Yanmar 3GM30f raw water pump

[carlager]

I have have unmounted the water pump">raw water pump (type Johnson Pump F4B-903) on our Yanmar 3GM30f.

I can see a black O- ring on the shaft in the weephole (re. the attached photo).

Does anybody know if this O- ring is placed right ?




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[Sailor Bob 350]

Raw water pumps don't rely on O-rings to keep water in, they use pressure bearings. Rubber O-rings would be ruined by the friction.

Raw water pumps are designed to drip if the bearing is going bad, so you will notice there is a problem before a catastrophic failure occurs. Having the pump seize or worse while offshore is a really bad day! So if there is a drip, you have to replace the bearing or replace the pump. I've never replaced a bearing, but I gather it requires special equipment.

Fortunately, there are people who rebuild pumps and resell them, for about half the price of a new pump.

My boat is 8 years old, and I've had to replace the pump 4 times! 2 lasted for several years, 2 lasted for less than a year (one when it was new!). But the pump on my Universal M35B is notorious for this.

I now carry a rebuilt spare so I'm not missing sailing time finding a replacement. On a cruise of any length, I'd consider a spare pump essential.

[DougR]

Yes, the O ring is correctly positioned. The purpose of this O ring is as follows:

If the water seal on the pump gets worn or damaged and leaks water, the water will move along the rotating shaft until it reaches the O ring. The larger diameter of the O ring will act like a slinger and cause the water to drip or even get thrown from the shaft at the position of the ring, which is at the drip opening.

Without the O ring, the water could continue to move along the shaft until it contacted the back side of the oil seal where it might work its way under the oil seal and into the bearings and perhaps ultimately into the crankcase.(in the cease of a gear driven pump)

If you rebuild the pump, be sure to place the replacement O ring at the drip holes.

DougR

[bobnlesley]

Yes, the O ring is correctly positioned

Sorry, but I disagree:

We had a bad summer for water-pump problems/failures and as a result I pulled apart three separate 3GM30F water pumps - two were the post 1996 European models and one was the pre-96 European/Rest of the world model.

On all three pumps, one of which was virtually new and so I know for a fact that that one had never been disassembled/wrongly rebuilt previously, the small O-ring was located immediately behind the lipped-seal which faces into the rear of the impeller chamber and immediately ahead of the hard plastic spacer with the three prong-legs. I don't now how to add photos, but if you pm me an email address, I know I have some of one of the disassembled pumps somewhere that I could send you.

I've no idea what it actually does there, I just put them back together in the same order that they came apart.

If you need a new pump, the post-96 European model pump is about half the price of the other one and they're directly interchangeable, the only difference seems to be the way in which the impellers are locked onto the shaft, so the impellers themselves can't be interchanged..

[carlager]

Originally Posted by bobnlesley

Yes, the O ring is correctly positioned

Sorry, but I disagree:

We had a bad summer for water-pump problems/failures and as a result I pulled apart three separate 3GM30F water pumps - two were the post 1996 European models and one was the pre-96 European/Rest of the world model.

On all three pumps, one of which was virtually new and so I know for a fact that that one had never been disassembled/wrongly rebuilt previously, the small O-ring was located immediately behind the lipped-seal which faces into the rear of the impeller chamber and immediately ahead of the hard plastic spacer with the three prong-legs. I don't now how to add photos, but if you pm me an email address, I know I have some of one of the disassembled pumps somewhere that I could send you.

I've no idea what it actually does there, I just put them back together in the same order that they came apart.

If you need a new pump, the post-96 European model pump is about half the price of the other one and they're directly interchangeable, the only difference seems to be the way in which the impellers are locked onto the shaft, so the impellers themselves can't be interchanged..

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[carlager]

Thanx a lot for your very informative answers. Bob I would very much like to se your photos. However I can't find your mail addres. Mine is capcon(at)mail.dk.


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[deblen]

Doug R is correct. The o-ring on shaft is a water slinger.

But I learned another "trick" when googling the above.
You can use another o-ring in place of the seal "garter springs",if you are having problems with seals leaking too often.-according to this link.
Changing the Raw Water Pump Seals on the MD2030 | Engines | How To Articles | Manta Owners Association

No experience doing this-just an FYI / Len

[DotDun]

Yes, it's positioned correctly. As already stated, the o-ring acts as a slinger to protect the bearings from salt water if/when the lip seal fails. Where it's at on the shaft doesn't matter.

[tdh1849]

Suggestion, look up the tel# for, " Complete Yacht Service" Yanmar dealer in Ft.Lauderdale, ask for the owner Mark ( USMC) and tell him I told U to call, I'm Pat N. from there now living in Tampa.
He is good, knows everything there is to know about Yanmar3gm30s.

[bobnlesley]

Originally Posted by carlager

Thanx a lot for your very informative answers. Bob I would very much like to se your photos. However I can't find your mail addres. Mine is capcon(at)mail.dk.


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Emailed you the photos along with a list of part numbers for the bearings/seals which we used to rebuild our pump; they cost less than 1/10th of the price of the 'official' Yanmar/Johnson 're-build kit'.

[DotDun]

If you need to talk to someone, call Depco Pump, they are experts in all pumps.

Depco Pump Company

[bobnlesley]

You can use another o-ring in place of the seal "garter springs",if you are having problems with seals leaking too often.

Persistent seal failure is often due to the shaft being 'worn' at the point where the seal-lip sits on it, so another 'trick' is to replace the 'standard' single-lipped seal with a double lipped one, which provides two lines of seal, but more importantly, locates them on an unworn portion of the shaft.

I've been told (never tried) that you can achieve the same result by using a standard single-lipped seal, put don't press it fully into the recess in the pump body, if it sits back 1.5mm - 1/16", it causes no problem to the bearings, spacers, etc. ahead of it and similarly seats the seal on a different and unworn portion of shaft

[RaymondR]

I agree with the water slinger hypothesis.

Years ago I went to buy a new genuine Yanmar spare water pump for my 3GM30 and was quoted around $800 for pump and mounting bracket. I recoiled in horror, bought the same size Johnston pump with a pedestal mounting for less than $300 and knocked up a mounting bracket from a piece of alloy angle I scrounged from a scrap metal bin. I have an enjoyable little gloat every time the incident comes to mind.