Unexpected impeller malfunction

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Re: Unexpected impeller malfunction

Postby Shuggy » Tue Jul 07, 2015 10:32 pm

True Blue, True Blue?

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Re: Unexpected impeller malfunction

Postby Nick » Wed Jul 29, 2015 4:57 pm

sahona wrote: I've got memories of an SS headless screw across the bore in an impellor with no other metal visible in the hub (but it might have been encapsulated in the rubber). This lay in a slot in the shaft and transmitted power to the impellor. I guess yours possibly wasn't stainless, in my case the screw was still there but the impellor hub was all gronched up. Johnson pump?

Same deal - no other metal visible in the hub.

I think the pin was ss as the sheared off stub looked shiny. Volvo engine.

Still can't understand how the pin could have escaped - there was no possible route.
- Nick 8)


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Re: Unexpected impeller malfunction

Postby DaveS » Thu Jul 30, 2015 5:09 pm

This is not directly relevant to the described incident, but I have experienced glue failure leaving the rubber impeller stationary while the metal ring with the screwed pin in it rotates futilely.

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Re: Unexpected impeller malfunction

Postby Bodach na mara » Mon Dec 14, 2015 11:26 am

You aint seen cockpit chaos until you have seen my extended family (all 7 of us) in the cockpit of Wight Dawn.

Meanwhile, to return to the boring subject of the impeller, I assume Nick means "shear pin" when he says "spindle" as the spindle is what I would call the shaft, and if that is broke, it is not a five-minute job to fix it. On my engine, the shear pin was a threaded stainless rod that screws through the rubber and hole in the shaft. To remove the impeller is a feckin awful job as you need to remove the shaft first. Well, actually that bit is easy. It is getting the fecker back in that is the problem. I thought on milling a slot in to the hole in the shaft, as replacing the shaft always (a.) b*ggers the seals and (b.) involves removal of the pump to relocate the wee bits that connect the slot in the rear of the shaft to the slot in the camshaft. So last year I replaced the (obsolete) pump with a nice shiny new one from Mack Engineering. Which I hope has a slotted shaft to enable drawing the impeller from the front.

Meanwhile, I have seen a problem like Nick's, but on an outboard. The pump on a Force 3 outboard has a nylon bush inside the rubber which has a longitudinal groove milled down it on each side. These groves slide over the shear pin which is in a hole in the prop shaft and is trapped by the thin bit of nylon and the rubber. Like Nick, I could see no problem with the impeller until I tried to remove it and found it would not come. Not only that but it turned freely on the shaft. Eventually I turned it to the right bit and it slid off to reveal a new annular slot that had been chewed by the shear pin round the nylon. Thus when the shaft went round, the impeller didn't.

PS the sweary word filter changes "beggars" into "annoying people"! Which made one sentence above look very peculiar.

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Re: Unexpected impeller malfunction

Postby sahona » Thu Dec 17, 2015 5:47 pm

While we're on about raw water pumps, it's amazing the things you get up to during idle time when the shed is too cold.
I've just been round the Christmas cards with a micrometer looking for 10thou stock to make gaskets from.
One or two of the charity ones come near - most are too thick. Just thought you'd need to know...
http://trooncruisingclub.org/ 20' - 30' Berths available, Clyde.
Cruising, racing, maintenance facilities. Go take a look, you know you want to.

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