GM 12623074 Engine Crankshaft

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The crankshaft can only be removed after the engine has been pulled out of the car on the condition that such parts as the flywheel crankshaft pulley, timing chain cover, oil pan, oil pump body, oil filter, and piston/connecting rod assemblies have been stripped off. Before withdrawal make sure of the crankshaft end float by putting the dial gauge parallel to the crankshaft. Push the crankshaft to the right and then to the rear to bring the indicator to zero then push the crankshaft to the left then note down the reading which should be within the range of 0.003-0.010 inch (0.076 -0.254mm). Sometimes get of clearance can be approximated if dial-indicator is not available by use of feeler gauges. Unbolt the main bearing bridge and then free up and remove the main bearing cap bolts to the point where you can do so without dropping the bearing inserts. It is recommended that you lift the crankshaft out and seeing as they are quite heavy you might have a friend help you. For installation, make sure that the engine block and the crankshaft are clean and likewise check for any signs of damages. Raise the engine block in an inverted fashion, provide no support for the crank and remove any residual support and clean up the bearing surfaces. New upper and lower main bearing inserts have to be fitted, beforehand making sure that the oil holes are in place and aligned; no lubricant shall be applied at this time. Using Plastigage to check the oil clearance and make certain that the Plastigage is installed correctly and the bolts are tighten correctly and compare the width of the crushed Plastigage as shown on the scale. If clearance is not as specified, check the fact that no debris was in evidence when the clearance was measured, and consider machining or replacing the bearing inserts in this case. If you found some Plastigage on the crankshaft, then remove it, and apply some grease or assembly lube to the bearing surfaces and lay the crankshaft back in its position. The main bearing caps should be fitted correctly and oil put on the bolts before tightening as provided for. Lastly, once more adjust the crankshaft end-float and double check it for any drag on it before fitting a new rear main oil seal.

To begin the process of removing the crankshaft, you measure endplay using a dial indicator or feeler gauges. Then remove the main bearing caps and finally the crankshaft itself. The engine block and crankshaft must be cleaned and inspected before installation. After removal of old main bearing caps and inserts, new ones are put in their place. Plastigage is used to check the main bearing oil clearance, and in some cases different bearing inserts may be necessary. When clearance is correct, Plastigage is removed and the crankshaft lifted out of the block of cylinders. The surfaces on which bearings are placed are oiled again for lubrication as it should be done before putting back the shaft into position. After that, tighten up your main bearing caps in sequence while checking your endplay one more time. And finally install rear main oil seal.

The crankshaft as we have earlier seen can only be removed if the engine has been pulled out of the car which means DISASSEMBLED or REMOVED of the driveplate, crankshaft pulley, timing chain, oil pan, oil pump body, oil filter, piston/connecting rod assemblies. The rear main oil seal retainer must be removed by the dismantling of its bolts and then the crankshaft cannot be removed without the removal of this retainer. First tape a dial indicator on the crankshaft and use it to measure the endplay. Loosen the nut on the front of the crankshaft and turn it to bring the dial indicator to zero, then push again; the standard figure should fall in the region of between 0.003 to 0.010 inch. In case the dial indicator is missing, or unavailable, the clearance might be checked with feeler gauges. For a V6, turn the main bearing cap bolts up to but not beyond the point so that they can be undone by hand; for a four-cylinder engine, slacken the lower crankcase bolts in the sequence by which they were tightened. Take off the main bearing caps or lower crankcase as gently as possible so as not to lose the bearing inserts. Remove the crankshaft as it should be done with a help of an assistant and fit back the main bearing cap or lower crankcase half onto the engine block tightening the fasteners only lightly but making sure that the caps are placed in the correct manner. While installing considerfulness of the engine block and the crankshaft and even their wash. Set the we engine block on its bottom, if any initial bearing inserts are there have to be removed and then clean all bearing areas. Place a new upper main bearing insert into each of the main bearing saddles, the oil holes of which must correspond to those of the other component; put in the main lower bearing inserts to the related caps. Clean the faces of crankshaft and bearing insert, then position the crankshaft in the bear. The Plastigage is used to check the oil clearance of the main bearing, while the caps should be properly fitted without interfering with the content observed. Once the bolts have been tightened, the caps are next to be removed, so that the width of the Plastigage can be compared to the scale in order to check the clearance. If clearance is wrong check cleanliness and if necessary consider other bearing inserts. All traces of Plastigage should be cleaned off carefully. Before the bearings are finally installed, the faces of the bearing inserts should be wiped clean with a clean rag; a thin layer of grease or assembly lube should then be applied; this is when the crankshaft should be placed back in its usual position. Dry and clean the bearing insert faces and lubricate lightly while making sure there is no oil between the two then mating surfaces. All the bolts are to be installed and tightened and if they are lost, they have to be procured and used The crankshaft end play has to be checked again. This has to be done in order to check for binding of the crankshaft thus if it turns freely. Last, there is the rear main oil seal that should be put in its new one.

During installation, the engine block and crankshaft must be cleaned and inspected.

During installation, ensure the engine block and crankshaft are clean. Check the main bearing oil clearance using Plastigage, comparing the crushed width to the scale provided. If clearance is not as specified, verify cleanliness and consider replacing bearing inserts if necessary.

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