Ran across rock bed today with jet boat

[danclemo]

Well, was on a new lake yesterday and didn't know there was a low area with small rocks. Of course, wasn't paying attention either at the time talking to wife/kids and went right through a rock garden. Sucked up rocks and damaged impeller to where it's frozen. I know I'm out impeller and wear sleeve are toast. Whats the history on engine damage for doing something this stupid? Curious if I could have damage lower end of motor, do they have any type of shear pin/key similar to prop motors that would save me? Curious how much $$ I'm out.

 

[Julian]

I sucked up a baseball size rock with no damage.... It all depends on how long they were in there.

 

[malibu Dan]

I’ve done the same.. rock ruined impeller .. new impeller no problem since..

 

[haknslash]

Don't see how you would ruin the engine. The cooling intake grate in the jet pump has super small holes so I doubt anything of size would make it through.

When you say your impeller is frozen do you mean there are still rocks wedged between it and the wear ring or that the blades got so torn up they are stuck or embedded into the wear ring?

 

[Bruce]

I doubt that you did any engine damage.

Pull the pump, start the engine and see if she purrs. Don't rev highly. The RPMS will shoot through the roof when you move the throttle without the water load.

This video shows how to pull the pump https://jetboaters.net/threads/yamaha-jet-pump-disassembly-from-grant-browne-youtube.446/

I pulled a friends pump at the boat ramp removed a large crystal reinstalled the pump and he went back to surfing.

 

[swatski]

Don't see how you would ruin the engine.

I do not believe Yamaha jet boat engines are ruined when stalled by impeller obstruction, it happens all the time. But
There was discussion about it and if stalling an engine ruins it, like in airplanes (piston engines that is, not turbo props - those are definitely ruined when stalled by anything but running out of fuel).

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[swatski]

Well, was on a new lake yesterday and didn't know there was a low area with small rocks. Of course, wasn't paying attention either at the time talking to wife/kids and went right through a rock garden. Sucked up rocks and damaged impeller to where it's frozen. I know I'm out impeller and wear sleeve are toast. Whats the history on engine damage for doing something this stupid? Curious if I could have damage lower end of motor, do they have any type of shear pin/key similar to prop motors that would save me? Curious how much $$ I'm out.

I would pull the pump and check things out.
Those engines stall like a car engine when you release your clutch too quickly with not enough gas. Should be no problem. Other than your impeller and perhaps wear ring is likely damaged.

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[danclemo]

Thanks everyone. Dropped off at marina and should hear back in week or two. Hoping just impeller is jammed and not damage to engine. Tech told me could have damaged Con Rod, but won't know until he gets impeller freed and inspected.

 

[YamahaCC]

The big question is how fast were you going when the engine 'jammed'? Idle speed is no big deal, but if you went from 7k to 0k instantly engine damage may have happened, rods can get bent when that happens.

 

[Cobra Jet Steering LLC]

The engine and pump have a coupler between them with rubber vibration dampener compound in between the two sides of the coupler .
Can you damage an engine doing what you did, possibly yes but doubtful .
You can do more damage running a cold engine really hard without warming it up, or revving one with no load on it.
Like others have said pull the pump and see if the engine will run.

 

[Bruce]

This outcome is unfortunate. Two weeks without a boat and likely a big bill when the owner likely could have pulled and reinstalled the pump within a few hours, potentially with the assistance of a big hammer.

 

[Scottintexas]

Thanks everyone. Dropped off at marina and should hear back in week or two. Hoping just impeller is jammed and not damage to engine. Tech told me could have damaged Con Rod, but won't know until he gets impeller freed and inspected.

Is your marina a Yamaha dealer or do they work on jetski's? I worry that he is even thinking engine possibilities when I don't ever recall somebody posting about blowing an engine by stalling it either by rope or debris

 

[DBamaC]

I doubt that you did any engine damage.

Pull the pump, start the engine and see if she purrs. Don't rev highly. The RPMS will shoot through the roof when you move the throttle without the water load.

This video shows how to pull the pump https://jetboaters.net/threads/yamaha-jet-pump-disassembly-from-grant-browne-youtube.446/

I pulled a friends pump at the boat ramp removed a large crystal reinstalled the pump and he went back to surfing.

Bruce, you mentioned a gasket in the link you attached. I sucked up some wood earlier in the season. I pulled the pump and removed the debris, inspected the impeller and wear ring (looked pretty good) and reassembled...no gasket or sealant. Didn't think about it at the time. Due to family issues, I've only been back out twice since then.

The first time back out I was making a little lower than normal rpm's and my top speed was down about 10 mph (5 adult occupants). Before I went out the second time I pulled the plugs, checked the gaps (were a little tight) and reinstalled as they were new in May, only 10 or 15 engine hours ago. Got on the lake, same thing...top rpm's were just over 7K and top speed a little under 40 (6 adult occupants). My son was driving and I (oddly) was sitting in the center of the rear seat. The amount of water coming up on my back was way more than normal...enough mist in the air to wet the back of my shirt. Gave me something to think about on the drive home.

I'm thinking the lack of seal at the impeller is my entire issue. I've read some on syptoms of a failed SC clutch and my issues are not as severe as what's described (top speed in the 30's for a ski and rpm's in the low 6k range). I really don't think my impeller looked bad enough to cost me 10 mph and wouldn't explain the loss in engine speed (links to pics below from my post when I pulled the plug). I surmise the slight loss in engine speed is inefficiency being cause by the lack of pressue at the impeller.

Thoughts?

https://jetboaters.net/attachments/3a432e54-ba27-4809-a01b-497a88405fd7-jpeg.74799/
https://jetboaters.net/attachments/86e77b84-74a5-4182-a846-221b0fa6b1ee-jpeg.74800/

 

[Bruce]

@DBamaC, I am not sure what max RPM should be for your boat but if you have lost RPM it is not a pump inefficiency problem. When the pump is cavitating or not sealed properly the engine will rev higher or at least higher that it should for the amount of throttle.