GM 12480255 Bearing Kit,Connect Rod

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Remove the oil pan, oil pump, and cylinder heads as previously described. Before forcing the piston assemblies up through the top of the engine block, use a ridge reamer to eliminate the ridge or carbon deposits at the top of each cylinder, working on one cylinder at a time. Turn the engine so the piston is at the bottom of its stroke, place a rag on top of the piston to catch cuttings, and after removing the ridge, crank the engine to the top of the cylinder to remove the cloth and cuttings, as failure to do so may damage the piston rings, pistons, or cylinder walls. Inspect the connecting rods and caps for cylinder identification, marking them with a small punch if necessary. Remove the nuts on the connecting rod stud in sequence and lift the cap off the crankshaft, placing the cap and bearing on a clean work surface marked with the corresponding cylinder number. Cover the connecting rod studs with rubber or plastic tubing to prevent damage to the crankshaft or cylinder wall during the removal of the piston assembly. Push the piston/connecting rod assembly out through the top of the cylinder and place it next to its rod cap in the sequenced work area, repeating the process for the remaining cylinders while reusing the tubing. Remove the bearings from the connecting rods and caps using a small screwdriver, and if the engine has high mileage, consider replacing the bearings rather than reusing them, placing any to be reinstalled in a numbered rack. If available, use a piston ring expanding tool to remove the rings from the piston, or alternatively, expand the ring just enough to clear the lands and use strips of tin to walk the ring off the top. Place the rings in their installed order next to the piston/connecting rod on the numbered work area. To separate the connecting rod from the piston, remove the piston pin, a task best left to a dealer or automotive machine shop with the proper tools. Avoid cleaning and inspecting the piston/rod assemblies at this stage, as they may need to be replaced depending on the condition of the cylinder block or crankshaft.

To overhaul an engine, it is important to replace both main and connecting rod bearings with new ones; nevertheless, for a closer examination of the engine condition, old bearings must be kept. Failure of the bearing may arise from many different reasons such as lack of lubrication, presence of dirt and or foreign materials, overloading the engine or even corrosion that would require immediate correction to avoid its reoccurrence during engine assembly. In order to study these bearings, they are removed carefully from several locations such as the engine block, main bearing caps, connecting rods and rod caps after which they can be put on a clean surface so that any problem can be identified easily by matching them with corresponding crankshaft journal. Foreign particles which may enter the engine through various routes pose a threat to bearing integrity (McCallion 2013). This calls for thorough cleaning of engine parts and cleanliness maintained during assembly to prevent such occurrences. Also, regular oil and filter changes are recommended. Lack of proper lubrication due to factors like high temperatures, overloading, oil leakage or blocked oil passages can cause damage to the bearing material that is usually depicted by extrusion from steel backing or even steel backing discoloration caused by overheating. Similarly driving habits such as full-throttle low-speed operation and short trips may negatively influence the life span of bearings due to insufficient heat in the engine and consequent accumulation of corrosive substances in the oil. Lastly incorrect bearing installation at time of assembling an engine like having too tight bearing fits or allowing dirt or foreign material into the system can result in inadequate oil clearance as well as high spots on the bearing leading to final failure of the bearing itself.

When working with Plastigage, three precautions are essential, first, before carrying out the test, it is advisable for all the surface of the crankshaft and bearing surfaces that are in contact with the Plastigage to be free from any traces of oil and grease as the compound is soluble in oil; secondly, ensure that once the Plastigage has been fitted in the crankshaft or any other engine part that it does not get into contact with the crankshaft or the engine any other way Whenever an engine is undergoing overhaul, it is necessary to always check the bearing clearances and this applies to the used and the new bearings. The working of the procedure for the main and connecting rod bearings is analogous. First of all, fit the main bearings and caps into the engine block, make sure crankshaft and bearing surfaces thoroughly washed with oil, dirt, any other unwanted substance. Put a strip of Plastigage at the main bearing journal of the crankshaft and then fit each main bearing cap and fasten its bolts to the required tightness with the arrow on each cap pointing frontwards. Read and retain the bearing number stamped on the bearing, then , after tightening, dismantle each bearing cap and measure the width of the compressed Plastigage strip with reference to the scale exhibited on Plastigage envelope to understand the state of clearances for each bearing. As with most rotational equipment, if the Plastigage is much more flattened at the two ends than in the middle or, conversely, if the flattening is most pronounced in the middle, this is indicative of journal taper. It can be detected when all the Plastigage is removed, when the crankshaft has turned 90 degrees; then, check again the clearances with the Plastigage; by comparing the measurements made above with these latter, the eccentricity can be assessed. For connecting rod bearing clearances, it is necessary to install each piston/rod assembly and use such measure as Plastigage mentioned above. Also, it is possible to measure connecting rod side clearance at this time, if necessary. Any that are out of tolerance should be removed and replaced with bearings of the correct size; upper and lower bearings must ALWAYS be replaced in pairs.

