Connecting Rod Failure in 4 Stroke Petrol Engines

In summary, the conversation discusses a recent failure of a connecting rod in a 4-stroke petrol engine. The small end of the rod broke into two parts and there are concerns about the root cause of the failure. Possible reasons such as manufacturing flaws, fatigue, and over-revving are mentioned. The conversation also mentions the use of magnaflux inspection for detecting cracks and the possibility of a blocked water passage or improper lubrication leading to the failure. Photographs of the failed surface will be provided for further analysis.
  • #1
mrajm
13
0
hi..
I am new to this site.
I want to know about reasons of failure of connecting rod of 4 stroke petrol engine. In this case the rod has broken into two parts from the small end of the rod. The manufacturing root of the component is hot forging - hardening - induction softening of the small end part - bend/twist correction - machine. What can be the possible causes of the failure?
 
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  • #2
see this thread - Oct26-10, 11:06 PM #1
ChrisCarey

Looking for opinions on connecting rod failure
 
  • #3
Did the piston seize? Small end failure is very unusual unless it's consequential.
 
  • #4
brewnog said:
Did the piston seize? Small end failure is very unusual unless it's consequential.

On the part which remained undamaged in the block there is no mark of rubbing or seizure as such. Your point that it is quite unusual is correct as we have only received 6 cases out of around 5 lack engines we have produced, The big end is well in tact and appears to have no signs of improper lubrication,
 
  • #5
i would say that the small end broke due to fatigue or a flaw. was the rod magnafluxed for cracks? was it inspected for cracks? I think the small end snapped because the piston did not move and the crankshaft did and therefore the con rod broke...now why this happened is known...maybe there was a blocked water passage around this cylinder..maybe the crankshaft was not oiling the bottom of the piston properly, maybe that cylinder had a lean fuel/air mixture. the rod , if in tact , without cracks should never have failed.
 
  • #6
I agree that it was most likely a manufacturing flaw or fatigue, but is it possible that the thing was over-revved so badly that the "rod stretch" became infinite?
 
  • #7
Ranger Mike said:
i would say that the small end broke due to fatigue or a flaw. was the rod magnafluxed for cracks? was it inspected for cracks? I think the small end snapped because the piston did not move and the crankshaft did and therefore the con rod broke...now why this happened is known...maybe there was a blocked water passage around this cylinder..maybe the crankshaft was not oiling the bottom of the piston properly, maybe that cylinder had a lean fuel/air mixture. the rod , if in tact , without cracks should never have failed.

Thanks for the response..
Ok.. All the produced cam shaft go through magnaflux inspection as it is forging root. The possibility remains that the crack was not exposed after machining. There is no visible scoring mark or sign of seizure between the gudgen pin and the small end so for now we can rule out lack of lubrication. I will check the other two points and come back to you...
I will also try to provide photographs of failed surface so that something can be concluded on hardness, crack etc.
 

1. What is a connecting rod and what does it do?

A connecting rod is a vital component in a 4 stroke petrol engine that connects the piston to the crankshaft. It plays a crucial role in converting the linear motion of the piston into rotational motion of the crankshaft, which ultimately powers the vehicle.

2. What causes connecting rod failure in 4 stroke petrol engines?

There are several factors that can contribute to connecting rod failure, including poor lubrication, excessive heat and pressure, manufacturing defects, and over-revving of the engine. In some cases, a failed rod bearing can also lead to connecting rod failure.

3. How can connecting rod failure be prevented?

Regular maintenance and oil changes can help prevent connecting rod failure. It is also important to avoid over-revving the engine and to ensure proper lubrication. Using high-quality parts and avoiding excessive heat and pressure can also help prevent this type of engine failure.

4. What are the signs of connecting rod failure?

Some common signs of connecting rod failure include knocking or rattling noises coming from the engine, loss of power and acceleration, and low oil pressure. It is important to address these issues immediately to prevent further damage to the engine.

5. Can a connecting rod failure be repaired?

In most cases, connecting rod failure cannot be repaired and will require a replacement. It is important to address the issue as soon as possible to prevent further damage to the engine. Regular maintenance and addressing any issues promptly can help prevent connecting rod failure in the first place.

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