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Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 10011
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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breaking rod in half on random cylinders on 2005 225 merc

Resolved Question:

breaking rod in half on random cylinders on 2005 225 merc outboard altama engine any sugestions
Submitted: 11 months ago.
Category: Boat
Expert:  Jason replied 11 months ago.

Hello, my name is XXXXX XXXXX I will be helping you today.

I read what you wrote, and i'm sorry to hear your having all this troubles. But I don't understand what you are asking, what do you mean by "any suggestions"? Are you asking why the rods are breaking? Is a mechanic already working with you on this issue? Were these all brand new from the factory engines, or where they ever rebuilt or opened up by somebody?

Customer: replied 11 months ago.

any reason why rod are breaking in half pistons are not gauled rods just breaking after new power heads installed went back to dealer to make sure all timings oil injectors were proper this power head has run since febuary of this year ,broke a rod 2 weeks ago new power heads all time we have changed them

Expert:  Jason replied 11 months ago.

Conencting rods only break for a couple of reasons. And I have a few more questions for you here. Please answer them in the order I ask them. If you can label your responses with numbers that will make for easy reading.

.

1. Do you know if it is breaking at the bottom, towards the top, or more or less in the middle? Is there any chance you have a picture of the damage? If I can somehow see or gauge specifically where they are splitting I can better tell you why.

.

2. What kind of RPMS are you running the engine at?

.

3. Were these actual brand new powerheads shipped from Mercury Marine? Or were they aftermarket, or rebuilt by some other company?

Customer: replied 11 months ago.

1 breaking in the middle no pictures, no camera 2 owner could not tell me 3 new power heads from merc we just changed them out ourselves and took the boat back to dealer to check out before we used the boat after the power head was replaced

Expert:  Jason replied 11 months ago.
When you say the owner could not tell you, what do you mean by that? Are you a mechanic working at the dealer? You are not the owner of this boat? What is the story there?
Customer: replied 11 months ago.

i am a engine builder this is a frend that i fish with some time i build all types of emgines but marine out boards if we caint figer ou whats going on if was any other type engine i would put a better rod in it

Expert:  Jason replied 11 months ago.

Here are the reasons why connecting rods break.

.

1. Engine over-reving. This is the #1 reason, which is why I had asked if you knew the full throttle RPMS on the engine

.

2. Engine overheat - But if there is no signs of gouging on the cylinder walls this is likely not the issue.

.

3. Lack of oil. - If this was the case the bearings would be smoked

.

4. Impact damage. If the propeller its a rock underwater, anything can and will break. Including a connecting rod.

.

5. Jumping the boat. This has a similar effect as an impact. What happens with the propeller leaves the water is the engine will wind right up to 8 or 9k rpms, and when the boats lands and the propeller grabs the water again. It is more likely when this happens to twist a propellershaft, and you can look at the propeller shaft to see if it is twisted at all. But like an impact, this can cause any shaft to snap, (the propeller or driveshaft) and it can cause the crankshaft to twist, and the connecting rods to snap.

.

6. A high speed hydrolock. This would be if the head gasket let go at high speed and the cylinder takes a big gulp of water. This typcially results in a smashed piston as well.

.

7. Plain old improper assembly from the start. If the crankshaft is not true, if the pistons are installed the wrong way, if the bearings are wrong. Any number of those things will cause it.

.

8. Lastly if the connecting rot was just defective from the start. If you look at the 2 mating surfaces where it broke. If you see pockets of air in the forging then that is a defective connecting rot.

.

Those are all the reasons why they will break. As to yours, you have to look at it and see if there is evidence of overheating and any other kind of damage. But 9 times out of 10, and especially if you can not see any other damage, the rod breaks because the engine is being over-reved. Wether that means it has the wrong propeller on it, and the RPMS are to high. Or somebody is just being stupid with it and reving it up in neutral. But when you over-rev these engines the connecting rods will snap every time.

Does that make sense?

Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 10011
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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