Car con rod bearing

How to detect the connecting rod thin-shell bearings failure

Diagnosis of the connecting rod gear is not only quite time consuming, but also requires special equipment. That is why, it is best to be performed at a service station.

Checking the status of the main crankshaft bearings is carried out in several stages. First, you have to measure the oil pressure in the main line. A special manometer is used for this purpose, equipped with a connecting sleeve and a damper to smooth the lubricant pulsations. You need to connect it to the oil filter housing and measure the oil pressure when the engine is warmed up at idle.

If the pressure is below normal, the next inspection stage is carried out: listening to engine knock with an automotive stethoscope. The inspection is carried out with the engine off, and its performance is simulated by means of a compressor-vacuum pump. Connecting rod thin-shell bearings usually produce a knock of medium volume, but more sonorous than the main bearings.

When knocks are detected the gaps between the mating components are measured using special equipment. If they exceed the permissible rate, the engine is dismantled and the bearings are inspected. Change of their surface color, flaking, corrosion and warping not only indicate that the parts require replacement, but also identify the cause of the failure.

You may identify that the connecting rod thin-shell bearings need diagnosis by the following symptoms:

• knocking of the hot engine, accompanied by  the oil pressure indicator light flashing;
• low oil pressure;
• random engine stops.

Causes of the connecting rod thin-shell bearings failure

Connecting rod thin-shell bearings perform in the conditions of increased loads and are highly exposed to abrasive wear. Their premature abrasion can occur due to a decreased pressure in the engine lubrication system, usage of poor quality or substandard oil or its insufficient viscosity: too thin oil film does not sustain high loads and becomes destroyed. This results in overheating of the crankpin journals and bearings, their melting and warping.

Insufficient oil film strength can also occur due to the ingress of fuel or cooling fluid into the engine lubrication system, because of which the lubricant viscosity is reduced. Compounds with high viscosity are also hazardous for the engine, since at the moment of start, especially in cold seasons, its components are not sufficiently lubricated.

Premature failure of the connecting rod gear components can as well result from the delayed oil or oil filter replacement. Contaminants contained in the lubricant act as abrasive particles, leading to increased scuffing of the mating surfaces.

The useful life of connecting rod bearings is greatly dependent on the driving style. Frequent short distance trips, driving at low rpm, sharp starts and acceleration lead to fatigue deformation of the parts and their corrosion.

Replacement of the connecting rod thin-shell bearings

The replacement of parts is carried out at every major engine repair on a mandatory basis., Oversized bearings of a larger thickness are installed instead of worn out parts, and the crankshaft is bored and polished. Restoration work requires accuracy, so it is possible only at a service station.