Remove the oil pan, oil pump, and cylinder heads as previously described. Before forcing the piston assemblies up through the top of the engine block, use a ridge reamer to eliminate the ridge or carbon deposits at the top of each cylinder. Work on one cylinder at a time by turning the engine so the piston is at the bottom of its stroke, placing a rag on top of the piston to catch the cuttings. After removing the ridge, crank the engine until the piston is at the top of the cylinder and then remove the cloth and cuttings, as failure to do so may damage the piston rings, pistons, or cylinder walls. Inspect the connecting rods and connecting rod caps for cylinder identification; if not plainly marked, use a small punch to make indentations (left bank - 1, 3, 5, 7, right bank - 2, 4, 6, 8). Remove the nuts on the connecting rod stud in sequence and lift the cap (with bearing inside) off the crankshaft, placing the connecting rod cap and bearing on a clean work surface marked for each cylinder. Cover the connecting rod studs with rubber or plastic tubing to prevent damage to the crankshaft or cylinder wall during piston assembly removal. Push the piston/connecting rod assembly out through the top of the cylinder and place it next to its rod cap on the sequenced work area. Repeat these procedures for the remaining seven cylinders, turning the crankshaft as necessary to access the connecting rod nuts, and reuse the rubber or plastic tubing for each assembly. Remove the bearings from the connecting rods and connecting rod caps using a small screwdriver; if the engine has many miles, it is not advisable to reuse the bearings, but if they are to be reinstalled, place them in a numbered rack. If a piston ring expanding tool is available, use it to remove each of the rings from the piston; alternatively, expand the ring just enough to clear the lands of the piston body, then place strips of tin (about ¾ in. wide) under the ring at equal distances around the piston and use a slight twisting motion to 'walk' the ring up and off the top. Place the rings in their 'installed' order adjacent to the piston/connecting rod on the numbered work area. Separating the connecting rod from the piston requires the removal of the piston pin, a task best left to a dealer or automotive machine shop equipped with the proper support tools and an arbor press. Avoid cleaning and inspecting the piston/rod assemblies at this time, as they may need to be replaced with new units depending on the condition of the cylinder block or crankshaft.

When an engine is overhauled, old main and connecting rod bearings have to be replaced with new ones, but the old bearings are useful for analyzing the working condition of the engine. Some of these are lack of adequate lubrication, the presence of dirt or any foreign particle, overloading the engine, corrosion and many others, all these must be tackled before the engine is reassembled to avoid a repeat of the same mishap as far as bearing failure is concerned. When inspecting the bearings they should be taken of the engine parts and arranged neatly in their respective positions on a flat surface so as to pair any defect with the respective crank shaft journal. Foreign particles can be either preformed, that is, deliberately introduced at assembly, through filters or the PCV system or postformed after the machining or reconditioning of the engine. Small contaminants can be taken into the bearing surface and cause localised damage, whilst larger particles can cause scoring or gouging. To avoid such failures, cleaning all the parts is essental as well as frequent oil and filter changes. Some cause of inadequate lubrication include heat, overloading, leaks, and blocked oil flow passages which might dangerous where most of the bearing material is removed to exposed the metal where temperatures are also high. Some driving practices therefore also affect bearing life; asmentioned by Reynolds RPMs at low speeds in full throttle applying high loads that expel oil and short trip that cause corrosion due to low heat buildup. Secondly, bearings are very sensitive to, for example, improper internal bearing interference that leads to oil starvation or the generation of high spots that lead to failure.

