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Old 13-12-2010, 17:55   #16
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Originally Posted by hughfree
Yanmar 3YM30 water pump">Raw Water Pump Failure
I purchased my 3YM30 in 2005 in Florida. Since that time I have gone through 3 raw water pumps. The pumps are built of low quality metals and the first thing that happens is the pump shaft rusts and causes the seal to leak. Then salt water sprays all over everything and the pump bearings rust away rapidly. The pulleys all rust and cause the alternator and pump belts to chew up. My solution is in progress. I have custom made new pump shafts in 316 stainless and am buying stainless bearings, etc for the pump internals. The boat is now in Fiji. Anyone else have problems with these pumps? Anyone have any suggestions?
According to the manual the pump does have a two bearing system. If the material of the shaft is magnetic then that maybe the whole problem. Once the seal starts to leak then there goes the bearings.
Other then that, being over worked is the only other thing I could see (w/o actually seeing one personally) that could cause failures.

I have a 3JH4E and I'm going to be checking the shaft the next time I'm at the boat. Fortunately it is gear driven, no belt tension to worry about.


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Old 13-12-2010, 18:12   #17
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I think the corrosion could have something to do with a spray of salt water onto a hot engine.
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Old 13-12-2010, 18:16   #18
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We have been through two of these pumps since 2005. The first was replaced under warranty. Every Yanmar dealer I have spoken to says these pumps used to be very robust, but they are now pretty worthless.

On the first pump, we initially had the seals re-built - that lasted about 2 weeks.

Now we always carry a spare.
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Old 13-12-2010, 18:18   #19
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I see this all to often (as in the OP).

The bottom line is that components on engines usually but not always give us some sign of impending problems.

If a water pump leak is causing rust......it has been in failure mode for a while. I wouldn't blame the pump.

I have seen fronts of engines that are a mass of rust.....rest of engine clean......This is operator lack of vigilance....Rust doesn't spring up over night.

I have notified customers of my observations and they say
"they'llgetaroundtuit....they never do.....I'll wire brush the engine and paint it.........anyway.

Once again....the common way that pumps/alternators fail is due to belts being too tight and the side load on the shafts.
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Old 28-11-2011, 21:06   #20
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Re: Yanmar 3YM30 Raw Water Pump Failure

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Originally Posted by Chief Engineer View Post
I see this all to often (as in the OP).

The bottom line is that components on engines usually but not always give us some sign of impending problems.

If a water pump leak is causing rust......it has been in failure mode for a while. I wouldn't blame the pump.

I have seen fronts of engines that are a mass of rust.....rest of engine clean......This is operator lack of vigilance....Rust doesn't spring up over night.

I have notified customers of my observations and they say
"they'llgetaroundtuit....they never do.....I'll wire brush the engine and paint it.........anyway.

Once again....the common way that pumps/alternators fail is due to belts being too tight and the side load on the shafts.
Don't know if this thread is too old, but how tight should a v-belt be? I'm guessing you press your finger in the midpoint and look for a deflection of some fraction of an inch?

I've got the service manual but there is no description of proper belt tension for the raw water pump. But it does say for the alternator belt: 6 to 8mm deflection when new, then remeasure after 5 minutes of running the engine for 8 to 10mm of deflection.

I don't know that we'd use the same because both the belts and distances are different.
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Old 28-11-2011, 21:23   #21
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Re: Yanmar 3YM30 Raw Water Pump Failure

No thread is too old if it's informative!

It all comes down to how much wrap there is on the sheave. The more wrap around the sheave the less tension one needs for grip. If too much tension with a lot of wrap it will get hot from the belt having to bend/squeeze around the sheave under tension, eventually breaking down the belt.

The length of the belt does not make any difference. If it's so long that it shakes, it should have an idler pulley to maintain stability. There's also different styles of belts that can be adapted to overcome problems.

One has to go by the manufacturers recommendations or do the R & D yourself.
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Old 23-05-2012, 14:39   #22
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Re: Yanmar 3YM30 Raw Water Pump Failure

Any issues with coolant pump(not raw water) ?/
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Old 23-05-2012, 15:44   #23
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Re: Yanmar 3YM30 Raw Water Pump Failure

Nope. Not so far. I've replaced one, but the engine had 2500 hours on it, so not a shock.
My oversize alternator required a TIGHT belt, which undoubtedly hastened the failure. I've installed Balmar regulators which ramp up the start charge, so I don't have to tighten as much.

BTW, regarding the raw water pumps.

A new M19 belt from Yanmar is TOO TIGHT even at loosest setting when new.

I've just burned through two of the stock pumps again (I've got two engines), so I said the heck with all that and plumbed in two ELECTRIC pumps which are relay controlled by the oil pressure switch.

They work ok, but will steam at high RPM after a while.

But they sure as heck DON'T LEAK!!!
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Old 20-04-2015, 07:16   #24
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Re: Yanmar 3YM30 Raw Water Pump Failure

What electric pump are you using? What oil pressure switch? I'm in the process of doing the same conversion. Thanks Mike
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Old 20-04-2015, 08:20   #25
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Re: Yanmar 3YM30 Raw Water Pump Failure

I'm away from the boat for a few days, but I'll give you the pump details when I get back home.

The oil pressure switch is on the left side of the engine near the filter. I ran it to a relay that enables the pump.
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Old 01-01-2017, 15:17   #26
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Re: Yanmar 3YM30 Raw Water Pump Failure

At about 650 hours my 2008 Yanmar 3YM30 raw water pump started to fail. I noticed it leaking a tiny bit of water but ran engine a few more outings while keeping an eye on it. Last week I had enough and removed the pump along with its mounting bracket so I can better clean up the small amount of corrosion the leaking caused and of course get a new pump. Funny thing is that for the last year or so I have thought the belt driving the pump was too loose. But it pumped water perfectly and appeared to be adjusted out as far as possible so I lived with it. Maybe the looseness gave me a bit more time? And after reading this thread I might be getting two pumps.
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Old 01-01-2017, 15:39   #27
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Re: Yanmar 3YM30 Raw Water Pump Failure

Fix your pump, and buy a spare. I wouldn't buy two.
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Old 01-01-2017, 15:57   #28
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Re: Yanmar 3YM30 Raw Water Pump Failure

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Originally Posted by a64pilot View Post
Fix your pump, and buy a spare. I wouldn't buy two.
How easy is it to fix? I supposed I need to take it apart to see what's what. I have the parts catalog so maybe I just need to dig into it (like most things on a boat)? I am guessing that the pump wasn't too far gone but it was clearly leaking.
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Old 01-01-2017, 16:59   #29
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Re: Yanmar 3YM30 Raw Water Pump Failure

Usually just seals, but maybe bearings too.
Not real hard
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