Impeller wedge in liner 2010 Mercury 60/40

[Scott 1752]

Hey guys,

While running on plain I lost everything motor cut out crank but would not fire. After inspection the impeller came down and wedged in the liner. I pulled the foot, and impeller off, reinstalled, and checked for proper clearance. Put boat back in water ran fine at 3k as soon as I gunned it to get on plain the same thing happened. Pulled jet unit off found no visual issues with shaft or excess play. Any idea what causes the impeller to travel down into the liner and get wedged like that?

 

[tdonoughue]

Hmmm.

Swollen liner was my first thought, but that would scrape all of the time.

If it is wedged into the liner, must be that the shaft is not straight. At high RPM, as soon as you hit the harmonic, that will bend the shaft. Only thing of which I can think (assuming your checks on play, etc. are correct--at high RPM, forces on all of those will be magnified as well...).

 

[Scott 1752]

Hmmm.

Swollen liner was my first thought, but that would scrape all of the time.

If it is wedged into the liner, must be that the shaft is not straight. At high RPM, as soon as you hit the harmonic, that will bend the shaft. Only thing of which I can think (assuming your checks on play, etc. are correct--at high RPM, forces on all of those will be magnified as well...).

Thank you for the reply. Visually the shaft doesn’t look bent as I pulled the lower unit off and attempted to inspect it for any damage. It was almost as the shaft slid down when the impeller got wedged as evident by play in the impeller after the event.

I’ve put everything back together, set clearances, and ensured good seating on nut and tab washer. Ran it on idle with the hose for a good 10 minutes and everything sounds beautiful. I plan to test it out on the water tomorrow

How does bending the shaft happen and how would I check for certain? I’m not to clear on hitting the harmonic? I was probably around 5000~5200 rpm when the event happened and had no indications of a problem beforehand nor did I hit anything or evidence of sucking something into the jet.

 

[diehard]

is there a lock tab on the impeller nut?

 

[Scott 1752]

is there a lock tab on the impeller nut?

Yes. I went ahead and put a new one on. Same result. It’s fine until I get it up to around 4000 then the impeller gets wedged

 

[diehard]

maybe remove one shim on top?

 

[Scott 1752]

I would lean to that if I had recently done any adjustments to the shims but I hadn’t. It was maybe a 4mo old liner and ss impeller with plenty of hours. Tried swapping to a spare aluminum impeller and liner but same result.

Maybe there’s a shaft or bearing cone issue? I may just have to wait until next week and give outboard jets a call for recommendation.

 

[diehard]

let us know what you find,good luck

 

[tdonoughue]

How does bending the shaft happen and how would I check for certain? I’m not to clear on hitting the harmonic? I was probably around 5000~5200 rpm when the event happened and had no indications of a problem beforehand nor did I hit anything or evidence of sucking something into the jet.

Oh, I have no idea. I'm sure you could suck up something extreme enough that would do it.

Problem is it would not take a lot of bend. No idea how to check beyond pulling the impellers off the shaft and trying it against a true surface (even then, would be tough with the end spines). Harmonics would enter in because a the frequency of the wobble of the shaft would match with the RPM so that happens at the same point in rotation. As RPM increases, so will the force on the shaft. When the harmonics kick in, rather than the shaft bending itself and then bending in another position as it wobbles back, it would bend to the same position (and I am guessing that is why at higher RPM you are getting it wedged--when those harmonics hit you get more wobble and it hits the side).

But you mention that the 'shaft slid down'. If there was no play in the shaft and the shaft was not bent, when the impeller was embedded in the ring, how did that ... work? Something had to be off, out, or something or the impeller would not be able to hit, right? Do you have a pick of it embedded?

 

[Neutron]

Oh, I have no idea. I'm sure you could suck up something extreme enough that would do it.

Problem is it would not take a lot of bend. No idea how to check beyond pulling the impellers off the shaft and trying it against a true surface (even then, would be tough with the end spines). Harmonics would enter in because a the frequency of the wobble of the shaft would match with the RPM so that happens at the same point in rotation. As RPM increases, so will the force on the shaft. When the harmonics kick in, rather than the shaft bending itself and then bending in another position as it wobbles back, it would bend to the same position (and I am guessing that is why at higher RPM you are getting it wedged--when those harmonics hit you get more wobble and it hits the side).

Its definitely not that complicated. Shaft is most likely walking rearwards and jamming the impeller, it needs to be completely disassembled to find the culprit, like a snap ring or bad bearing. Without knowing how the assembly is i really dont know. But have seen this in older pumps.

To the op, to take the pump off and reinstall Without finding the problem is a waste of time. Something caused the lockup and it doesn't happen for no reason. And then it happens again. Time for a complete pump overhaul. Make your effort productive not wasteful.
You can take it off and set it 100 times and you will have the same result

 

[Scott 1752]

Oh, I have no idea. I'm sure you could suck up something extreme enough that would do it.

Problem is it would not take a lot of bend. No idea how to check beyond pulling the impellers off the shaft and trying it against a true surface (even then, would be tough with the end spines). Harmonics would enter in because a the frequency of the wobble of the shaft would match with the RPM so that happens at the same point in rotation. As RPM increases, so will the force on the shaft. When the harmonics kick in, rather than the shaft bending itself and then bending in another position as it wobbles back, it would bend to the same position (and I am guessing that is why at higher RPM you are getting it wedged--when those harmonics hit you get more wobble and it hits the side).

But you mention that the 'shaft slid down'. If there was no play in the shaft and the shaft was not bent, when the impeller was embedded in the ring, how did that ... work? Something had to be off, out, or something or the impeller would not be able to hit, right? Do you have a pick of it embedded?

Thanks for circling back on this one. No i hadn’t taken a picture, and now I have the jet pump removed.

I was hoping the issue would be evident when parts were removed.

Its definitely not that complicated. Shaft is most likely walking rearwards and jamming the impeller, it needs to be completely disassembled to find the culprit, like a snap ring or bad bearing. Without knowing how the assembly is i really dont know. But have seen this in older pumps.

To the op, to take the pump off and reinstall Without finding the problem is a waste of time. Something caused the lockup and it doesn't happen for no reason. And then it happens again. Time for a complete pump overhaul. Make your effort productive not wasteful.
You can take it off and set it 100 times and you will have the same result

You’re correct it was a waste of time. I have it disassembled again and won’t be going back on until a complete pump overhaul. Thanks for the advice. I’ll post a few photos for the next newbie

 

[Neutron]

Definitely post some pics! That makes it easier to understand what you are dealing with and possibly for us to help

 

[tdonoughue]

Thanks, @Neutron. Clearly I'm not familiar enough with this jet... Was thinking that it was like mine, but that would be a no.

Looking forward to the pics and more learning.