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Old 17-03-2016, 22:15   #1
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Repeated failure water pump Yanmar 3ym20

I repowered with a new yanmar 3ym20. It now has 1000 hours and looks like a piece of junk because the water pump has failed 3 times spraying salt water everywhere. It goes through belts like crazy. I am at my wits end! Had a 50 mile passage yesterday off Colombia, checked belts before I left, had to motor for 4 hours, now the engine is covered in belt dust, the belts are practically falling off and the water pump is leaking again! Sure would like to fix this so it lasts. Appreciate all suggestions.
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Old 17-03-2016, 23:05   #2
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Re: Repeated failure water pump Yanmar 3ym20

You using yanmar belts? I was, and had the same issue. Switched to auto parts store belt and zero dust now.
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Old 17-03-2016, 23:39   #3
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Re: Repeated failure water pump Yanmar 3ym20

Could be the belt is too tight, or belt is trying to provide too much horsepower. If the pump is leaking, bearing is probably worn. Early bearing wear is usually caused by too tight belt.
Are you running a stock alternator? Is it continuously outputting high amps?
There are products to stop belt slip.
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Old 18-03-2016, 00:39   #4
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Re: Repeated failure water pump Yanmar 3ym20

It does sound like the belts may be too tight, but take a straight edge and see if the pulleys are aligned.
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Old 18-03-2016, 00:56   #5
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Re: Repeated failure water pump Yanmar 3ym20

If it's a Johnston impeller pump it has a small lip seal inside which seals the shaft, it might need changing. For the slight cost of two new sealed bearings from a bearing supplier you might as well change them whilst you have the pump off.


The pully on those pumps is just locked onto the shaft with a grub screw and is easy to get misaligned, the straight edge check is a good idea, otherwise just eyeball it, the human eye is pretty good at spotting misalignment.


These things require very little torque to rotate so the belt does not need to be very tight, just firm is usually sufficient.


I needed to replace the pump on my 3GM30 years ago and found that the Yanmar spare was $850. I bought the same pump with a pedestal mounting, made a mounting bracket from alloy angle and got away with it for less than $300.
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Old 18-03-2016, 01:24   #6
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Re: Repeated failure water pump Yanmar 3ym20

Some info which may or may not be helpful:

I found the Yanmar OEM belt for my 2GM pump was too loose, causing slippage and belt dust. I went down 1cm in length with a good belt and have no such problems.

These pumps are easy to rebuild for well under $100. Buy generic seals and bearings for a fraction of the Yanmar price. Replace the impeller and cover gasket, clean up the shaft with fine abrasive paper (especially where the lip seals go), and it will be as good as new.

And as already mentioned, check pulley alignment.

Good luck!

Graeme
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Old 18-03-2016, 06:15   #7
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Re: Repeated failure water pump Yanmar 3ym20

Quote:
Originally Posted by donradcliffe View Post
It does sound like the belts may be too tight, but take a straight edge and see if the pulleys are aligned.
Indeed.

See ➥ Belt & Pulley - Cruisers & Sailing Photo Gallery

And ➥ Belt & Pulley - Cruisers & Sailing Photo Gallery
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Old 18-03-2016, 09:53   #8
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Re: Repeated failure water pump Yanmar 3ym20

Belt's way too tight!
You can run it quite a bit looser than specified as the wrap on the pulley is what provides the drive. That little water pump requires VERY little power so the belt dust is probably because the pulley is out of alignment, a result of the bearings having failed. (my Yanmar belt is coming up on 1100 hours, and is still in good shape).
My maintenance schedule is to a) replace the impeller every second year. Johnson Pumps have impellers that substitute for the "proprietary" Yanmar. (eg: the 3GM30F uses Johnson's 09-810B-1 kit for their F4 series. I buy for about $35.
b) Replace bearing and seal every four years. Most industrial type suppliers have the exact same bearings, and stainless steel seals; my total cost $28 this year.
Take a look at the pump cover plate, if it has significant wear, at such low hours as yours, it is due to the bearings running out of true, due to that excessive belt tension. May have to replace, or make, a new one.
Take care to deflect the impeller blades in the correct direction as you assemble the pump and lube with generous coating of non-petroleum oil.
Make sure the sea cock is open before firing it up and you should enjoy the next 2 years of trouble free use.
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Old 18-03-2016, 17:48   #9
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Re: Repeated failure water pump Yanmar 3ym20

You have already received some very sound advice, but here is a bit more:
You stated that the water pump failed three times--three new pumps or the original one was rebuilt and failed three times? If it is the old pump then you are obviously doing something wrong, such as driving the bearings on the shaft with a hammer, wrong bearings, wrong seals or both, or you have warped the pump housing.

Confirm that the drive pulley on the crankshaft and the driven pulley on the water pump are in perfect alignment using a straight-edge.

Switch to a name brand (Gates, NAPA, etc) V-belt--a toothed (dentura in Spanish) belt rather than a common V-belt. The toothed belts grip far better with much less tension. Tension the new toothed belt only so tight that you cannot make the pump pulley slip with your hand grip. Re-tighten after a couple of running hours. Your alternator bearings will thank you for this!

Good luck!
Harry
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Old 18-03-2016, 20:06   #10
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Re: Repeated failure water pump Yanmar 3ym20

Hi there I have had repeated same problem to. A good way to fix any scores under the lip lip is to get it metal sprayed at an engineering shop. Regards to belt dust you may have paint lifted from the sides of the pulley making a rough surface gradually wearing the sides down. Another good idea is to have a complete internal assembly made so you can replace easily, I think pump vender in the US can supply complete shaft bearings etc. Good luck.
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Old 24-03-2016, 21:24   #11
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Re: Repeated failure water pump Yanmar 3ym20

My 3ym30 salt water pump failed at 250 hrs, belt wasn't tight.

Had to replace the bearings as the seal had gone, was an easy job for the local marine mechanic, didn't cost much.

Have you replaced the pump? The belt issues could also be due to a mismatched pulley.
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