Pontiac Fiero 1984-1988 Repair Guide

Main Bearings

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CHECKING BEARING CLEARANCE



  1. Remove the bearing cap and wipe the oil from the crankshaft journal and the outer and inner surfaces of the bearing shell.
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  3. Place a piece of plastic gauging material in the center of the bearing.
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  5. Use a floor jack or other means to hold the crankshaft against the upper bearing shell. This is necessary to obtain accurate clearance readings when using plastic gauging material.
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  7. Install the bearing cap and bearing. Place engine oil on the cap bolts and install. Torque the bolts to specification.
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  9. Remove the bearing cap and determine the bearing clearance by comparing the width of the flattened Plastigage® material at its widest point with the graduations on the Plastigage® 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 the clearance after replacing the shells. (Refer to Main Bearing Replacement).
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REPLACEMENT



Main bearing clearances must be corrected by the use of selective upper and lower shells. Under no circumstances should the use of shims behind the shells to compensate for wear be attempted. To install the main bearing shells, proceed as follows:

  1. Remove the oil pan as outlined below. On some models, the oil pump may also have to be removed.
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  3. Loosen all main bearing caps.
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  5. Remove the bearing caps and remove the lower shell.
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  7. Insert a flattened cotter pin or roll pin in the oil passage hole in the crankshaft, then rotate the crankshaft in the direction opposite to cranking rotation. The pin will contact the upper shell and roll it out.
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  9. 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 reconditioned or replaced.
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The journals can be measured for out-of-round with the crankshaft installed by using a crankshaft caliper and inside micrometer or a main bearing micrometer. The upper bearing shell must be removed when measuring the crankshaft journals. Maximum out-of-round of the crankshaft journals must not exceed 0.037mm (0.0015 inch).

  1. Clean the crankshaft journals and bearing caps thoroughly for installing new main bearings.
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  3. Apply Assembly Lube, No. 1050169 or equivalent, to the thrust flanges of bearing shells.
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  5. Place a new upper shell on the crankshaft journal with locating tang in the correct position and rotate the shaft to turn it into place using a cotter pin or roll pin as during removal.
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  7. Place a new bearing shell in the bearing cap.
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  9. Install a new oil seal in the rear main bearing cap and block.
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  11. Lubricate the main bearings with engine oil. Lubricate the thrust surface with Assembly Lube 1050169 or equivalent.
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  13. Lubricate the main bearing cap bolts with engine oil.
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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 wood or rubber mallet before the attaching bolts are installed. Do not use attaching bolts to pull the main bearing caps into their seats. Failure to observe this information may damage the cylinder block or a bearing cap.

  1. Torque the main bearing cap bolts to the specification in the Torque Specifications chart in the beginning of this section.
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