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Yamaha F150 cracked piston

Old 06-05-2020, 08:39 AM
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Default Yamaha F150 cracked piston

My friend was riding in his KW the other day. It has a 3 year old, 110 hour F150. New plugs and oil within a month ago. Running great for several days of use, all of a sudden on that day while on plane the motor stutters and quits. He can start it, smokes like hell, and he has to limp home. Fuel is perfect, no water. Couple days later dealer does compression tests and one cylinder at zero. Looks inside and piston is cracked. Absolutely no warning. Anyone ever heard of anything like that? Luckily it looks like it might get covered under a YES warranty.
Old 06-05-2020, 08:50 AM
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Not unheard of. Detonation is typically what does it.

Although detonation damage is typically not covered by either a warranty or the YES contract, I suspect that Yamaha will fix it on their dime. Goodwill.

It might be helpful to your friend to make sure that the motor has a propeller on it that will let the motor turn at or near 6000 RPM when the boat is loaded. Engine trimmed up only to the point of best speed and no further. Make sure that the gasoline is fresh and not allowed to get stale. 110 hours on a 3 year old motor tells me that old gasoline might have been used. Just a guess.
Old 06-05-2020, 10:29 AM
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...or stop running cheap 87 octane.
Old 06-05-2020, 12:17 PM
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He actually bought the boat a year or so ago and it only had around 30 hours on it. He’s put the other 80 on it this year. Alway non-ethanol, first thing I asked. Tech mentioned something about fuel/air mix sensors being way out of range.
Old 06-05-2020, 05:56 PM
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Originally Posted by alloyboy View Post
Not unheard of. Detonation is typically what does it.

Although detonation damage is typically not covered by either a warranty or the YES contract, I suspect that Yamaha will fix it on their dime. Goodwill.

It might be helpful to your friend to make sure that the motor has a propeller on it that will let the motor turn at or near 6000 RPM when the boat is loaded. Engine trimmed up only to the point of best speed and no further. Make sure that the gasoline is fresh and not allowed to get stale. 110 hours on a 3 year old motor tells me that old gasoline might have been used. Just a guess.

If I'm trimmed up I get 6k on my prop, am i doing damage to my engine if I am running wide open and fully trimmed down? With the prop not spinning at 6k?
Old 06-05-2020, 06:52 PM
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Any engine with 300 hrs and a good maintenance record should never have this happen .. If the fuel was non ethanol and stabilized at the end of the season that isn't the problem. I have 3 boats with different outboards and never had any issues described with a 150 Yamaha 4 stroke, ,90 HP Yamaha 2 stroke ,or a 40hp 4 stroke Yamaha. They are all stored for 6mos a yr.,One in the south and others in the NE. I rarely put 100 hrs each on these motors and they run to perfection. They are propped properly and can run to max WOT. Something elsr is going on. There isn't enough info to try and figure it out,but it should be a valid warranty claim.
Old 06-05-2020, 06:57 PM
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By the way, which piston is cracked? #2 and #3 Are most likely.

Has the head been removed? Any other damage noted?
Old 06-05-2020, 07:46 PM
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Originally Posted by polliwog 42 View Post
Any engine with 300 hrs and a good maintenance record should never have this happen .. If the fuel was non ethanol and stabilized at the end of the season that isn't the problem. I have 3 boats with different outboards and never had any issues described with a 150 Yamaha 4 stroke, ,90 HP Yamaha 2 stroke ,or a 40hp 4 stroke Yamaha. They are all stored for 6mos a yr.,One in the south and others in the NE. I rarely put 100 hrs each on these motors and they run to perfection. They are propped properly and can run to max WOT. Something elsr is going on. There isn't enough info to try and figure it out,but it should be a valid warranty claim.
Why exactly would non ethanol fuel with stabi from last year still not be possibly bad? Why would ethanol fuel cause this? until the root cause is determined, guesses are just that...a guess, 300 hours makes no difference "shit happens" at anytime, when a motor is new, or when it's years old, even when it's 300 hours old, things go wrong.
Old 06-05-2020, 08:21 PM
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Would like to see pics of the piston damage. A cracked piston doesn’t really tell us much. Typical detonation damage occurs at the piston outer periphery resulting in melted or cracked ring lands. Would find it odd that there was no other warning prior to it letting loose if there was a a lean condition or poor fuel causing detonation. Bad detonation/pinging sounds like marbles in your motor up until the bad sh*t happens.

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