keyway sucked up into motor

dunc333

Seaman
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Dec 27, 2009
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54
has anyone ever heard of the impellor keyway being sucked up into motor before on a yami 70hp 2 stroke enduro.well this has happened keyway found in passage in exaust cover water galleries after motor over heated so we tookcover off found keyway so dropped leg opended pump housing and keyway gone just weird.the boat was travelling at 13 knots and when it let go the motor over revered for a few seconds and we kept driving for about 30 secs till alarm went off any advice from the yammi gurus.we have ordered new pumpkit and willfit when it arrivies any other advice what to or how it happened. my theary is it came out a few hours before and then the pump un seized from shaft,realy just guessing here though kind regards dunc333
 
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99yam40

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I always thought a key fitted into a keyway.

I do not see how a half moon key could slip out of it's slot while the impeller was over it holding it in.

I also do not understand if that actually did happen, how it would cause the motor to over rev
 

dunc333

Seaman
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Dec 27, 2009
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im hearing what you are saying ,I dont believe it either but that is the fact ,the key was gone .i know it surley cant be possible for the woodruff key to come out of shaft with impellor over it but it has or was not put back togeather on last servce ,which was 5 hours running time before and it pumped water fine thats why im asking you gurus if you have ever heard of this happening before because i have not cheers dunc333
 

99yam40

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I have never seen it happen .
Most people complain about not being able to get the key out of the keyway.

I have seen the plastic come loose from an impeller so the rubber would not spin and pump
 

Sea Rider

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Sep 20, 2008
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Real strange issue, was the recovered key from inside powerhead the original SS one ? probably on last service a much smaller key was placed and somehow the drive shaft let go key through impeller vanes and right into into exhaust cover water passages.?

Happy Boating
 

dunc333

Seaman
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Dec 27, 2009
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Searider i think you might be on the right track will size key in shaft and then will measure against new one once it arrives and I will let you know results regards dunc333
 

dunc333

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Dec 27, 2009
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54
i am going to try and get the owner of the motor to post some pictures stay posted guys.
 

DJOZ

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Jan 26, 2018
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Hello everyone, Dunc 333 has me to post some pics and give an overview and background of what happened. 1999 Yamaha CV75, (75A in the USA I believe) I've had since new. Yearly service by Yamaha reps in Sydney and flushed after use for 5 - 10 minutes. Usually within an hour after use. A couple of minutes at idle then 3000rpm then back to idle and unplug fuel line until fuel runs out.
Generally running for 2 - 3 hrs on Sydney Harbour at least once a month. I drift fish so motor is stopping and starting maybe 20 times a trip.
Occasional outside trips which usually involve trolling at 5-7 knots for several hours at 1500>2000 rpm.
Boat was serviced in July 2017. Invoice states pump parts, spark plugs, gear plug washers and 2 throttle washers that were sticking.
Fished at the end of July and boat did not go back in the water until mid October for various reasons. Boat was trailered 150km each way to Shoalhaven Heads. Unfortunately I encountered a sand bank on this trip but boat ran well after this with no issues.
Next trip was January 2018 when the incident happened. Boat was checked and prepped the day before. Both son and I commented on the strength of the tell tale and how easily the motor started.
Was the tell tale working at the ramp? I can't say for sure. (My bad).
15 to 20 minute run at 3500rpm then down to 2500rpm for 15 knot zone for maybe 5 minutes. Coming out of the zone we sped up to 3500rpm and the motor over revved. I thought we may have hit some weird cavitation or worse - dropped a blade or even the whole prop.
Pulled back the throttle and went to go again and motor over revved and heat alarm went off.
Shut down and checked for blockages or line tangles with nothing obvious.
Went to try again and alarm was still there and noticed no tell tale. Called a mate and got towed back in.
Back home tried a few things then pulled the exhaust covers off. Son found a piece of metal. There was also some salt build up with bits of grit in some areas and the area where we found the key had rust stains around it........

A few days later his mate who is a marine mechanic came around to have a look and I showed him the bit of metal.
"Woodruff key - there's your problem". Pointed to where we'd found it which he thought was most unusual and he seemed to think we'd find another key. Took bottom of leg off but could not find another key. He thought the key was slightly worn but still serviceable. Impeller looked like new but the white plastic housing was slightly distorted and discoloured which he attributed to the heat. Put the old key back in and away she went! Ordered new parts.
I'm slightly mechanical having worked on surface mount robots for 26 years but I'm no marine guru. BUT - I can't see how that key got there.
Her's the pics where you can see the rust stains showing where we found the key.
I'm waiting for the parts and we'll reassemble. Having cleaned the covers some of the interior paint has been abraded away - does anyone think this will be a problem?
Cheers DJOZ
 

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99yam40

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I do not think the key could just come out and get into the water stream.

