Engine Connecting Rod Bearing Failure

Fig 5 edge wear due to distorted connecting rod.

Engine connecting rod bearing failure. Rod knock which is a stabilized hammering increasing linearly with rpm occurs when excess clearances as a result of bearing wear cause the rod big ends to beat against the crankshaft at the bottom and top of the piston stroke. A spun rod bearing may also be caused by wearing down of the bearing with time or even due to improper assembly in the engine. In the latter case a connecting rod or bearings may be loosely installed resulting in excess clearance noise and damage. Rod bearings receive enormous loads of stress and rank high on the list of catastrophic engine failure.

Another common cause of rod failure is a bearing seizure. Pin failure the pin that connects the connecting rod to the piston called the piston pin wrist pin or gudgeon pin gets a lot of wear. Clearances and component geometry retard ignition or use fuel with higher octane number. Other causes of engine bearing failure.

One symptom of engine bearing failure is noise in the engine. The following are typical assembly errors most often made in the installation of engine bearings. Rod bearings can spin freeze stretch deform and suffer out of round conditions. Fatigue cracks may also form in the affected area.

2 4 correct reversed position of offset connecting rod reversed bearing caps in wrong or. Tight or stiff bearing problems can be the result of many factors that lead to their malfunction. In many cases misassembly will result in premature failure of the bearing. Distorted bent or twisted connecting rod is one of the causes of localized loading of engine bearings resulting in excessive wear of the bearing surface along the bearing edge.

Connecting rod end clearance fillets at end of crankpin should not bind on ends of rod bearing 004 10mm to 010 25mm clearance recommended. Possible causes of connecting rod distortion followed by edge wear. Most car drivers have known about rod knock symptoms if not detected it themselves. Excessive idling can result in an oil film that can not support the load needed.

Such a failure may or may not be the rod s fault. Bearing spread main bearings 005 13mm to 020 50mm in excess of crankcase bore diameter connecting rod bearings 020 50mm in excess of rod bore finish of rod bores. If a bearing isn t set into place securely lubrication will be insufficient and cause failure. If the oil film between the rod bearing and crank journal goes away for any reason even for an instant it can overheat and seize the bearing.

Engine bearings will not function properly if they are installed incorrectly. When damage to a rod bearing is confirmed it should be replaced. Either way the engine is going to need a new rod.