See Figures 1 and 2
- Remove the engine from the vehicle. Mount it on a stand which allows the engine to be rotated for easy access.
- If not already done, remove the transmission from the engine.
- Remove the cylinder head and the front cover, timing belt or chains and sprockets as described earlier in this section.
- Remove the oil pan (if not removed already) and pick-up screen.
- Remove the oil pump.
- Remove the flywheel and pilot bearing or torque converter drive plate, adapter plate and crankshaft bushing.
- Remove the bell housing cover and rear plate, on those models so equipped.
- Remove the rear main seal housing and seal.
- Check the crankshaft end-play. Shift the crankshaft as far to the rear as possible. Install a dial indicator on the front of the engine with the stem directly on the front of the crankshaft. Zero the indicator and use a small pry bar to shift the crankshaft forward as far as it will go. The amount of motion will show on the dial indicator; read the figure and compare with specifications. Excess end-play is a sign of wear.
It's best to check the end-play with the engine in its upright (normal) position.
- Invert the engine, and remove the connecting rod caps, keeping them in exact order. Loosen the bolts slowly and evenly. It is recommended that each cap be marked with its cylinder number before disassembly.
- Remove the main bearing caps, keeping them in order. The caps are marked with arrows indicating the front of the engine, and are numbered in order from front to rear.
- Once all the bearing caps are removed, the crankshaft may be removed if necessary.
- Clean the crankshaft and bearing surfaces with a parts solvent. If necessary, remove the bearing shells from the caps, block and connecting rods in order to soak them. Note or diagram their positions and keep them in exact order at all times. Once used, bearing shells are NOT interchangeable and must be reinstalled in their original location.
INSPECTION AND CLEANING
See Figures 3, 4 and 5
- Inspect the crankshaft journals for scuffing, grooving or scoring. If crankshaft wear is uneven, the crankshaft should be turned on a lathe by a competent machine shop. Each journal will be undersize and new, undersize (thicker) bearings must be installed.
- Make sure all the oil passages are clean, if necessary cleaning them with solvent and a stiff bristle brush.
- It is recommended that crankpins and main bearing journals be measured with a micrometer to check for wear, out-of-roundness, and taper. Out-of-round is checked by measuring the journal across 2 diameters which are 90° apart (north-south and east-west) and comparing the two readings. The difference between the two readings gives the out-of-round specification.Taper is determined by measuring each journal at each end and comparing the numbers. If one reading is larger than the other, the journal tapers from large to small.
- Inspect the bearing surfaces for burning, grooving, or scoring of any kind. Any but the slightest scratches disqualify a bearing from reuse; if there is any doubt, replace the bearings. (A good rule of thumb is to replace the bearing every time they are disassembled.) If the end-play, as measured above, is excessive, new bearings must be installed.
If new bearings fail to correct end-play problems, the crankshaft will have to be machined undersize and different bearings installed.
See Figures 6, 7, 8, 9, 10 and 11
- Once the crankshaft has been cleaned, inspected or machined, the bearing clearance must be checked. this must be done in all cases, including reuse of old bearings or installation of thicker bearings. The bearing clearance (or oil clearance) is a critical dimension and must be proper before final assembly.
- Install the crankshaft into the block (the block is inverted) and make sure all bearing surfaces and journals are clean and dry. Cut pieces of plastic measuring media (such as Plastigage® or similar product) to fit the width of the bearing. Lay the piece widthwise across the journal. The insert must not rest on top of oil holes and the bearing shell that clamps against it must not be a grooved one.
- Install and tighten all rod and main bearing caps to specifications. Do NOT turn the crankshaft. Remove the caps and read the width of the measuring media at the widest point. This is done by comparing the width at its widest point to lines on the scale included with the package. If working on a V6 engine, install the bearing cap to the engine block as shown in the illustration. Tighten the bearing cap bolts to the specified torque in the sequence shown.
- If the bearing clearance is to specification, old bearings may be re-used if otherwise in good condition. In cases of moderate, regular wear, it may be feasible to replace the bearings with new ones of original size and avoid machining the crankshaft, provided this gives the specified clearance.
- If there is any question about the wear pattern or the ability of the new bearing shells to provide correct clearance, it is advisable to have the crankshaft machined and install matching bearings.
- Before final assembly, all bearing surfaces must be thoroughly lubricated with clean engine oil. Make sure the main bearings have the oil holes lined up and that the upper shells for bearings 1, 2, 4, and 5 have grooves so that oil will pass to the connecting rod journals.The center main bearings, both top and bottom, are groove-less but include thrust bearing surfaces (flanges). Make sure connecting rod bearings have the notches in the bearing and cap together. Make sure all main bearing caps are installed in their original positions and directions. Main bearing caps are numbered in order from front to rear and have an arrow indicating the front (crankshaft pulley) end of the engine. Bearing cap bolts should be tightened evenly in 3 stages to specification. Work in sequence, starting with the center main bearing cap, then moving to No. 2, No. 4, front, and rear caps.
- Reinstall the crankshaft seals, the oil pick-up screen and oil pan as soon as possible. Even if other work is to performed on the engine, the seals and pan will serve to protect the crankshaft, rods and bearings from dirt and impact damage.