Changing A Raw Water Impeller (How To) - Page 3 - SailNet Community

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  #21  
Old 07-28-2008
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On my Yanmar 2QM15 engine, you have to pull the entire water pump assembly off to get to the cover of the impeller. This also means loosening the drive belt. When I had the engine survey done, the seasoned mechanic told me to buy an extra water pump assembly and a few rebuild kits. His thinking was that it was easier and quicker to just replace the entire pump assembly if the impeller failed, especially if you were underway, needed the engine, and were not in calm sea conditions. He told me to try and imagine having to rebuild the pump in 10 to 15 foot seas when the engine might be needed, and boat handling might require you to be available elsewhere. He said that to pull the broken pump assembly and install the new one could be done in under 10 minutes, but sitting at the table, rebuilding one, would take much longer, especially in rough weather and under stress, especially if the engine was really needed at that time. He suggested rebuilding the broken one later, when time, sea conditions, etc. were more favorable. Something worth considering, since you can't always predict when the impeller will go bad, and chances are it is when you really want to have the engine working.
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Old 07-28-2008
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Originally Posted by LittleWingCA View Post
Something worth considering, since you can't always predict when the impeller will go bad, and chances are it is when you really want to have the engine working.
As I stated in my article if you replace your impeller annually, and don't run it with limited flow or dry, you should almost never have an impeller failure.

I have been replacing impellers annually and this is the first cracked blade I've had in 12 years and it was because I let it run knowingly with limited flow.

In twelve years of annual impeller replacements not once have I needed to change an impeller at sea or mid season due to failure. This is the first one and I killed it knowingly..

I would have never needed to replace this one if I didn't have a baby with a sleep schedule on board (actually, it's our sleep schedule and if she gets off hers I don't get any) and I had stopped for 5 minutes to clean the sea strainer.

Spare pump is a good idea. I carry one, yet to use it, and a re-build kit..
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Last edited by Maine Sail; 07-28-2008 at 11:11 PM.
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Old 07-29-2008
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I saw recently something referred to as a quick change impellor cover. Didn't take a lot of interest in it as our Bukh is a easy as can be to change. Yanmars can be a bugger so I wondered if these things were of any use.

As per usual thanks to H for original post. I'm a believer in his principle of change once a year whether needed or not. After the first and only time I had an impeller fail and I didn't have a spare I've changed religiously every year and only bother I've had was from a bloody plastic bag.

Also do the same with belts. It's not a huge expense and the peace of mind makes it all worthwhile. (and you end up with lots of spare belts and impellers, lots and lots.)
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Old 07-29-2008
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Fuzzy...I think you are referring to speedseal.com
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Greetings,well this JH4 has had a cooling prob since it's refit in Cartegena,lucky me,4th mechanic to get involved, figure out why no flow out the Exhaust.
short version,replumbed bad strainer routing,all the way back to the pump and disected pump to find the Backing plate missing! Probably in the deep bilge with
many other parts,tools and sunglasses. this isn't a common replacement part.
Got it shipped in and now it flows like mad and runs very cool.too bad it smokes blue,overheated too many times... Lesson, Assume nothing! Cheers
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Quote:
Originally Posted by halekai36 View Post
As I stated in my article if you replace your impeller annually, and don't run it with limited flow or dry, you should almost never have an impeller failure.

I have been replacing impellers annually and this is the first cracked blade I've had in 12 years and it was because I let it run knowingly with limited flow.
I still find this disturbing, Hal. I can't find your comments on the incident atm, but, IIRC, you let it run with mildly restricted flow for a short while. ISTM an impeller designed for this application should be able to tolerate that. What brand was the failing impeller?

I know you have had poor results with Globe's blue "run-dry" impellers, and I have found others who have experienced similar failures: Where the hub breaks free of the surrounding material, so the vanes no longer turn. But I notice that some Globe impellers appear to have non-metalic hubs and some metal. One of the failed ones about which I read was reported to have a "plastic" hub. I wonder which yours was and, if it was non-metalic, if the Globe impellers with metal hubs are better?

Did you try to contact Globe about this early failure? I certainly would have. Tho I note that, in a couple of the articles I found, it was reported Globe was unresponsive to complaints about this product. I find that disquieting.

