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I've got a potential one of three. I cannot determine if the knocking/clunking noise is necessarily a rod noise. And I won't be able to determine if the bearings are bad until i pull the motor. (Not going to happen anytime soon). When we did the compression at a ttnet owners home, I believe he made it clear that the sound was only on the passangers side bank. this can be confirmed because we could hear addition noise through the passangers exhaust only. again, compression was dead on and done with precision. that's a helpful post... thanks!
: Making The Diagnosis
: Symptoms that may indicate bad bearings include: : • Low oil pressure - due to excessive clearances between the bearings and crankshaft, either because of wear or bearing damage. But low oil pressure may also be caused by a worn oil pump, restricted oil pump pickup screen, faulty oil pressure sending unit, low oil level in the crankcase or low oil viscosity. : • Rod noise - rapping noises that increase with rpm are a telltale symptom of excessive clearances in the rod bearings. The underlying cause may be bearing wear, bearing damage, a loose or cracked rod cap or low oil pressure. : • Engine seizure (spun bearing) - the final stage of bearing failure that may occur when metal meets metal with little or no lubrication in between. Causes here include oil starvation (check oil level and engine for oil leaks), oil breakdown (lack of maintenance), oil contamination (internal coolant leaks or dirt), failed oil pump, oil pressure relief valve stuck open, etc. : There are two important points here. One is that if you suspect bad bearings, the only way to know for sure is to pull the oil pan, remove some main and rod bearing caps and inspect the bearings. If the bearings are worn, they need to be replaced. But if they show evidence of damage or unusual wear, it’s pointless to replace them until you’ve diagnosed the underlying problem. : At this point in the process, you have to make the call as to whether replacing the bearings is worth it or not. If the bearings are only worn and everything else appears to be okay, a new set makes sense. On the other hand, if the bearings are damaged or smeared, the crankshaft may need to be reground or replaced, and one or more connecting rods may have to be reconditioned, straightened or replaced. It all depends on the damage and what further inspection reveals. : Reading The Bearings
: As the rod and main bearings are removed, they should be cleaned and placed in order for a close visual inspection. The condition of the bearing surfaces should be noted along with any unusual wear patterns that appear on adjacent bearings. : If a rod bearing failed and was the one furthest from the oil pump, the engine may have an oil supply problem. If a single rod bearing that failed was not the one furthest from the crank, and the other bearings are okay, there may be an obstruction in the crankshaft oil passages that feeds the bearing. : Other reasons for an individual rod bearing failure include a rod bore that’s out-of-round or stretched, rod bolts that have stretched, rod nuts that have come loose or were not properly torqued, a twisted or bent rod, an out-of-round or rough crank journal, and detonation or preignition in the related cylinder. : All bearings will show some degree of wear. If you see scoring or wiping, dirt or other debris embedded in the surface of the bearings, or pitting or flaking, it indicates other problems that may also need to be identified and corrected. : If dirt or other abrasives get into an engine’s crankcase because of poor filter maintenance, the particles can become embedded in the bearings. The softer the bearing material, the greater the embedability - which actually helps prevent damage to the crank journal. But if dirt particles are large enough, they can score the surface of the crank journal requiring the crank to be removed so the journals can be reground and polished. : Most bearings will also show some fatigue damage (flaking) if they accumulate enough miles. Fatigue requires repeated loading over an extended period of time. All metals eventually fatigue if subjected to enough cycles. It’s like bending a paper clip back and forth until it breaks. With engine bearings, the pounding comes from the downward force of every combustion stroke and the upward momentum of the rods and pistons when they reverse direction at the top of every exhaust stroke. Running at high rpm is actually harder on the bearings than high combustion pressures. : If the upper rod bearings in a low mileage engine show fatigue damage, it may indicate engine overloading or detonation. Common causes of detonation damage include an inoperative EGR system, overadvanced ignition timing, a lean fuel mixture, poor engine cooling or a dead knock sensor. : Bearings that are blued or discolored would tell you they’ve seen too much heat. Bearings are cooled primarily by oil flow between the bearing and journal. Anything that disrupts or reduces the flow of oil not only raises bearing temperatures but also increases the risk of scoring or wiping the bearing. Conditions that can reduce oil flow and cause the bearings to run hot include a worn oil pump, restricted oil pickup screen, internal oil leaks, a low oil level in the crankcase, aerated oil (oil level too high) or tight assembly clearances. : Most motor oils start to break down when temperatures exceed 300° F. The ideal oil sump temperature for most engines is 220°-230° F, which may require the installation of an oil cooler or a higher capacity oil pan if a vehicle is used for towing, racing or other hard use. Switching to a synthetic oil that can better withstand high temperatures can also reduce the risk of oxidation and viscosity breakdown under load. : If bearings have a wiped or smeared appearance, the bearing has made contact with the crankshaft journal due to lack of oil, viscosity breakdown, oil dilution or contamination, or insufficient bearing clearance (misassembly). : A good set of bearings can be wiped out if antifreeze finds its way into the crankcase. Coolant is a lousy bearing lubricant, and it doesn’t take much contamination to cause problems. If the oil shows signs of coolant contamination, pressure test the cooling system for internal leaks. A leaky head gasket, cracked block or head may be allowing coolant to mix with the oil. : If the center main bearings show more wear than the end bearings, the crankshaft may be bent or the main bores in the block may be out of alignment. Likewise, if a rod bearing shows uneven wear across the face, the connecting rod may be bent or twisted. : [ http://www.babcox.com/editorial/us/us90126.htm ]
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