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Yamaha F250 broke connecting rode

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ashraf

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I have a 2015 Yamaha F250 4 stroke with only 30 hours. All of the sudden the connecting rod broke in half and breaking the cylinder block. I am in the process of changing the block and the connecting rod and piston. My concern is what could be the reason for such thing so it would not happen again. The engine was running fine when at the time of this problem. I am attaching a picture of the piston with the connecting rod and the block, the strange this is the it seems that the rod was bend before breaking.
 

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racerone said:
Warranty ?----Why do you say it appeared to be bent before breaking ?
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IMO it looks like it had a bend in the rod.

mrxw89.jpg
 
ashraf said:
I have a 2015 Yamaha F250 4 stroke with only 30 hours. All of the sudden the connecting rod broke in half and breaking the cylinder block. I am in the process of changing the block and the connecting rod and piston. My concern is what could be the reason for such thing so it would not happen again. The engine was running fine when at the time of this problem. I am attaching a picture of the piston with the connecting rod and the block, the strange this is the it seems that the rod was bend before breaking.
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Pre-ignition or detonation comes to my mind. Piston is on its way up on the compression stroke. The air/gasoline mix either ignites prematurely on its own (pre-ignition) or after the spark plug ignites the air/gasoline mix the mix explodes (detonates) instead of burning smoothly over time.

The forces in the combustion chamber are so high and violent that they try and push the piston back down in the cylinder at the very time that the crank shaft is trying to move it upwards. Something has to give. Appears to be the rod took the hit. The rod bends, breaks, and then damages the block.
 
Motor is somewhat about four years old. Maximum warranty here in the USA is only three years. Maybe less outside the USA.

In any event, pre-ignition or detonation damage is not covered by the warranty. Warranty is for defective parts. Something external causing the failure of the motor is not covered by the warranty.

A four year old motor with just 30 hours on it tells me it is not being used. Maybe it had very old and degraded gasoline in it. That can result in detonation.
 
This is all correct, Boscoe, but I have some additional thoughts. It would have been making some noises while pre-igniting (especially considering bad fuel), and likely Ashraf would have "backed down". Ashraf, did it just "BAM" with no other warning? You have to consider something could have suddenly happened with the spark timing. When a sudden and catastrophic failure occurs such as this, you have to correct the cause. Defective connecting rods are really quite "out of the question". Had this motor endured a hard "rock strike"? Note: This might be a candidate for a cylinder sleeve, it will save you huge pounds, brother!
 
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In most cases I would agree that something untoward may be heard from the motor before damage ensues. Pinging or rattling normally. Giving an operator time to retard the throttle. Or the ECU on the motor to make an adjustment. But in some few instances the motor is running just fine and then detonation happens. Most times the knock sensor will hear it and take action to self preserve the motor. But then along comes a one in a million instance where detonation happens and kabluey, a rod comes out the side of the block. It can take just one time. Not likely, but it can happen.

The ECU of the F250 may have recorded a knock sensor code having been set.
 
If it is true 30 hrs of operating time then a factory representative may do something for the customer.-----Not sure what Yamaha " Africa " would do for this party.-----What boat is the motor on and what is it used for ??------I am quite sure that other brands of motors would help in this case !!
 
It was not pre-ignition. The piston would fail way before a con-rod with pre-ignition. With Pre-ignition you need a source to light of the fuel..Hot spot, hot plug tip, piece of carbon....
You will see pre-ignition in two stroke engines using crappy 2Stk oil.

BTW, You cannot hear pre-ignition, there is no warning.

Detonation will not fail a con-rod either. It would bust up your ring lands. You would hear detonation.

Looking at your piston pics, neither detonation or pre-ignition caused this.

My best guess is you have hydraulic damage to the con-rod, you took water into the cylinder and bent a rod and it eventually failed.
 
Great, excellent reasoning, Chris. Wonder who dismantled it? Looking for that. Valve bent now too, could be additional head damage, valve seat. How could such a low hours motor get water in it? With bent connecting rod, you would notice a miss....very low compression on affected cylinder. Asking Ashraf if it fired up with a " jolt " after sitting awhile, perhaps allowing water to accumulate in affected cylinder. Maybe he bought it with bent rod already? Previous owner did the water damage.
 
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racerone said:
Warranty ?----Why do you say it appeared to be bent before breaking ?
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You can see the bend in the rod in both parts of the rod. You can see the difference between the broken and the new one
 

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This is not my engine, it belongs to the Cost guard and they asked me to help figure out the reason of this, they use it in salt water and according to them the valve was not damaged, in any case if the timing was wrong the valve would bend not the connecting rod, right. If detonation or pre-ignition were the reason, how to prevent such a thing in the future?
 
No the valve is not bent and no damage to the cylinder head or the connecting rod bearing. As for the engine it self, it was a brand new engine and they run at least once a week.
 
ashraf said:
This is not my engine, it belongs to the Cost guard and they asked me to help figure out the reason of this, they use it in salt water and according to them the valve was not damaged, in any case if the timing was wrong the valve would bend not the connecting rod, right. If detonation or pre-ignition were the reason, how to prevent such a thing in the future?
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Did you read post #10? Forget about Pre-ignition and detonation.

The boat belongs to the CG. I would say they Did a full throttle Fwd into reverse for an emergency stop. That will fill the cylinders with water. Ask me how I know this.

What you have to understand....they will never tell you what really happened.
 
timguy said:
Great, excellent reasoning, Chris. Wonder who dismantled it? Looking for that. Valve bent now too, could be additional head damage, valve seat. How could such a low hours motor get water in it? With bent connecting rod, you would notice a miss....very low compression on affected cylinder. Asking Ashraf if it fired up with a " jolt " after sitting awhile, perhaps allowing water to accumulate in affected cylinder. Maybe he bought it with bent rod already? Previous owner did the water damage.
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You would never feel the difference.
 
Right, the crankshaft end would seize, causing this, BUT THE BEARING IS FINE! I have seen how the Coast Guard can "test" equipment. It either hydrolocked, or was over revved. No one in their right mind would throw it into reverse while going full throttle, even the Coast Guard. They are trained on proper operation proceedures. This piston let loose on the upstroke, whichever valve then opened when the piston was topsided to the head, is likely bent. If the rod was "S" shaped and running before the final break, there would have been a noticeable miss. With that piston falling even 8mm shy, it would have produced less than 20% of normal compression. Go ahead, take 8mm off the stroke and do the math. Start with normal ratio 10.3:1. A V6 running on 5 cylinders? Who wouldn't detect a miss?

Note to Chris! I'm here to help the customer, and I'm not enjoying constantly being put in a position to defend my answers and suggestions. I'm basically supporting you on your thinking here! See post #11.
 
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