and allow for easier rotation of the crankshaft when necessary.
- Remove the engine front (timing) cover.
- Align the timing marks, then remove the timing chain and gears.
After removing the timing gear or sprocket from the crankshaft, be sure to remove the Woodruff key from the crankshaft.
- Remove the oil pan.
- If necessary, remove the oil pump assembly.
- Inspect the connecting rods and bearing caps for identification marks (numbers). If there are none, 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 nuts and caps, then store them in the order of removal. Place short pieces of rubber hose on the connecting rod studs to prevent damaging the crankshaft bearing surfaces.
- Check the main bearing caps for identification marks (if not identified, mark them). Remove the main bearing caps and store them in order, for reassembly purposes; the caps must be reinstalled in their original position.
- If equipped, remove the 1-piece rear main seal retainer from the engine.
- Install rubber bands between a bolt on each connecting rod and oil pan bolts that have been reinstalled in the block (see illustration). 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.
- Clean and inspect all parts for damage. Repair or replace, as necessary.
- Install new bearing shell inserts and check the bearing clearances.
If necessary, deliver the crankshaft to an automotive machine shop, have the crankshaft journals ground and new bearing shells matched.
- Lubricate all of the parts and oil seals with clean engine oil.
- Using a feeler gauge and a medium prybar, move the crankshaft forward-and-rearward. Check the crankshaft end-play by inserting a feeler gauge between the crankshaft and the thrust bearing shell. An alternate method is to use a dial indicator at the crankshaft snout. Install the indicator, move the crankshaft rearward, zero the indicator and then move the crankshaft forward. the dial indicator will read the end-play. Thrust bearing location varies with the engine.
- Tighten main bearing caps (in three steps) to specification. Use Plastigage® or equivalent to check for proper bearing clearance.
- Remove the rubber hoses from the studs. Install the bearing cap (with bearing shell) onto the connecting rod and the cap nuts. Torque the connecting rod cap nuts (in stages) to specification. Use Plastigage® or equivalent to check for proper bearing clearance.
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 connecting rod side clearance by inserting a feeler gauge between the side of the rod and the crankshaft. If not within specification, repair as necessary.
- If necessary, install the pump assembly.
- Install the oil pan.
- Make sure the Woodruff key is installed in the end of the crankshaft, then install the timing chain and gears.
- Install the engine front (timing) cover.
- Remove the engine from the workstand, then install the flywheel.
- Refill the crankcase and install the engine to the truck.
CLEANING AND INSPECTION
See Figures 5, 6, 7, 8 and 9
- Clean the crankshaft with solvent and a brush. Clean the oil passages with a suitable brush, then blow them out with compressed air.
- Inspect the crankshaft for obvious damage or wear. Check the main and connecting rod journals for cracks, scratches, grooves or scores. Inspect the crankshaft oil seal surface for nicks, sharp edges or burrs that could damage the oil seal or cause premature seal wear.
- If the crankshaft passes a visual inspection, check journal run-out using a dial indicator. Support the crankshaft in V-blocks and check the run-out. Compare to specifications.
- Measure the main and connecting rod journals for wear, out-of-roundness or taper, using a micrometer. Measure in at least 4 places around each journal and compare your findings with the journal diameter specifications.
- If the crankshaft fails any inspection for wear or damage, it must be reground or replaced.
Like connecting rod big-end 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 excessive, 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!
See Figure 10
The following procedure requires the use of Plastigage® or a micrometer set consisting of inside and outside micrometers, and a dial indicator.
- Inspect the bearings for scoring, chipping or other wear.
- Inspect the crankshaft journals as detailed in the Cleaning and Inspection procedure.
- If the crankshaft journals appear usable, clean them and the bearing shells until they are completely free of oil. Blow any oil from the oil hole in the crankshaft.
To check the crankshaft/rod bearing clearances using a micrometer, perform the following procedures:
- Set the crankshaft on V-blocks. Using a dial indicator set on the center bearing journal, check the crankshaft run-out. Repair or replace the crankshaft if out of specification.
- Using an outside micrometer, measure the crankshaft bearing journals for diameter and out-of-round conditions; if necessary, regrind the bearing journals.
- Install the bearings and caps and torque the nuts/bolts to specifications. Using an inside micrometer, check the bearing bores in the engine block. If out of specification, regrind the bearing bores to the next largest oversize.
- The difference between the two readings is the bearing clearance. If out of specification, inspect for the cause and repair as necessary.
- To inspect the main bearing surfaces, using the Plastigage® method, perform the following procedures:
Plastigage® is soluble in oil. The journal surfaces and bearing shells must be completely free of oil to get an accurate reading with Plastigage®.
- Place a strip of Plastigage® lengthwise along the bottom center of the lower bearing shell, then install the cap with the shell and torque the connecting rod nuts or main cap bolts to specification.
When the Plastigage® material is installed on the bearing surfaces, DO NOT rotate the crankshaft.
- Remove the bearing cap with the shell. The flattened Plastigage® will either be sticking to the bearing shell or the crankshaft journal.
- Using the printed scale on the Plastigage® package, measure the flattened Plastigage® at its widest point. The number on the scale that most closely corresponds to the width of the Plastigage® indicates the bearing clearance in thousandths of an inch or hundredths of a millimeter.
- Compare your findings with the bearing clearance specification. If the bearing clearance is excessive, the bearing must be replaced or the crankshaft must be ground and the bearing replaced.
Bearing shell sets over standard size are available to correct excessive bearing clearance.
- After clearance measuring is completed, be sure to remove the Plastigage® from the crankshaft and/or bearing shell.
- For final bearing shell installation, make sure the connecting rod and rod cap and/or cylinder block and main cap bearing saddles are clean and free of nicks or burrs. Install the bearing shells in the bearing saddles, making sure the bearing shell tangs are seated in the notches.
Be careful when handling any plain bearings. Your hands and the working area should be clean. Dirt is easily embedded in the bearing surface and the bearings are easily scratched or damaged.