Impeller questions

[NGranneman]

Was boating with my 2014 yamaha 210sx this weekend and all of a sudden my left engine would sound off if i attempted to go over 4-5000 rpm. I kept it at 3-4000 rpm to get back to my lift around 2 miles away and engines sounded normal during this part. Tried to rev it up a couple times and do reverse to clear suspected debris but didn’t do anything. Once i got it on my lift I pulled a 2-3 mm rock type substance that seemed wedged between impeller and side along with small 1 inch stick that didn’t really feel stuck. Took it back out and seems to be working fine now. Couple questions as this first time this has happened to me

1) Sound like from debris above or something else I should look into?
2) Why if it is debris seems to do fine below certain rpm?
3) Any damage should be concerned about from driving back at the lower rpm or trying to rev it out a couple times?

 

[FSH 210 Sport]

Was boating with my 2014 yamaha 210sx this weekend and all of a sudden my left engine would sound off if i attempted to go over 4-5000 rpm. I kept it at 3-4000 rpm to get back to my lift around 2 miles away and engines sounded normal during this part. Tried to rev it up a couple times and do reverse to clear suspected debris but didn’t do anything. Once i got it on my lift I pulled a 2-3 mm rock type substance that seemed wedged between impeller and side along with small 1 inch stick that didn’t really feel stuck. Took it back out and seems to be working fine now. Couple questions as this first time this has happened to me

1) Sound like from debris above or something else I should look into?
2) Why if it is debris seems to do fine below certain rpm?
3) Any damage should be concerned about from driving back at the lower rpm or trying to rev it out a couple times?

Did you visually inspect the pump, impeller and wear sleeve?

 

[NGranneman]

Did you visually inspect the pump, impeller and wear sleeve?

Yes, once I got it on my lift I looked under through the grate and saw the very small hard-like pebble that appeared located between the impeller and sleeve. Seemed to flake out easy. Didn't see any wear/tear on the impeller or sleeve. Also found a small stick from reaching in blindly in area I couldn't see and I couldn't tell if it was stuck anywhere or not

 

[JoshNeuman]

Was boating with my 2014 yamaha 210sx this weekend and all of a sudden my left engine would sound off if i attempted to go over 4-5000 rpm. I kept it at 3-4000 rpm to get back to my lift around 2 miles away and engines sounded normal during this part. Tried to rev it up a couple times and do reverse to clear suspected debris but didn’t do anything. Once i got it on my lift I pulled a 2-3 mm rock type substance that seemed wedged between impeller and side along with small 1 inch stick that didn’t really feel stuck. Took it back out and seems to be working fine now. Couple questions as this first time this has happened to me

1) Sound like from debris above or something else I should look into?
2) Why if it is debris seems to do fine below certain rpm?
3) Any damage should be concerned about from driving back at the lower rpm or trying to rev it out a couple times?

That is exactly how jet pumps behave when they ingest something. You handled the situation perfectly by limping it back at a safe speed.

To answer your questions directly:

1) Was it the debris?Yes, 100%. The clearance between the impeller blades and the wear ring on those Yamahas is incredibly tight. Even a tiny 2-3mm rock wedged in the wrong spot disrupts the water flow and causes cavitation. When a jet pump cavitates, it sounds like there are marbles rattling around in your engine or like a horrible grinding noise.

2) Why was it fine at low RPM?At lower RPMs (3-4000), the impeller isn't spinning fast enough to create a massive pressure differential. The water flows around the debris without too much issue. But as soon as you push past 5000 RPM, the pump tries to move a huge volume of water. The rock disrupts that suction, causing the water pressure to drop so low that it literally boils (cavitation). That sudden loss of thrust and violent collapsing of air bubbles is what creates that awful sound and vibration at higher speeds.

3) Is there any damage to worry about?You don't need to worry about driving it back at 3-4k RPM—keeping it at a speed where the engine sounded normal and wasn't vibrating was the exact right move. Trying to rev it or blast it out in reverse is also the standard first-line troubleshooting step on the water.

