Premature impeller failure cause - SailNet Community

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  #1  
Old 07-09-2012
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Premature impeller failure cause

I repowered my Cape Dory MS 300 back in the winter of 2008-2009. At the end of the first season going from a Westerbeke 46 to a Westerbeke 55. Had an impeller failure at the end of the summer in 2009. The blades of the failed impeller were fine, but the brass fitting/bushing and key pin had delaminated from the rubber bushing. This happend with about 100 hours on the engine.

Last week upon starting the engine I noticed that the burbs of water from the exhaust were much less frequent than normal (15 to 30 sec intervals vs the normal 5 to 8 sec). Turned out that the impeller agained failed in the same manner. It was probably still spinning somewhat providing a little water to the pump and exhaust.

The first impeller was branded as a Westerbeke, the second as a Johnson. Don't know if they are made by the same manufacturer or not. Any thoughts on what the cause may be? My mechanic thinks it could be that the thru-hull and seacock fitting might be undersized for the new engine. I think the thru hull is 3/4" with a 5/8" hose fitting. I looked through the engine manual and installation guide and didn't see a a minimum size for the thru hull. I'm going to call Westerbeke and or Hansen Marine (the Westerbeke dealer) also to see what they think.

Sort of an aside, but I was surprised that the impeller for the new 55 hp engine was much smaller than the one on the old 46 hp. Any ideas will be appreciated.
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Old 07-09-2012
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Re: Premature impeller failure cause

Could there be something blocking the sea-water flow to the impeller? Running the impeller dry could cause the premature impellor failure.
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Re: Premature impeller failure cause

I believe Westerbeke uses Johnson Pumps. "Johnnyquest" is correct something is interrupting the raw water flow or there's not enough. Call Joe Joyce at the Westerbeke plant...phone 508 823 7677 ext.234 and explain your problem ( Joe is the service mgr.). That 55 pump should do the job.
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Re: Premature impeller failure cause

If it's similar to my 27, I would also take a look at the cover plate. The cover plates get grooved over time reducing the suction and also need replacing. Don't know if it would cause the level of problem you had, but worth checking. I replaced a grooved cover 2 years ago and get better flow.
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Old 07-09-2012
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Re: Premature impeller failure cause

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Originally Posted by Tempest View Post
If it's similar to my 27, I would also take a look at the cover plate. The cover plates get grooved over time reducing the suction and also need replacing. ....
After 100 hours??? I have a thousand or so more than that on my 2 yanmar pumps (catamaran) with no failures
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Re: Premature impeller failure cause

Pull off the cover plate and open the thull. You should get a good shot of water coming out of it. If you are not getting a lot of water out, you have an issue leading to it.

Typically in impeller failures, I see the bladdes get hot and fracture off - not the brass seperating. However, I have only seen two failures. Others may have seen this separation.

When I replace the impeller on my boat (which I religously do every 12 mos or 100 hrs), I put on the imeller with a lot of dish soap. THen I replace the cover and leave it loose. I open the Thull until water flows freely out of it, then tighten with the thull open to inure it is wet and well lubricated. I understand that you can burn up a impeller very quickly (60 seconds or so) if not well lubricated. That could cause premature failure.

Again, my first check would be to loosen the cover and open the thull and make sure water is gushing out. Good starting point.

Brian
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Re: Premature impeller failure cause

Quote:
Originally Posted by TropicCat View Post
After 100 hours??? I have a thousand or so more than that on my 2 yanmar pumps (catamaran) with no failures
You're right, of course, I missed the 100 hr, new engine part.
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Re: Premature impeller failure cause

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Originally Posted by Cruisingdad View Post
Pull off the cover plate and open the thull. You should get a good shot of water coming out of it. If you are not getting a lot of water out, you have an issue leading to it.

Typically in impeller failures, I see the bladdes get hot and fracture off - not the brass seperating. However, I have only seen two failures. Others may have seen this separation.

When I replace the impeller on my boat (which I religously do every 12 mos or 100 hrs), I put on the imeller with a lot of dish soap. THen I replace the cover and leave it loose. I open the Thull until water flows freely out of it, then tighten with the thull open to inure it is wet and well lubricated. I understand that you can burn up a impeller very quickly (60 seconds or so) if not well lubricated. That could cause premature failure.

Again, my first check would be to loosen the cover and open the thull and make sure water is gushing out. Good starting point.

Brian

I checked the strainer and pulled the hose off the thru hull. Got a gusher when I opened the sea **** so I think the water flow is good but maybe it's not good enough. Kind of like sucking through a thin straw vs a wider one?
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Re: Premature impeller failure cause

Quote:
Originally Posted by LinekinBayCD View Post
I checked the strainer and pulled the hose off the thru hull. Got a gusher when I opened the sea **** so I think the water flow is good but maybe it's not good enough. Kind of like sucking through a thin straw vs a wider one?
I am beginning to suspect a product failure if you have followed the installation steps I discussed. Replace the impeller with Westerbeke parts. All I use are Yanmar direct parts - no aftermarket. Replace every 12 mos or 100 hours.

Replace your impeller as I described. Give her a good run for some hours. Open is and take a look at the impeller. Also, at 55ish HP, you should put out about 5 gallons of water/minute from the exhaust. Stick a bucket under there and see what you get. THat is what the specs are for Yanmar anyways, IIRC. CHeck out the amount with Westerbeke.

Hope these suggestions help. ALso, make sure your hose is not collapsing under higher rpms (from Thull/strainer to block).

Brian
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Re: Premature impeller failure cause

Quote:
Originally Posted by Cruisingdad View Post
I am beginning to suspect a product failure if you have followed the installation steps I discussed. Replace the impeller with Westerbeke parts. All I use are Yanmar direct parts - no aftermarket. Replace every 12 mos or 100 hours.

Replace your impeller as I described. Give her a good run for some hours. Open is and take a look at the impeller. Also, at 55ish HP, you should put out about 5 gallons of water/minute from the exhaust. Stick a bucket under there and see what you get. THat is what the specs are for Yanmar anyways, IIRC. CHeck out the amount with Westerbeke.

Hope these suggestions help. ALso, make sure your hose is not collapsing under higher rpms (from Thull/strainer to block).

Brian
Called Hansen Marine (where I got the engine) this morning. They were saying the thru hull should be 1". I think I have a 3/4" with a smaller hose fitting attached. (being 450 mi from the boat I cant check right now) I'm goung to check with Westerbeke directly also. Can't find a specification in the installation guide or manual.

Thanks for the help. The Hansen guy thinks that the impeller is having to work too hard to get water causing the delamination.
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