I have no idea how the impeller could turn that long with out a key to hold it to the shaft.

all you can do is replace the housing and water pump kit and then see if all is well
 

Sea Rider

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Sep 20, 2008
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You can flush an OB all day long after use in salt water, but due to constant ON/OFF, heat/cold cycles will inevitably collect salt layers and crusts,which will need to be removed mechanically to immaculate clean condition as factory delivered for OB to cool fast and efficiently. Expect to find this cond inside powerhead, exhaust covers and cylinder head water passages on OB's that are conveniently flushed till fuel runs out and OB dies, worse if not flushed at all after use.

Click image for larger version  Name:	Salt Crusts.jpg Views:	1 Size:	140.6 KB ID:	10532399

Whatever was painted when assembled will peel off, don't worry about the powerhead interior, get same color touch up paint for the exterior. Now you know that damaged water pump keys must not be used..

Happy Boating
 

DJOZ

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Cylinder head was replaced about January 2017 due to pin holing, scale build up and corrosion causing overheating, so yep, salt eventually gets in there.
Apart from that the motor has been virtually trouble free which is not too bad for 18 yrs old.
Some more pics. The rust stains make me think that that particular key had been in situ for some time. So either it was:
1. operating without a key
2. operating with another key that came loose when we picked up the revs
3. operating with that key which came loose and caused rust stains within an hour.

There may be another scenario but I can't think of it at the moment because I'm going to the cinema with the better half in an hour and have to flush the brain of all things maritime and angling related.
"I Tonya" I believe so I'm going from salt to skate.
Connecting muffs now for brain flush. In this instance one uses electricity rather than fresh water. Switching on power.
PHHHTTTTZZZZZZ. All done.
Thanks for the input.
Cheers DJOZ
 

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99yam40

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want to explain how the key coming out of the water pump impeller could in any way cause the RPM to jump up?
not much power is used to pump water.


need to inspect the drive shaft splines into crank,lower unit insides, prop hub, or prop if that happens
 

mphelle8vld

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Aug 17, 2005
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321
I would guess the tech pushed the impeller onto the shaft without the keyways aligned, pushing the key out of it's slot and down into the output chamber, eventually carried up into powerhead. The impeller must have been a tight fit, working until you ingested some sand from that bar causing the impeller to begin to spin on the shaft which you can see from the photos. The motor eventually got hot enough, ran lean and over-revved. Did you notice any scuffing in the ring area of the pistons? Might be worth a compression check while you wait for parts.
 

DJOZ

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99Yam -All inspected and all good. No obvious wear at all. Facets straight and square. I'm guessing the impeller creates more "drag" than what we may think when locked to the shaft. If that was the cause.?????

mphell - boat ran OK offshore for around 5 hours after the sandbar incident and another 6 hours fishing in the river two days later so bu%^ered if I know. It's all very odd. Turned the motor over with the exhaust cover off after we found the key and the pistons look like new - didn't dismantle to rings. Good idea though - I will have compression test done when we reassemble.

Sea rider - the key was definitely not SS so I'll be interested to see if the replacement is and also interesting that my son's mate thought we'd find another one which ties in with your idea. Or a combination of a few things. It's a weird one.

BTW - "I Tonya" was full so we saw "The Florida Project" Don't bother. It's craptacular. Even the wife said so.
Cheers DJOZ
 
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99yam40

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All inspected and all good. No obvious wear at all. Facets straight and square. I'm guessing the impeller creates more "drag" than what we may think when locked to the shaft.
Cheers DJOZ

nope, water pump does not load up the motor.

and I see no way motor running lean could cause that much power to make the prop spin up like that to over rev
 

mphelle8vld

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nope, water pump does not load up the motor.

and I see no way motor running lean could cause that much power to make the prop spin up like that to over rev

Not trying to convince anyone, just a guess on my part. I've heard plenty of stories over the years of two strokes "racing" just before they seize. The only evidence I have is from enduro kart racing when I was much younger, You could hold a gloved hand in front of the cooling fins of the single cylinder motor giving a surprising boost of power for passing (for a few seconds), any longer would toast the piston.

"Put the old key back in and away she went!"... If you hadn't said this, I would have suggested a spun prop, as in damaged the rubber hub on the sandbar and then finally letting go.
 
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99yam40

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a little bit of common sense.
a small rubber impeller pushing a small amount of water will not load up a motor that is built to power a prop to push a boat
 

dunc333

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Dec 27, 2009
Messages
54
ok so no load on impellor ,he will have to check prop bush then .i know they did not water test when they put old keyway in also dont know if they put in gear on muffs ,so gearbox oil; should be checked for water ingress and metal filings .maybe they copped a plastic bag around prop ?? there will be a outcome sooner or later cheers dunc333
 
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