Impeller housing smashed apart plus grove in prop shaft just below spline

Jon7

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Feb 9, 2013
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I had some issues with my 2002 mercury 3.3 hp 2 stroke with water pumping but after a simple impeller change I thought it was sorted, it stopped pumping water again and when I opened lu the impeller housing had blown apart, the shaft just below the spline the connects to the engine was groved deep as well and seemed to have gotten very hot as the metal had changed colour. The impeller itself was in fine condition not a problem but the housing above it smashed. I took it to an outboard guy who had not seen the impeller housing smashed before (just my luck) and thought it could be oil seals gone bad and caused the grove, I decided to chance it and try it with new impeller housing on ran it briefly and the water came through tell tale again, put into gear the (engine was running erratic not catching revs very well at all) water stopped coming out tell tale again shortly after and when took off lu the prop shaft had completely sheared off at the groove point, so engine is now in for strip down new seals gaskets the works prop shaft etc, seems too big a job for me to tackle myself and have left it with the outboard guy who knows his stuff. I was just wondering has anybody seen or heard of such problems before? Seems to be a rare one as there a metal surround on the inside where impeller goes? How worried should I be? It just seemed odd the impeller housing was smashed and what would cause the grove? Would the oil seal actually cause that? Any input welcomed, cheers Jon
 

Grub54891

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Re: Impeller housing smashed apart plus grove in prop shaft just below spline

Guessing the l unit has bad bearings or something. Thus locking up and breaking the shaft?
 

Jon7

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Re: Impeller housing smashed apart plus grove in prop shaft just below spline

Shaft broke because it had a deep Grove worn in it at the top end near where the spline goes to the motor itself, but the concern is why it has worn in, like would the oil seal get hot enough to score the prop shaft all the way around, weakening it so as soon as it was put in gear it was too much and completely broke/ sheared off. It was also odd because of the impeller housing breaking apart like it had been smashed not melted. The prop shaft was all nice and tight on the bottom end where it goes to propeller no play at all it all seemed good and tight so it just didn't seem to add up how the impeller housing could be broken like that it's a real worry because if there is no known cause how can I stop it happening again, lower unit all in normal working order seems problem up top somewhere as that's where the grove was and the break
 

Laddies

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Re: Impeller housing smashed apart plus grove in prop shaft just below spline

Not being able to see much from here, it's real had to tell the cause. How ever I would speculate that the problem you are having presently was caused by the simple impeller change being done improperly.
 

Jon7

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Re: Impeller housing smashed apart plus grove in prop shaft just below spline

That's the thing impeller wasn't even damaged, it was changed by the outboard guy as I haven't worked with outboards before and didn't realise how simple it was so took it to an outboard specialist/shop. The impeller remains undamaged. Which would suggest the impeller housing was smashed from the outside not from within. It had no chance of sucking anything up either as was running in a tub. Would the top part what ever caused the shaft to gouge somehow of thrown a piece of whatever it is down smashing impeller housing? What would cause the grove up top of the shaft? I cannot imagine a top oil seal being able to cause that damage to the shaft as I understand they are rubber and would of thought the rubber would melt not the metal gouge. It was a colour that looked like extreme heat had been on it (yellowed,bluey,purple mix) so I was just wondering if anyone else had similar problem with top end of the shaft? The outboard guy was Speculating that oil seal has broken down up top causing the shaft to scour a deep gouge in it and eventually snap shaft. The broken housing is strange as all impeller etc in tact nothing wrong with it at all, it's the housing which was broken. I just cannot understand how rubber would cause a deep grove all around the shaft like that and concerned it's something worse? I would have thought this has happened so someone else before which is what I was trying to establish really if anyone knows of this problem?
 

Grub54891

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Re: Impeller housing smashed apart plus grove in prop shaft just below spline

A seal will make a groove in a shaft over time. Creating the weak spot,then you bump a submerged log or something and snap it goes.or just cracks and breaks later.as far as the dis coloring on the splines area, it was probbally heat treated from factory and that's all normal. Can't tell ya about the smashed housing,never had that happen. How about some good pictures of it?
 

Grub54891

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Re: Impeller housing smashed apart plus grove in prop shaft just below spline

Yeah fuzzy pic,defiantly broke! Maybe somehow take a better pic,also of the upper spline pieces.
 

Jon7

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Re: Impeller housing smashed apart plus grove in prop shaft just below spline

The motor is not here with me so unable to take some more photos. I guess the seal must have worn the shaft then from what you have said and maybe the impeller housing got hot from the heat ddown the shaft or something, I just can not think of another way the housin would just break like that? It will probably remain a mistery because how it broke like that is strange as I cannot see where it would happen. I guess no one else heard if this before either?
 
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