Water pump insufficiency 3YM30

[farmer.leo]

If a pump wont prime, there is an airleak in the suction side. Thats it, full stop!

(Not a Vetus pump)

Just tried a brand new impeller and brand new pump cover today. The O-ring looks fine. Still no suction, water will pass if poured via a funnel into the hose so there is no down stream blockage. But it can't suck from a bucket right next to the engine. The hose is fine.

Looks like it is the seal or bearing on the engine side of the pump. Going back tomorrow to take it off the engine, want to look at the manual pictures first.

By the way, it's not the cam - it looks fine and the impeller blades are very much bent when passing over it.

 

[Bosun Higgs]

Would vaseline around the O-Ring a good idea?

Yes. You need to eliminate possible causes one by one. Try using dick tape round any pipe joins, the pump face plate and see it that makes a difference indicating an air leak. Joints that is between pump and inlet.

However I'm pretty sure your problem is pump wear. I had a similar difficulty on a 2gm which ultimately meant that I had to prime the filter every time I started the engine up. The wear was between the back face of the pump and the front face ie the impellor was no longer thick enough. When primed it would work and continue working.

 

[Halo]

Hi Leo
Will be very interested to hear the outcome of your investigations.
I had a similar problem on a 3YM30 and coated the impeller in neat washing up liquid to act as a sealant and lubricant and then revved the engine. This then primed the pump and it has worked OK since. I think I had been nervous of revving until thenand it needed more than tick over to fill the system
Martin

 

[Blueboatman]

Just a thought,
(Blurb bit: Whilst I have the older 3GM and have just fitted new seal/bearings etc for n'umpence. I note that there has always been evidence of scratching on the inside face of the cover, yet it self bleeds very easily. And I run the pulley belt absurdly slack, yet as soon as you try to manually rotate the pump pulley, the pulley belt grips, so loose is good we are all agreed.)

Here's the rub:
I have a galley seawater tap teed from off of the engine water feed just upstream of the engine waterpump. It is then fed through a manual footpump ( and at sink level there is a shuttable faucet too, presumably to prevent air being drawn in, should the seal in the footpump fail)....
Now, I wonder if the act of pumping seawater into the sink, and the then existing "head' of water in the tee upstream of the engine pump..is enough to ensure self priming and continued reliable priming for those suffering the 3YM weakness? The galley pump can certainly draw any air lock out of the system when servicing the impeller.
As I say just a thought that has occurred to me today.

 

[KAM]

Just had a look at the cover plate on my 200 hour 3YM30. It's fairly worn. Two things are noticable. The wear adjacent to the cam is significantly deeper as would be expected from the impeller deflecting. Secondly round the circumference there are patterns of corrosion which appear to be an imprint of the impeller vanes during lay up periods. (always well flushed with corrosion inhibitor but impeller left in position) I would have expected the wearing surface to be polished even if worn. Both these observations lead me to suspect the cover and possibly whole pump body are poor quality material. The impeller itself is in good condition. My previous boat used under the same conditions had a volvo with jabsco pump. I never had a problem in 25 years. There was never any significant wear on the cover or body even though it ran dry a few times. Only had to change the bearings and seals once. I will get the cover resurfaced but this should not be necessary at 200 hours. Does anyone know if there is a difference the materials used in these pumps brass vs bronze etc. Has anyone thought of having the wearing surfaces chrome plated.

 

[vyv_cox]

The cover of my 3GM30F is brass and had suffered dezincification. I believe it to be a Johnson pump. It is easy to resurface it yourself, abrade using papers on a piece of glass as a flat base. This is not an expensive item, chromium plating it would probably cost more than a new brass one. On some models, without stamped numbers on the outer face, the plate can be reversed.

 

[brianhumber]

These rubber vane pumps, like all good designs are simple and thus normally very reliable. They are widely used in industry as well as lesuire applications.

My filter is some four five foot above water line and then leads to the pump but this arrangement does not give any trouble and allows quick removal of weed etc without mucking about with seacocks. The pump reprimes happily without needing to add priming water into the filter.

The pump is/has been ultra reliable and I have just replaced the impeller after five years as tiny little cracks were just seen in the rubber at the roots of the vanes. Suggest you check the easy things first such as the plate fit, making sure the joint surfaces are cleaned flat and level to bright brass first. Make a new joint gasket from chart paper every time. When assembling I use washing up liquid to first lubricate the pump if its dry.

The pump has worked happily and primed even with wear of 0.5mm on the cover plate. If you are worried about the wear simply file back to flat surface. I had to do this after about 10 years.

Only time I have has trouble over the 20 odd years with Ronhilda has been after runnng in very heavy silt estuary waters - which ran the seal. This did not stop the pump working, just a fine spray water spun off the shaft.

Changing a seal is very easy takes about an hour if you have a puller and punches, the new seal and bearing required are readily available from internet. Get the GA drawing off the internet from ITT as well to show you where to push pull and tap as required

Brian

 

[KAM]

Good to know that you have confidence in the pump. Just thinking back about estuaries I suppose I did spend some time up some shallow French rivers in the summer with some motoring in and out of very shallow harbours so may have ingested more silt than I imagined.

 

[KAM]

Further to my post on my 200 hour 3YM30 with what appeared to be poor pump performance. I checked out the pump housing today. There appears to be very little wear. Cam dimension is 45.9mm which seems about right from information in other posts. Impeller dimensions and appearance are as new (it's the original one) There appears to be an enormous difference between the condition of the cover plate and the housing. The housing is clean and polished I can still see original machining marks on the aft face. The cover on the other hand is badly worn and pitted with black corrosion. It's almost as if the impeller has bottomed on the shaft without seating on the aft face of the pump but been pressing hard on the cover. It also looks as if the cover material is different (inferior) to have aged so differently to the housing. Fortunatly it's easily cleaned up. Looks as if it would be worth cleaning the face and rotating on an annual basis to even up the wear. Looks like the pump will last a few thousand hours but the wear on the cover is a bit of a mystery!

 

[JimC]

These http://www.kpm-marine.com/rebuildkits.htmldo claim to permanently cure the problem of low suction and poor/non priming.

 

[KAM]

Hi JIMC thanks for the info could not get the link to work had a look at the website but could not find the rebuild kits.

 

[KAM]

OK got it on http://www.kpm-marine.com/rebuildkits.html. Very interesting. Will give them a call.

 

[eagleswing]

OP's question:

The alternator V-belt seemed much thicker and firmer, the raw water v-belt was thinner, perhaps looser. Is there a particular deflection amount these belts should have?

yes, the yanmar service manual has the deflection stated for each kind of belt..someone with access to the manual for your engine could give you the #s


..."That small section of thick black rubber pipe was air tight and visibly looks good...'

i once saw an intake raw water hose failure where the inner lining of the hose had become separated from t he outer shield. under suction, the inner wall collapsed and blocked h 2 9 into the pump. taking off the hose, on inspection it looked great. and blowing thru it or gravity feeding h 2 0 thru it did not cause the wall to collapse..only if the raw water pump was sucking did the inner wall collapse..

moral of this story is, it's cheap insurance to replace the hose too. with properly rated intake water hose...