Slamming outboard(s) into reverse and hydrolocking the engine(s).

[rockyrude]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

I'd agree with Frank to the point of the gears being more vulnerable than the crank. I have to believe the gear ratio between the pinion and the driven gears would make it pretty hard to "drive backwards" to the crank. I also have to believe the momentary force on the con rods at the instant of fire is well beyond anything this scenario suggests. Now all we need to figure out is if hydro lock actually happened.

 

[Frank Acampora]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

There is no momentary force on the con-rods at the time of ignition. Lets say that these engines are loopers and fire about 18 degrees BTDC. The reason for advancing timing is that it takes time for the complete charge to burn. It is a controlled burn, not an explosion. For best efficiency and power it is necessary to have the burn time equal before and after TDC. Thus, when the charge ignites, there is a gradual pressure rise from about 150 PSI --compression ratio-- from start to finish of burn ( due to expanding heated gases) then it drops slowly as the piston continues to move down. Finally it drops to nominal zero as the exhaust valve opens. Average pressure-- Base Mean Effective Pressure (BMEP) is only about 300 PSI. (That's why it takes more cubic inches to make more torque--"There's no replacement for displacement") So, Con-rods (with the exception of racing rods) are NOT designed to withstand many thousands of pounds of compression force. Figure they only need to resist 1800 pounds on a 3 1/2 inch diameter piston then double that as a safety factor..

The damage (bent rods) is caused because other pistons are also moving. The whole mass has inertia in one direction and really, really, really does not want to reverse. The larger the mass and the faster it is spinning, the larger the inertia. Rapidly engage a prop spinning in the other direction and impulse loads far exceed the beam strength of the rods and they bend. Although, as I said before I would expect stripped gears or even a snapped shaft.

 

[Philster]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

I like this healthy discussion, which I why I posted this subject.

So, we are leaning in the direction of ''con rod bent because of forces other than hydrolock'' ?

 

[mla2ofus]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Are these Yamahas made in china?
Mike

 

[Ned L]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Again, very well stated Frank.

 

[steelespike]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

I can't speak directly to the outboad but a vintage style Chris Craft a friend had (1940's) Accidently slipped into neutral
at wot.
It did a severe dive so severe the water that washed over the bow broke both safety windshield panes and close to
filled the 3 passenger small cockpit.It would seem that an outboard would behave the same or close especially if some how jammed into reverse. Do these outboards have a reverse lock down that is active all the time or activates as shifted?
It would seem that the later style the motor might simply kick up before the shift lock ingages?
Sounds like some sort of "urban legend" like in 1956 when Chrysler had push button automatic transmissions.
People wondered what would happen if you put it in reverse at say 25 mph.My Math teacher did it and said it just went into reverse
and eventually backed up.
When I was about 14 at wot I cut the throttle on a 14 hp Evinrude, slammed it into reverse and gunned it.
No damage but it did stop in about 25 feet.Obviously not much speed involved. probably 21/22 mph.
I was cutting in front of a friend to beat him to a dock space A little stupid and scary thinking of it now.Boat did stop perfectly at the dock.

 

[BillP]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

I'm in the pure fantasia camp on this one too. Did this come from wiki?

bp

 

[Frank Acampora]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Fantasia? Maybe, maybe not. We don't know all the facts; we are just working on hearsay. However, under extreme conditions connecting rods will bend--true, that is uncommon damage, it doesn't happen every day, BUT it does happen. I only postulate a theory of why it may have happened based on available anecdotal "facts" and basic engine operating dynamics. Know the GIGO principle of computers? Garbage In Garbage Out. This might be a good one for Mythbusters.

 

[BillP]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Fantasia? Maybe, maybe not. We don't know all the facts; we are just working on hearsay. However, under extreme conditions connecting rods will bend--true, that is uncommon damage, it doesn't happen every day, BUT it does happen. I only postulate a theory of why it may have happened based on available anecdotal "facts" and basic engine operating dynamics. Know the GIGO principle of computers? Garbage In Garbage Out. This might be a good one for Mythbusters.

