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Old 28 July 2013, 14:32   #21
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I believe this can happen if the the throttle was yanked back to idle while still going forward at a good clip, then slammed into reverse hard. Like a panic situation in a near collision, throttle lever slammed from full ahead to full astern at speed. Normally in those cases where the motor dies and when shifted into reverse, the force of the water from the forward boat motion pushes against the propeller and causes the motor to rotate backwards. That sucks up water through the exhaust valve which is now acting as an intake valve while rotating backwards, thus bending rods and locking up the motor. 2 stroke would do the same thing. Its fairly rare, but can happen. But as everyone say, it is Operator error!
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Old 28 July 2013, 17:40   #22
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Originally Posted by Robbie Diesel View Post
I believe this can happen if the the throttle was yanked back to idle while still going forward at a good clip, then slammed into reverse hard. Like a panic situation in a near collision, throttle lever slammed from full ahead to full astern at speed. Normally in those cases where the motor dies and when shifted into reverse, the force of the water from the forward boat motion pushes against the propeller and causes the motor to rotate backwards. That sucks up water through the exhaust valve which is now acting as an intake valve while rotating backwards, thus bending rods and locking up the motor. 2 stroke would do the same thing. Its fairly rare, but can happen. But as everyone say, it is Operator error!
Possible in theory, assuming you actually manage to get it to go into reverse. You're as likely to smash the gearbox. You'd still have to be moving at a fair speed to do it at the point it went into reverse.
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Old 28 July 2013, 19:22   #23
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Quote:
Originally Posted by Robbie Diesel View Post
I believe this can happen if the the throttle was yanked back to idle while still going forward at a good clip, then slammed into reverse hard. Like a panic situation in a near collision, throttle lever slammed from full ahead to full astern at speed. Normally in those cases where the motor dies and when shifted into reverse, the force of the water from the forward boat motion pushes against the propeller and causes the motor to rotate backwards. That sucks up water through the exhaust valve which is now acting as an intake valve while rotating backwards, thus bending rods and locking up the motor. 2 stroke would do the same thing. Its fairly rare, but can happen. But as everyone say, it is Operator error!
I'm doubtful of this .. The engine always puts out positive pressure to he exhaust regardless of gear position when it's running

This looks like a submerged motor in some shape or form
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Old 28 July 2013, 19:30   #24
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I'm doubtful of this .. The engine always puts out positive pressure to he exhaust regardless of gear position when it's running

This looks like a submerged motor in some shape or form
The theory is, engine stalls when it's slammed into reverse, and in reverse the prop doesn't ratchet so the motor is forced to turn backwards making the exhaust stroke an inlet stroke sucking water up.

You'd have to be really moving to do it though, and you'd have to smash it into reverse.

It doesn't look like it's been submerged-there's no corrosion anywhere apart from those top 2 pistons.
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Old 29 July 2013, 00:35   #25
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All this theorising makes me laugh. The fact of the matter is it happened, and only last weekend. The pictures were taken on Tuesday last week as the unit was stripped down. I was there, water was forced up the exhaust and in fact this appeared on another forum.

Yamaha + Panic stop from high speed =

######

I can definitely see water ingestion through the exhaust ports as a cause for failure.. Many 4 stroke engines (especially those with variable cam timing) have a tendency to actually suck air back into the exhaust port for a split second between exhaust pulses, or, on deceleration if the camshaft advances to keep emissions down while there is no load. A few automakers have done away with EGR valves, and actually use exhaust cam timing/phasing to suck air/exhaust back in on deceleration. So, if he jumped off of plane quickly, I could see water surrounding the exhaust ports on the back of the cowling, and flooding the engine. This would hydrolock the motor, and either bend or break connecting rods, wrist pins, or pistons..

######

The power head has been replaced under warranty, so owner is lucky. The engine hydro locked and resulted in the damage. There was also an article in the RNLI offshore section which talked about the work the RNLI do adapting outboards by fitting exhaust flaps to prevent water ingress when submerging. Such devices do not come as standard!

The estimated cost of the rebuild was >6k. So be warned, stopping to quickly in a straight line can be hazardous to your engine's health and your pocket. I was taught this very early on in my boating career and told that just what happened here can happen!
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Old 29 July 2013, 01:42   #26
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And basic physics says that even a total vacuum for a split second wouldn't be able to suck enough water back up the leg for it to reach the cylinders. It's simply not possible. The 'tendency to suck air back in' refers to millimetres of air, nowhere near enough to suck water up the exhaust.

The RNLI exhaust flaps are absolutely nothing to do with what you're saying-they are for inversion/submersion proofing, not so they can shut the throttle at high speed.

I'm not debating that hydraulic locking the motor would do that damage-it can,it will and it has (hence your pics). I'm arguing that the guy who was driving has done something a bit more extreme than shutting the throttle at speed in a straight line. I strongly suspect he's smashed it into reverse as well and it's spun up backwards.
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Old 29 July 2013, 02:35   #27
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Hondas have this issue, if the engine is hanging low on the transom then when the boat is fully loaded etc then you have to be careful not to stop the engine without trimming up a bit, also when starting you must be sure to keep the starter turning until the engine fires, the danger is that if the engine stops near TDC then falls back from TDC then the piston can act as a pump drawing water into the lower cylinders...
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Old 29 July 2013, 02:48   #28
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And basic physics says that even a total vacuum for a split second wouldn't be able to suck enough water back up the leg for it to reach the cylinders. It's simply not possible. The 'tendency to suck air back in' refers to millimetres of air, nowhere near enough to suck water up the exhaust.

The RNLI exhaust flaps are absolutely nothing to do with what you're saying-they are for inversion/submersion proofing, not so they can shut the throttle at high speed.

I'm not debating that hydraulic locking the motor would do that damage-it can,it will and it has (hence your pics). I'm arguing that the guy who was driving has done something a bit more extreme than shutting the throttle at speed in a straight line. I strongly suspect he's smashed it into reverse as well and it's spun up backwards.

I am sure there is more to this than has been divulged by the owner and the engineer also reckons that is the case. I did not say the RNLI fitted the flaps so they could shut the throttle at high speed, just pointing out that they use them to prevent water backing up the exhaust and yes, during inversion .

The damage is self evident, how it really happened will never be known as people lie! The engineers had another outboard, Suzuki, fitted to a Hardy that was also being stripped down and found to have water inside, this also looks as if its been dunked, but owner is not telling the full story.
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Old 29 July 2013, 03:52   #29
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I'm doubtful of this .. The engine always puts out positive pressure to he exhaust regardless of gear position when it's running

This looks like a submerged motor in some shape or form
I agree that there is always positive pressure when the engine is running, but if the powerhead is rotated backwards via the prop, then it will try to suck up the exhaust & exhaust through the air intake but of course water cannot be compressed & major damage occurs.

Google "Yamaha water Ingestion" & you will see that it can happen. Very rare, but a few cases of Yam & Hondas destroyed from panic stopping by slamming full ahead to reverse at speed. It can happen to any outboard.

But its not really the manufacturers fault. It does state in the manual that the boat should be stationary when shifting F-N-R. Its a bit like expecting a car manufacturer to pay out warranty if a car was doing 100mph & thrown into 1st gear & destroys the engine. Hardly a manufacturer defect is it? LoL
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Old 29 July 2013, 05:31   #30
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stopping quickly water up the exhaust ,yep seen it before.
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