REMOVAL & INSTALLATION
See Figure 1
- Remove the engine assembly as previously outlined.
- Remove the engine front cover.
- Remove the timing chain and sprockets or 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 from the connecting rod, mark cylinder number on piston with a silver pencil or quick drying paint for proper cylinder identification and cap to rod location.
- Remove the connecting rod caps and install thread protectors.
- Mark the main bearing caps so that they can be reinstalled in their original positions.
- Remove all the main bearing caps. They all must go back to their original locations and they must all face the same direction. Any cap install incorrectly will cause engine damage when reassembled.
- Note position of keyway in crankshaft so it can be installed in the same position.
- Lift crankshaft out of block. Rods will pivot to the center of the engine when the crankshaft is removed.
- Remove both halves of the rear main oil seal if two piece design. If a one piece design, remove the seal.
- Clean all of the oil sludge and carbon deposits. Probe the oil passages for any obstructions.
- Inspect the bearing journals for; cracks, chips, gouges, roughness, grooves, and overheating (discoloration).
- Inspect the corresponding bearing inserts for any imbedded foreign materials, then determine it's source.
- If cracks, burned spots or gouges are found, you must replace the crankshaft.
- Measure the crankshaft journals with a micrometer to determine the correct size rod and main bearings to be used. Whenever a new or reconditioned crankshaft is installed, new connect rod bearings and main bearings should be installed.
- Clean all oil passages in the block (and crankshaft if it is being reused).
A new rear main seal should be installed anytime the crankshaft is removed or replaced. If any engine repair is made, any related seals or gaskets should be replaced. It's not worth the time lost to repeat a repair job due to an old seal or gasket leaking.
- Install sufficient oil pan bolts in the block to align with the connecting rod bolts. Use rubber bands between the bolts to position the connecting rods as required. Connecting rod position can be adjusted by increasing the tension on the rubber bands with additional turns around the pan bolts or thread protectors.
- Position the upper half of main bearings in the block and lubricate with engine oil.
- Position crankshaft keyway in the same position as removed and lower into block. The connecting rods will follow the crank pins into the correct position as the crankshaft is lowered.
- Lubricate the thrust flanges with GM part no. 1050169 lubricant or equivalent. Install caps with lower half of bearings lubricated with engine oil. Lubricate cap bolts with engine oil and install, but do not tighten.
- With a block of wood, bump the shaft in each direction to align thrust flanges of main bearing. After bumping shaft in each direction, wedge the shaft to the front and hold it while tightening the thrust bearing cap bolts.
In order to prevent the possibility of cylinder block and/or main bearing cap damage, the main bearing caps are to be tapped into their cylinder block cavity using a brass or leather mallet before attaching bolts are installed. Do not use attaching bolts to pull main bearing caps into their seat.
- Tighten all main bearing caps to specification.
- Remove the connecting rod bolt thread protectors and lubricate the connecting rod bearings with engine oil.
- Install the connecting rod bearing caps in their original position. Tighten the nuts to specification.
- Complete the installation by reversing the removal steps.
CHECKING BEARING CLEARANCE
- Remove bearing cap and wipe oil from crankshaft journal and outer and inner surfaces of bearing shell.
- Place a piece of plastic gauging material (Plastigage® or equivalent) in the center of bearing. Position the crankshaft in the saddles.
- Reinstall bearing cap and bearing. Place engine oil on cap bolts and install. Tighten bolts to specification.
- Remove bearing cap and determine bearing clearance by comparing the width of the flattened plastic gauging material at its widest point with graduations on the gauging material container. The number within the graduation on the envelope indicates the clearance in millimeters or thousandths of an inch. If the clearance is greater than allowed, REPLACE BOTH BEARING SHELLS AS A SET. Recheck clearance after replacing shells.
Main bearing clearances must be corrected by the use of selective upper and lower shells. To install main bearing shells, proceed as follows:
- Remove the oil pan. On some models, the oil pump may also have to be removed.
- Loosen all main bearing caps.
- Remove bearing cap and remove lower shell.
- Insert a flattened cotter pin or roll out pin in the oil passage hole in the crankshaft in the direction opposite to cranking rotation. The pin will contact the upper shell and roll it out.
- The main bearing journals should be checked for roughness and wear. Slight roughness may be removed with a fine grit polishing cloth saturated with engine oil. Burrs may be removed with a fine oil stone. If the journals are scored or ridged, the crankshaft must be replaced.
- Clean crankshaft journals and bearing caps thoroughly before installing new main bearings.
- Apply lubricant GM part no.1050169 or equivalent to the thrust flanges of bearing shells.
- Place new upper shell on crankshaft journal with locating tang correctly positioned and rotate shaft to turn it into place. Use the cotter pin or roll out pin as during removal.
- Place new bearing shell in bearing cap.
- Install a new oil seal in the rear main bearing cap and block.
- Lubricate the removed or replaced main bearings with engine oil. Lubricate the thrust surface with lubricant GM part no.1050169 or equivalent.
- Lubricate the main bearing cap bolts with engine oil.
In order to prevent the possibility of cylinder block and/or main bearing cap damage, the main bearing caps are to be tapped into their cylinder block cavity using a brass or leather mallet before attaching bolts are installed. Do not use attaching bolts to pull main bearing caps into their seats.
- Tighten the main bearing cap bolts.
The bearings can easily be replaced after the crankshaft is removed. Simply remove the bearing inserts from the saddles and main bearing caps, and install the new ones. Be sure to check for proper bearing clearances.