To each their own and nothing personal to anyone...If indeed this actually happened, I would say it falls into the defective parts category...or the rod was over compressed and stressed already from wave jumping or improper timing and happened to give when the throttle was chopped. Theory aside and short of seeing credible data, I think the whole situation is fantasy of the mind. Entertainment at best. Water getting into the cyl from the pickup intake by sudden stoppage just doesn't happen. Peace.

I quit watching Mythbusters when they stated an ultralight aircraft took flight by having the ground removed under it. They reported the wings had no air flow over them while a car pulled a "carpet" out from under the plane, keeping it from going forward. Pure BS. Air foils don't lift without air movement. I'm a pilot. Yes, there is much GIGO around.

bp

 

[cyclops2]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Well I do not know if Yamaha is having the same problems as Mercruiser has had over the years. TRUE LOW SPEED, HIGH VACUUM reversion, hydrolocking, with water in MANY cylinders. We had 2 old 454 engines replaced with new long blocks. To save some money the mechanic REUSED THE OLD WATER COOLED EXHAUST MANIFOLDS.

We got very lucky on the first trip. Hydrolocked both engines several times. I finally ordered the captains to run faster or slower than the problem rpms. ALL 8 cylinders were filled 1 time. Pull plugs. crank engine. Spray stops. blow off the plugs & we are running again. About 900 to 1200 rpms was the bad shifting speed. In a mid engined 40' woodie.

 

[smokeonthewater]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Folks, to pull the engine to neutral and then reverse while on plane would engage reverse gear at IDLE throttle and VERY likely stall the engine. Immediately after the engine stalled it would likely begin to rotate backwards from the torque created from dragging the prop through the water at speed.... If it was a 4 stroke, it would be very likely to pull water in through the exhaust.

 

[BillP]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Water coming back to the motor from the exhaust on inboards is nothing new and and not a motor mfg flaw. It's caused by improper exhaust design. Standpipes, tall risers and tail flaps are used to curb damaging backwash. I've even put seacocks on sailboat exhausts that can be shut when running in storm conditions. Basically, the exhaust pipe isn't tall enough to stay above the water and it floods straight into the cyls. It happens most often in rough weather and in hard backing down. I suppose really short distance installations could get flooded from the backwash which is the only way I can see an outboard getting water into the cyls. The motors don't suck water in, they are flooded from low elevation. Exhaust valves being open prevent vacuum sucking water, they don't create the suction in a running or sitting motor. Yamaha probably has a marginal exhaust baffle design that lets to the water in cyls when the backwash from stopping suddenly happens.

bp (disclaimer-my views are either right or wrong)

 

[Philster]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Let's regroup.

We are disregarding low-speed and common reversion issues associated with I/O engines, as there are thousands of cases of water reversion due to how the exhaust is designed (e.g., water not dumped far enough from engine) and/or how the cam timing creates overlap which results in a back-sucking action as the exhaust cycle finishes.

Back to O/B's:

There are a pretty fair number of cases of high-rpm to neutral panic maneuvers and/or high-rpm to nuetral/reverse maneuvers which resulted in bent con rods.

Now, whether this is due to water or other forces isn't clear. If I could see the engine and bent rods, I'd want to see water somewhere.

Was water found? No. Other forces contributed to con rod bending. Investigate and postulate causes.


Was water found? Yes. Investigate entry ways.

 

[F_R]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Well, since we don't have the original story here, all we are doing is guessing. So I might as well guess too. What kind of prop was he running? I'm guessing one of those go-faster ones where the exhaust flows OVER the hub rather than THROUGH it. I'm further guessing that when he hit reverse at high speed, the engine likely stalled. He now had a non-rotating prop being shoved through the water at 60MPH, which created a pile-up of water ahead of it. And that pile-up of water went right past the prop hub, and up the exhaust, into any exhaust valves that happened to be open. Then when he went to restart it, it wouldn't turn over because it was hydro-locked.