The only thing you should do next time it's on the lift is grab a flashlight and look up through the intake grate. Check the leading edges of the impeller blades and the wear ring (the housing around the blades) for any deep gouges. A 2-3mm rock will usually just leave a minor scratch, which is completely fine and won't affect performance. Since it is running smoothly now, you are good to go!

 

[NGranneman]

Thanks for all the detail. Any other tricks on trying to clear it out while on the water outside of checking access ports, revving it up, and trying reverse?

What is still a little confusing to me is if the impellar that has the object in it is still spinning at the 3-4000 RPM or is the rock stopping it from spinning and if it isn't spinning then how are you getting any type of performance that allows it to limp along?

That is exactly how jet pumps behave when they ingest something. You handled the situation perfectly by limping it back at a safe speed.

To answer your questions directly:

1) Was it the debris?Yes, 100%. The clearance between the impeller blades and the wear ring on those Yamahas is incredibly tight. Even a tiny 2-3mm rock wedged in the wrong spot disrupts the water flow and causes cavitation. When a jet pump cavitates, it sounds like there are marbles rattling around in your engine or like a horrible grinding noise.

2) Why was it fine at low RPM?At lower RPMs (3-4000), the impeller isn't spinning fast enough to create a massive pressure differential. The water flows around the debris without too much issue. But as soon as you push past 5000 RPM, the pump tries to move a huge volume of water. The rock disrupts that suction, causing the water pressure to drop so low that it literally boils (cavitation). That sudden loss of thrust and violent collapsing of air bubbles is what creates that awful sound and vibration at higher speeds.

3) Is there any damage to worry about?You don't need to worry about driving it back at 3-4k RPM—keeping it at a speed where the engine sounded normal and wasn't vibrating was the exact right move. Trying to rev it or blast it out in reverse is also the standard first-line troubleshooting step on the water.

The only thing you should do next time it's on the lift is grab a flashlight and look up through the intake grate. Check the leading edges of the impeller blades and the wear ring (the housing around the blades) for any deep gouges. A 2-3mm rock will usually just leave a minor scratch, which is completely fine and won't affect performance. Since it is running smoothly now, you are good to go!

 

[FSH 210 Sport]

Thanks for all the detail. Any other tricks on trying to clear it out while on the water outside of checking access ports, revving it up, and trying reverse?

What is still a little confusing to me is if the impellar that has the object in it is still spinning at the 3-4000 RPM or is the rock stopping it from spinning and if it isn't spinning then how are you getting any type of performance that allows it to limp along?

The best thing to do is stay in deeper water than you were to avoid sucking up a rock.

The impeller is still spinning, if it was not the engine would not be running. The reason that the impeller with the stone was cavitating is because the stone was destroying the laminar flow of water on the impeller and made it cavitate. Cavitation is caused by a pressure differential between the front and back sides of the impeller that exceeds ability of the water to stay attached to the back sides and is replaced by a vacuum induced air space.

As @NGranneman said, you’re all good now which is great! Get out there and burn some fuel and avoid operating in water less than 3’.

 

[NGranneman]

The best thing to do is stay in deeper water than you were to avoid sucking up a rock.

The impeller is still spinning, if it was not the engine would not be running. The reason that the impeller with the stone was cavitating is because the stone was destroying the laminar flow of water on the impeller and made it cavitate. Cavitation is caused by a pressure differential between the front and back sides of the impeller that exceeds ability of the water to stay attached to the back sides and is replaced by a vacuum induced air space.

As @NGranneman said, you’re all good now which is great! Get out there and burn some fuel and avoid operating in water less than 3’.

Think the cavitation is making more sense. So the impeller has the rock attached to it and the rock is rotating with the impeller and causes the pressure differences leading to cavitation? If the foreign object is too big and doesn't allow the impellers to move then that would stop the engine?