Missing Impeller Lobes.....

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ash
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Missing Impeller Lobes.....

Postby ash » Mon Apr 13, 2009 9:13 pm

....Do you go looking for them?

When winterising the Beta BZ482 in November, I noticed that water was running back out of the raw water pump. I took this as a sign that the impeller was damaged.

Checked this weekend and found one of the lobes torn off. The engine has only done 77 hrs since new, but the impelller was left in the previous winter with a 50% antifreeze mixture. I hadn't noticed a reduction in water flow, but then it pumps a lot in comparison to the MD6A.

My engine has the raw water pump at the front and then has a pipe up and over to the heat exchanger. I removed the outlet from the pump and the outlet from the heat exchanger. Crew held a bucket under the pipe whilst I directed a mains pressure hose into the heat exchanger oulet. One bucketful - nothing but halfway through the second bucket the bit of lobe appeared.

I was pleased to find that my pump has an 'O' ring instead of a joint so that makes life easier. The shaft has a slot it is easy to get a grip of the hub with needle nosed pliers and pull it out.

Ash
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sahona
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Re: Missing Impeller Lobes.....

Postby sahona » Tue Apr 14, 2009 10:29 am

I wouldn't look for them (haven't lost any yet), but it does throw another angle to the order in which the cooling water meets the various components. (TOP
http://www.ybw.com/forums/showflat.php? ... ost2260197)
You have just convinced me that the gearbox should come immediately after the pump (mine has a large sump with a fair bit of unmoveable gunge in there already!) .
That way, hopefully, none would get into the exchanger tubes.
Coincidentally, this is one of the current tasks in progress.
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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claymore
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Re: Missing Impeller Lobes.....

Postby claymore » Wed Apr 22, 2009 3:48 pm

Ash - I hate you. If that had been me the thing would not have been found until someone passing shouted to me that clouds of smoke appear to be coming from the exhaust. Parahandy would then make me feel rather stupid by encouraging me to demonstrate my inadequacies as a mechanic and it would end up costing me a fortune in beer and Old Pulteney as the auld gizzard drank the locker dry, a smug smile (rather an unpleasant smugness) playing over his withered features as he scoffed at the contents of my tool box and marvelled at his own ability to change an impeller using a plastic coat hanger.
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Re: Missing Impeller Lobes.....

Postby FullCircle » Wed Apr 22, 2009 9:39 pm

claymore wrote:Ash - I hate you. If that had been me the thing would not have been found until someone passing shouted to me that clouds of smoke appear to be coming from the exhaust. Parahandy would then make me feel rather stupid at his own ability to change an impeller using a plastic coat hanger.


Dear Claymore, you were obviously not placed in this life to be an engineer, but to hold a more measured and ethereal position, where mere mortals would struggle for air.

Parahandy, after all, as the below decks engineer for the Vital Spark, so would only be demonstrating that for which he born.

I should be glad that, with no more than a frown, I could induce friends to fettle my fine craft for no more than a dram. Seems fair cheap to me.

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ash
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Re: Missing Impeller Lobes.....

Postby ash » Mon Apr 12, 2010 9:58 pm

Before starting the engine, I opened up the pump to fit a new impeller for the new season.

My intention was that I would have an old impeller which would be used only to pump the antifreeze mixture at the end of the season and would sit in the mixture through out the winter, and the 'working' impeller wouldn't be subjected to antifreeze.

Found that I was again missing a lobe! Grrrr. This impeller had only done one season - 30 hours - hadn't been run dry - hadn't been subjected to antifreeze. The remaining lobes didn't show any signs of cracking. The lobe which had been bent all winter was OK.

Managed to back flush the missing lobe out in less than half a bucket.

I wonder if I am causing damage when I start to draw up the antifreeze mixture? I don't think so - it would only be a fraction of second without water flow. At the end of this season, I'll have a look in the pump before I start the winterising. The other point is that I don't have a water filter so I might be dragging something through the pump and so damaging the lobe but I don't think that it's very likely.

At this speed, I think that I should have a filter after the pump to catch the broken bits!

BTW, I can confirm that the lubrication gel that is supplied with the impeller is water based. I only used half the sachet last year, and being scottish, I taped up the sachet and kept it as backup. My engine bits are kept in a small toolbox, and when I opened this up, I found a puddle of water and an empty sachet!

Moan over.

Ash
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Nick
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Winterising schminterising

Postby Nick » Mon Apr 12, 2010 10:31 pm

.
We didn't winterise this year - boat sat on the mooring all Winter and started first turn of the key - but I did put a new impellor in first.
- Nick 8)

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ash
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Re: Winterising schminterising

Postby ash » Mon Apr 12, 2010 11:21 pm

Nick wrote:.
We didn't winterise this year - boat sat on the mooring all Winter

From a freezing point of view - you have the advantage of salt water in the raw water side - but even then you might have had a problem with the prolonged sub zero temps that we had this year.

I take it that you had no missing lobes.

Ash
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Nick
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Re: Winterising schminterising

Postby Nick » Mon Apr 12, 2010 11:27 pm

ash wrote:
I take it that you had no missing lobes.

Ash


No, just the usual post-Winter frontal damage :mrgreen:
- Nick 8)

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