Connecting rod bearings gets great loads of stress and are among the causes of catastrophic engine failure. Very tight or stiff bearing problems can result in many problems. Rod bearings can spin, freeze, stretch, deform and endure out-of-round conditions. Connecting rods bearings have precision, surfaces that must handle in a contamination-free environment when inspection and repair is carried out. Human error, lack of proper lubrication and structural failure add to most bearing failures.
- When inner rod bearings have a reduced gap between the bearing surface and the crankshaft, a proper oil film has no space to get to the two surfaces. This increased friction causes heat, making the bearing to expand in the race, thus reducing oil delivery. When temperatures reaches the peak (400 degrees), it leads to annealing or galling of the bearing to the journal race. This often tightens or freezes the bearing against the crankshaft journal. Blue-black marks appear on bearings and journals that have been extremely overheated.
- A very tight bearing can be the cause of an out-of-sequence torque procedure, or a torque pressure that is out of the manufacturer’s specifications. The bearing surface will rob against the journal, creating excessive friction and heat. Over-torqued or over-tightened bearings can cause the rod end cap to bow in the center, leading to an out-of-round profile. The center gap in the bearing will chafe and create vibration with each revolution, degrading the bearing material and removing small metal particles. This causes vibration and rod knock that gets gradually worse.
- Tightened or crushed bearings can spoil the oiler hole alignment between the crankshaft journal and the bearing oiler hole, creating a reduced flow of oil to the bearing surface inside the connecting rod journal., temperatures rise and bearing material becomes scuffed when there is no proper lubrication keeping the bearing from contacting the journal. Repeated scuffing leads to excessive gap and rod knock.
- Tight bearings can cause excessive connecting rod bolt stretch. Bolt stretch results in weakening and tearing of the threads inside the rod cap. Bolts subjected to such stress weaken prematurely and lose their tensile strength and ability and cannot be reused and expected to show proper torque numbers.to check this, bolt stretch gauges should be used to measure the length of bolts when they have been fully loaded and torqued to specifications.
- Tightened bearing will heat up from friction and send off particles of metal that degrade the bearing surfaces. The clearance between the journal surface and bearing surface spoils, opening up with great clearance. This makes the rod to pound in its seat, creating vibration in the rotational axis of the connecting rod. Thus resulting in throwing a rod or a spun bearing results.
- Tight bearings leads to removal difficulty of the connecting rod bolts. This is because bolts can freeze in position, thus requiring the use of air power tools to aid their removal. Bolts that are difficult to move in their threads must be heated or extracted with the use of special tools, such as sharp fluted bolt and nut extractors. Bolt breakage requires Easy-Out tools, including extensive drilling and tapping.