Jim
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Just to add a few more tips.

Don't be a silicone junkie. If you clean off the old gasket as recommended you shouldn't need a sealer.

An old product called "Gasket Cinch" will keep the gasket attached to the cover while you are trying to get it on. Gasket cinch is aplied like contact cement, coat the cover(always attach the gasket to the removable part) and the side of the gasket that attaches to it and allow to dry and then using a couple of screws to aling the gasket just press. Gasket cinch is a low stick kinna stuff and will allow the gasket to be removed later with little effort.

Now you have the plate with the gasket attached just reach for your tub of BTG (Boat Trailer Grease). Go ahead, get a little on your finger and rub on the side of the gasket that goes to the housing.

BEWARE of rubbing grease on the housing as it might have a sharp edge.

As most mechanics know--If you put the first bolt in at the 12 o'clock position the cover will almost swing into place. Remember to always start all bolts before tightening any and then in a criscross pattern.

The next time you have to change the impeller the gasket will come off with the cover and be easy to remove and clean up will be a snap.

If that day comes when you have to change the thing in a hurry just pull the cover change the impeller and use the old gasket and you should be done in about 5 min.

If of course you have one that is easy to get to

Rick
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I still find this disturbing, Hal. I can't find your comments on the incident atm, but, IIRC, you let it run with mildly restricted flow for a short while. ISTM an impeller designed for this application should be able to tolerate that. What brand was the failing impeller?

I know you have had poor results with Globe's blue "run-dry" impellers, and I have found others who have experienced similar failures: Where the hub breaks free of the surrounding material, so the vanes no longer turn. But I notice that some Globe impellers appear to have non-metalic hubs and some metal. One of the failed ones about which I read was reported to have a "plastic" hub. I wonder which yours was and, if it was non-metalic, if the Globe impellers with metal hubs are better?

Did you try to contact Globe about this early failure? I certainly would have. Tho I note that, in a couple of the articles I found, it was reported Globe was unresponsive to complaints about this product. I find that disquieting.

Jim
I got nowhere with Globe and if I remember correctly it was a metal hub.

My current thinking is that my Johnson impeller was an old one when I installed it. My baot came with two new spares but who knows how "old" they were. Johnson has since changed the rubber compound to a product called MC97 which is supposed to be better.

Limited flow can be enough to heat up the impeller but still enough to not over heat for a while. I have actually measured my raw water pump before (not on this boat) with my infrared under a "partial flow" and it was over 200 degrees..

The only lubrication is water and you have rubber on bronze spinning at a high rate of speed. Lose flow and you have less lubrication and cooling.

I've had this happen before and never seen cracks so my only guess is that the impeller was many years old and the rubber was aging before I actually installed it? That is my best guess because my engine had only climbed to about 190 and I was still getting a "mist" out my exhaust. If you've experienced a partial blockage you'll know what I mean by mist..

After this incident I bought 3 new impellers all with the new MC97 compound and threw away my one year old used ones. At $16.00 for an impeller why risk it..
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Quote:
Originally Posted by halekai36 View Post
I got nowhere with Globe...
Yours would be the third incident I've read of where somebody had premature failure of a Globe RunDry [tm] impeller and got no satisfaction from Globe Composite Solutions, Ltd. That's enough for me. Any company can have product failures, but I expect vendors and manufacturers to stand by their products.

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...and if I remember correctly it was a metal hub.
So much for that theory

Quote:
Originally Posted by halekai36 View Post
My current thinking is that my Johnson impeller was an old one when I installed it. My baot came with two new spares but who knows how "old" they were.
...
I've had this happen before and never seen cracks so my only guess is that the impeller was many years old and the rubber was aging before I actually installed it?
That would certainly explain it!

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Originally Posted by halekai36 View Post
After this incident I bought 3 new impellers all with the new MC97 compound and threw away my one year old used ones. At $16.00 for an impeller why risk it..
Indeed! I'll buy two and install one this season. Next season I'll install the other and order a new spare. Each season: Wash, rinse, repeat.

How can you tell if Johnson impellers are fabricated with their new MC97 compound?

Jim
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How can you tell if Johnson impellers are fabricated with their new MC97 compound?

Jim
Like this..

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