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All You Need to Know About Transmission Parts
5 Symptoms of a Bad Brake Rotor

5 Symptoms of a Bent Connecting Rod 

What is a connecting rod

  • A connecting rod is the connection between the piston and the crankshaft in an internal combustion engine. When the crankshaft rotates, the piston makes a rapid reciprocating motion, exposing the connecting rod to a large, manageable force.
  • It is one of the main parts of the engine power transmission, the shape of the rod body is “I” type, requiring high density and low mass.
  • The main function of the piston connecting rod set is to be subjected to the pressure of the combustion gas, and this force is transmitted to it through the piston pin and then to the crankshaft, and the reciprocating motion of the piston is transformed into the rotational motion of the crankshaft.
  • The connecting rod consists of three parts: the big end, it and the small end. The big end is connected to the crank pin using a bearing; the small end is connected to the piston pin (this pin is called a wrist pin, a cylindrical pin or a gut pin)
  • A variety of materials are used for connecting rods, including carbon steel, iron-based sintered metal, micro-alloy steel, and spheroidal graphite cast iron.


The main symptoms of connecting rod bending

  • Only when the connecting rod has a certain strength, the engine can work. A bent connecting rod prevents the engine from forming a combustible mixture and makes starting difficult.
  • This is a bad situation that every driver does not want to see. This is because the engine will start with an unstable idle speed and a strange noise, and there will be no more intake stroke, exhaust stroke, compression stroke or power stroke.
  • The driver can quickly notice when this happens because there are several more obvious symptoms. The following are common symptoms that reflect it failure.
(1)Low Compression
  • Imagine that it is slightly bent and you continue to use it without much problem. However, continued bending will result in limited compression of the cylinder.
  • If you suspect the possibility of a bent connecting rod, it is recommended that you perform a compression test. If your compression coefficients differ from each other by more than 10% on all cylinders, then you may have a rod problem.
  • Note that in addition to bent rods, leaks can also cause low compression. If the compression test is not satisfactory, consider performing a leak down test to further diagnose the cause.


(2)Engine Popping Sounds
  • Deformed connecting rods and pistons will basically deflect and cause a noise when the engine starts. A bent connecting rod will deflect the direction of the cylinder reciprocating motion, causing the piston motion to make a knocking sound when changing direction.
  • This will be a moderate and short knocking sound, proportional to the engine speed. However, when the temperature changes, the sound remains the same.
  • When the engine is circulated and lubricated by the oil, the sound disappears for a short time, indicating a possible rod failure.
(3) Low oil pressure
  • If your connecting rod is damaged or malfunctioning, a large amount of oil in your engine will go missing, which will have a catastrophic effect on the oil pressure of your engine.
  • If you check the oil pressure gauge on your engine, you will see that the oil pressure is reduced. The instrument panel will also illuminate a warning light in due course
  • Without sufficient oil to lubricate the engine, wear will be severe and it is never a wise choice to continue driving at this point, as this will cause the engine to overheat and cause you even greater financial loss.
(4)Rods are significantly bent or damaged
  • The connecting rod set is subject to alternating loads such as compression, tension and bending during operation, so it body may be bent and twisted out of shape. Deformation of the connecting rod that affects normal function is relatively easy to observe, provided you have disassembled the engine.
  • Considering the serious consequences of this, you will have to disconnect it to inspect the connecting rod. Fortunately, other aspects of the engine can also be checked at this time, and the connecting rod is relatively easy to replace.


(5) Impounded engine
  • People often see thrown rods causing the entire engine to seize or even stall. This is very good to determine, as long as you can not turn it over you by hand (using the wrench on the crankshaft pulley bolt), then the engine is stuck.
  • A thrown rod will also produce a noticeable crashing sound accompanied by metal flying out of the engine compartment. You may notice a large hole under the engine with a puddle of oil leaking from the corresponding location.
  • The purpose of engine connecting rod replacement is to extend the life of the engine and reduce the noise generated by engine operation.
  • Although some connecting rods are bent to such a low degree that the naked eye cannot distinguish them, they can cause eccentricity of the piston when used, and after long hours of work, there will be severe wear on the piston and piston ring side, resulting in early engine overhaul.
  • If the slight deformation of the connecting rod is not replaced in a timely manner, over time, the serious deformation of the connecting rod will occur crankshaft seizure, fracture, serious damage to the block, crankshaft and other failures
  • In addition, in the case of engine water, due to the incompressibility of water, the piston movement will become shorter, resulting in engine rod bending or fracture, extreme conditions will cause the fracture rod flying out through the cylinder block.
  • The degree of bending of the connecting rod is different, you can use a micrometer to measure, if within the limits can be used, if there is no professional measuring equipment, all the replacement is the safest.
  • If two connecting rods are broken because of water ingress, then the remaining two need to be replaced together, 4 connecting rods and 4 pistons are replaced at the same time, which is a normal maintenance operation. Replace the engine connecting rod alone is not conducive to stability later.
  • The connecting rods are relatively easy to replace, but the engine needs to be opened by professionals. In view of all the symptoms, I believe that every driver does not want to encounter such a headache, we recommend that you replace them in time to prevent the problem.

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