In the process of overhauling an engine, though new main & connecting rod bearings are used, incorporating the worn ones for inspection can be highly informative of the heath of the engine. Major causes of bearing failure include impact, corrosion, severe loading or overloading of the engine, and foreign particles such as lack of lubrication and dirt and any of these must be rectified before the bearing is reinstalled to avoid a repeat. To examine the bearings unbolt them off from the engine block and arrange them in conjunction with the main bearing caps together with the connecting rods and rod caps on a clean surface which will enable one to match any defects on the bearings with the corresponding crankshaft journal. Particles may be picked up during the assembly process, through filters or breathers, or result from metal chips and abrasives which are left in components which have been reconditioned. The carrying particles, which are of a smaller size, may become lodged into the softer bearing material: larger particles may scratch or cut into the bearing and the shaft. Prevention can be achieved by regular cleaning of all the components and constant oil and filter replacement. Failure of lubrication may be due to high operating temperature, overloading, leakage of oil and blocked oil ways that may cause rubbing off bearing material from the backing or extrusion of the backing at very high temperature. Driving behavior also influences the bearing life; high cyclic operating speeds and low speeds result in high load and can eliminate the oil film, short trips can result in corrosion due to low heat. There are other forms of failures for example, tight bearing fit or dirt trapped behind the inserts.

With the pistons complete with piston rings and connecting rods, they can be installed in the engine. Ensure the cylinder bores are perfectly clean by wiping the cylinder walls several times with a light engine oil and a clean, lint-free cloth. Lubricate the connecting rod bearings and install them into their appropriate rod and rod cap. Lightly coat the pistons, rings, and cylinder walls with light engine oil. To prevent the threaded bolts from possibly damaging the cylinder wall or crankshaft journal during installation, place a length of rubber or plastic tubing over the connecting rod studs on one rod assembly, using a piston ring compressor and pieces of rubber hose. Check that all the piston ring gaps are positioned properly. Verify that the piston/rod assembly is correctly positioned, noting that most pistons will be marked with an 'F' or a drilled-out area indicating the front of the engine, while the rod bearing tang slots should face the outside of the engine block. Place a piston ring compressor around the piston, ensuring the base is flush with the cylinder block, and tighten it until the rings are flush with the piston surface before pushing the piston assembly into the bore. A wooden hammer handle can be used to tap the top of the piston slightly, holding the ring compressor firmly against the cylinder block until all rings are inside the bore, then continue pushing until the connecting rod is near its installed position. Ensure all bearing surfaces and the crankshaft journal are coated with engine oil, then remove the tubing protector pieces and install the connecting rod bearing cap with bearing to the connecting rod, fitting it over the crankshaft and connecting rod studs. Torque the nuts to specifications and repeat the procedure for all cylinders, using the rubber or plastic tubing on each assembly to prevent damage as the pistons are pushed into place, rotating the crankshaft as necessary to make the connecting rod nuts accessible for tightening.

Three precautions are essential: 1. Ensure that all oil and grease are removed from the crankshaft and bearing surfaces during testing, as Plastigage is soluble in oil. 2. Do not rotate the crankshaft while Plastigage is installed to avoid damaging the crankshaft or engine surfaces. 3. Carefully remove all traces of Plastigage after testing, using a fingernail or a blunt wood stick to prevent harm to the crankshaft or bearing surfaces.

The cylinder bores should be perfectly clean, which can be achieved by wiping the cylinder walls several times with a light engine oil and a clean, lint-free cloth.

Driving habits significantly impact bearing longevity; for instance, full-throttle low-speed operation can create high loads that squeeze out oil, while short trips can lead to corrosion due to insufficient heat.

Bearing clearances should be checked whenever an engine is overhauled, applicable to both reused and new bearings.

The piston assembly should be pushed into the bore after tightening the ring compressor until the rings are flush with the piston surface. A wooden hammer handle can be used to tap the top of the piston slightly while holding the ring compressor against the cylinder block until all rings are inside the bore.

Remove the bearings from the connecting rods and caps using a small screwdriver.

It is important to check that all the piston ring gaps are positioned properly.

If the bearings are not within tolerances, they should be replaced with correctly sized bearings, ensuring upper and lower bearings are replaced as a unit.

Remove the bearings from the connecting rods and caps using a small screwdriver.