---OR----

Was it actually reported that the rods were bent, or is that a rumor that picked up with all the discussion. OK, lets say there were bent rods. In that case, the engine probably didn't stall when he hit reverse gear and throttle. But there wasn't enough exhaust pressure to keep that water from being pushed up the exhaust housing. So, it was forced into the exhaust valves, hydro-locking the piston, and flywheel inertia caused the locked ones to bend the rods. Race motors do that all the time when suddenly being submerged while running.

 

[cyclops2]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Horsepower sells more motors. SSOO

Everybody is now INCREASING valve timing OVERLAP Guess what happens ?? Even outboard motors CAN have enough overlap. Look how short the exhaust system is COMPARED to inboard engines. SUPRISE ??

Not really.

 

[jbjennings]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

interesting.

 

[Philster]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Horsepower sells more motors. SSOO

Everybody is now INCREASING valve timing OVERLAP Guess what happens ?? Even outboard motors CAN have enough overlap. Look how short the exhaust system is COMPARED to inboard engines. SUPRISE ??

Not really.

Valve overlap is a reality in many (maybe all)l Hi-Po engines; that is acknowledged. However, it muddies the water here to discuss it when camping with the water intrusion folks, because overlap only matters when water is present in small quantities (mere drops) and is sucked back during normal engine cycling. All that is moot because, if we are talking about hydrolock in these cases and not other forces, we are talking about voilent actions that caused a large amount of water to be forced into an engine regardless of overlap.. If the whole exhaust is getting a surge of water, valve overlap isn't a concern, because even without overlap (and it's sucking motion), a whole bunch o' water is getting forced into cylinders that have open exhaust valves (overlap not needed, just the normal cycle of 4-stroker).

Again, valve overlap is off the table; it's moot to discuss it here.

 

[F_R]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

I don't see how the clutch dog could possibly take the kind of stress you guys are discussing without shattering like glass. I would think it would be darned hard to actually get the clutch and gears to engage at wide open throttle without doing this. Am I mistaken?
JBJ

Sorry, I gotta laugh a bit. In my youth and wild days, I had a new Chevy Impala. I had always heard that you cannot shift an automatic transmission into reverse while going forward at any speed. Well one night I was more than slightly inebriated, so I tried it. Going about 35mph, I pulled it down into reverse. Sure enough, it shifted into reverse. I took it into the dealer the next morning for warranty repair. Needless to say, I didn't tell them what happened.

Not that that has anyting to do with clutch dogs.

BTW, I quit drinking since then. Just in case anybody wonders.

 

[jbjennings]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Dang F-R,
YOu're quite the experimenter.

 

[seahorse5]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

The hydrolocked 4-strokes with bent rods usually show a cam timing error code and often a MAP error code. Both are caused by reverse rotation of the motor where the cam sensor sees the pulley going backwards and the intake manifold gets pressurized and loses its normal vacuum when the intake valve becomes the exhaust valve and blow air into the intake manifold.

Several things have to happen in sequence for the hydrolocking to occur. While the motor is running in forward and the boat is moving at a good clip, the throttle is suddenly brought to idle and the motor shifted into reverse rapidly. The engine stalls from being pulled to idle and at the same time a reverse rotation load is put to the motor because of the boat's forward motion through the water is still turning the prop clockwise (in a std. rotation motor) and when slammed into reverse gear, the force against the prop from the water flow turns the stalled engine backwards. That opposite rotation of the motor triggers the cam sensor and possibly the MAP sensor, plus the exhaust valve now becomes an "intake valve" and puts a vaccum in the exhaust housing which sucks up water into the motor.

Like was explained, a series of events have to happen to cause the water ingestion and engine damage to a 4-stroke outboard. That's why it is not such a common occurance but the outcome is known in the outboard service industry and by a number of unfortunate boat owners.