WTF!!!!!

[bronze_10]

So @swatski... Let's say for example the impellers are the issue, which is appears they are, and they are out of spec.. He did say he was stuck on a sand bar once. How much sand would need to run through his motors to sand down all the edges of the impeller to get it that far out of spec?.. On both engines gonna bran new boat? Unless I am missing something or reading too much in between the lines its seems very uniformly out of spec. I know it is almost unheard of but could this have been an improper sizing issue from the factory?

 

[Gym]

@John Mcpartland, I see from your previous posts you sucked up a rope in Sept 2017. You mentioned the rope melted then hardened to the shaft so I'm guessing it ran for a couple of minutes before you detected the problem. You must have damaged the smooth fiberglass tunnel as you stated that you covered the tunnel with 3M 4200. Did you start having problems after that? The tunnel needs to be a smooth surface to provide a laminar flow of water to the impeller to prevent cavitation. I don't think 4200 would allow for a smooth flow.

Did you change out or have any work done to the impellers such as straightening or repitching? Are there a lot of scratches on the pump liners from the sand bar incident? Does your boat pull to one side while running at the same RPM on both engines? I'm thinking this may be a one sided problem rather than both sides. Can you shoot us a pic of the tunnel you repaired?

 

[haknslash]

Aren't the 19' impellers a different size than the other boats? If they're smaller I wonder if the factory somehow installed the wrong spec impeller(s)?

 

[swatski]

So @swatski... Let's say for example the impellers are the issue, which is appears they are, and they are out of spec.. He did say he was stuck on a sand bar once. How much sand would need to run through his motors to sand down all the edges of the impeller to get it that far out of spec?.. On both engines gonna bran new boat? Unless I am missing something or reading too much in between the lines its seems very uniformly out of spec. I know it is almost unheard of but could this have been an improper sizing issue from the factory?

Absolutely. Yamaha has on occasion installed wrong impellers, maybe not so much in recent years as they have stopped providing impellers with different pitch for the two sides.
It is relatively easy to bend trailing edges, even a slight bend will change the OD of those long blades. Has that happened here? I'm not sure.
@Gym's points above are valid, and with all the signs pointing to excessive cavitation it has got to be a tunnel leak(s) and/or impeller issue.

--

 

[swatski]

@John Mcpartland, I see from your previous posts you sucked up a rope in Sept 2017. You mentioned the rope melted then hardened to the shaft so I'm guessing it ran for a couple of minutes nefore you detected the problem. You must have damaged the smooth fiberglass tunnel as you stated that you covered the tunnel with 3M 4200. Did you start having problems after that? The tunnel needs to be a smooth surface to provide a laminar flow of water to the impeller to prevent cavitation. I don't think 4200 would allow for a smooth flow.

Did you change out or have any work done to the impellers such as straightening or repitching? Are there a lot of scratches on the pump liners from the sand bar incident? Does your boat pull to one side while running at the same RPM on both engines? I'm thinking this may be a one sided problem rather than both sides. Can you shoot us a pic of the tunnel you repaired?

@John Mcpartland I think @Gym could be right. One quick way to check would be - if you push the boat with one engine at the time - what happens? Leave one engine in idle and WOT/hard start/ride with the other - only - you should be able to see if there is a difference. The boat should easily reach 15-20mph running on a single engine. If it does not, that would be further evidence of cavitation.
You may have a lot of damage in one and a little bit in the the other but enough that both hit the rev limiter (at 7,900 RPM). Isolating the engines for testing may help diagnose the problem quicker.

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[swatski]

Aren't the 19' impellers a different size than the other boats? If they're smaller I wonder if the factory somehow installed the wrong spec impeller(s)?

The diameter is the same but the impellers are quite different, the 19' actually have longer blades (and would cavitate less - all else being equal).
SOme guys running at altitude found that out and actually use those (190 style impellers) in twins - for better hole shot. @Williamsone46 pointed that out, if I remember correctly.
A partial part number is always stamped on the stem of those OEM impellers so it should be easy to rule it out. I doubt that is the issue here though.

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[Williamsone46]

The diameter is the same but the impellers are quite different, the 19' actually have longer blades (and would cavitate less - all else being equal).
SOme guys running at altitude found that out and actually use those (190 style impellers) in twins - for better hole shot. @Williamsone46 pointed that out, if I remember correctly.
A partial part number is always stamped on the stem of those OEM impellers so it should be easy to rule it out. I doubt that is the issue here though.

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The 6CW used in the 190's is the same size OD but has more over lap in the blades, better for high elevation.

 

[Williamsone46]

@John Mcpartland I haven't seen anyone ask or you say but what kind of rpm's are you turning?

Is one motor turning more or less and by how much? It's unlikely that both impellers if damaged were damaged equally.

 

[MidnightRider]

@John Mcpartland I haven't seen anyone ask or you say but what kind of rpm's are you turning?

Is one motor turning more or less and by how much? It's unlikely that both impellers if damaged were damaged equally.

Mentioned briefly in opening post but not sure if that was both engines, assume so.

Fastforward to today, we had 5 adults ( the largest,me at 208) and 5 kids under 12 and the couldn't get above 16mph at 8k rpm.

 

[John Mcpartland]

@John Mcpartland I haven't seen anyone ask or you say but what kind of rpm's are you turning?

Is one motor turning more or less and by how much? It's unlikely that both impellers if damaged were damaged equally.

Yes, both engines are running in the high 7k. I want to say 78-790]

 

[swatski]

@John Mcpartland I haven't seen anyone ask or you say but what kind of rpm's are you turning?

Is one motor turning more or less and by how much? It's unlikely that both impellers if damaged were damaged equally.

At 7,900 it would be hitting rev limiter, consistent with cavitation (OD gap too large or sealant missing etc.), correct?
(or impeller pitch is off)

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[Williamsone46]

Yes, both engines are running in the high 7k. I want to say 78-790]

Yeah sounds like a cavitation issue, I would say you wouldn't want them turning more than 7600 rpm at wot.

 

[Liveto99]

On the first picture on this whole thread there looks like a little nut like I had in mine is there on the top right. That is what caused mine to run at 27. Brown nut not one that goes on a bolt.

 

[Liveto99]

Here

 

[swatski]

View attachment 76980 Here

Good eye! Others have noticed that too - and it could be an issue, looks like a piece of wood/bark - that can easily cause a lot of havoc; however, the OP reports issues with both pumps and they are not new so likely something else is not quite right with the setup.

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[John Mcpartland]

Good eye! Others have noticed that too - and it could be an issue, looks like a piece of wood/bark - that can easily cause a lot of havoc; however, the OP reports issues with both pumps and they are not new so likely something else is not quite right with the setup.

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That is no longer there
I think it was a piece of a leaf or something that was floating in the make when we pulled out.

 

[John Mcpartland]

Ordered the new impellers today, hopefully they be here soon

 

[John Mcpartland]

The impellers look perfect, but .015 mm would be hard to see

 

[Julian]

Those impellers look really good. Where were the spark plugs last changed?

 

[John Mcpartland]

Those impellers look really good. Where were the spark plugs last changed?

6 weeks ago