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Old 23-11-2015, 02:35   #1
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Johnson raw water pump. What rpm? (And leaks)

Trying to see why my pump leaks, even though new seals 6 months ago, installed as per spec., shaft looks ok. The lip seals are are press fit into the pump body, the spacer spins freely. Leaks 1 drip per second on the engine, but won't leak on my 'test bench'???

One question is what rpm they run at. I'm using a cordless drill to test it, which goes up to 1400 rpm. Engine is a 40hp Lombardini, max rpm is 3600.

Any obscure reason for these to leak; I do think it is the lip seal, and not, for example, around the seal and where it is seated into the pump housing.


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Old 23-11-2015, 02:58   #2
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Re: Johnson raw water pump. What rpm? (And leaks)

There is probably significant side bearing loads (from the drive belt) when on engine compared to your test bench. Maybe the bearings have some play?
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Old 23-11-2015, 03:27   #3
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Re: Johnson raw water pump. What rpm? (And leaks)

For the pump rpm. Compare pulley diameter to engine pulley diameter. Same size pulley them pump turns at engine rpm. Pump pulley larger then pump turns slower than engine.

Seawater pumps aren't over driven generally so using your drill at max speed should be good to test.
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Old 23-11-2015, 05:18   #4
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Re: Johnson raw water pump. What rpm? (And leaks)

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Originally Posted by daveNZ View Post
Trying to see why my pump leaks, even though new seals 6 months ago, installed as per spec., shaft looks ok. The lip seals are are press fit into the pump body, the spacer spins freely. Leaks 1 drip per second on the engine, but won't leak on my 'test bench'???

One question is what rpm they run at. I'm using a cordless drill to test it, which goes up to 1400 rpm. Engine is a 40hp Lombardini, max rpm is 3600.

Any obscure reason for these to leak; I do think it is the lip seal, and not, for example, around the seal and where it is seated into the pump housing.


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Not enough information. What is the actual model number of the engine?
Is the leak oil or water?

If the pump runs off the cam, it turns at half engine speed. If it is belt driven, you have to figure it out based on engine speed and pulley sizes. If it runs off the idler gear, it most likely runs at engine speed.

If the shaft sealing surfaces are good, the obvious problems would be the seals being installed backwards or being damaged on installation.
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Old 23-11-2015, 05:57   #5
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Re: Johnson raw water pump. What rpm? (And leaks)

Maybe there is corrosion in the exhaust elbow causing excessive flow resistance which is forcing water past the seal.....

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Old 23-11-2015, 09:17   #6
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Re: Johnson raw water pump. What rpm? (And leaks)

Can't answer without knowing the pump model and setup on the engine...cam, gear or belt-driven, for instance? Not to make a pun, but it has a bearing.
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Old 23-11-2015, 11:34   #7
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Johnson raw water pump. What rpm? (And leaks)

Thanks for the prompt replies folks, as usual I gave too little detail!

My pump is F4B-9 10-35098-4 0143. ( not sure what the 0143 means?)

Pump is driven from cam, so max rpm of 1800 seems about right. (Half max engine rpm)

It is water (not oil) leaking, from the shaft and between the seals. There is a tell tale green trail, and I can also see it clearly with my new $10 inspection mirror.

The pump has a shaft drive from the engine so pulley ratios don't apply. Actually you can see the shaft turning and I guess, observe that it doesn't actually turn that fast.

I did recently change the front cover plate and cam. I had previously reversed the cover plate due to to wear, and the front side was even wearing a bit of a groove. The cam looked a bit worn too.

I was about to say that I'm sure the cooling system is not blocked, but that is the one big difference between in-place and bench testing (nothing connected the the pump outlet) so I might manufacture some back- pressure and retest!!


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Old 24-11-2015, 09:45   #8
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Re: Johnson raw water pump. What rpm? (And leaks)

Quote:
Originally Posted by daveNZ View Post
Thanks for the prompt replies folks, as usual I gave too little detail!

My pump is F4B-9 10-35098-4 0143. ( not sure what the 0143 means?)

Pump is driven from cam, so max rpm of 1800 seems about right. (Half max engine rpm)

It is water (not oil) leaking, from the shaft and between the seals. There is a tell tale green trail, and I can also see it clearly with my new $10 inspection mirror.

The pump has a shaft drive from the engine so pulley ratios don't apply. Actually you can see the shaft turning and I guess, observe that it doesn't actually turn that fast.

I did recently change the front cover plate and cam. I had previously reversed the cover plate due to to wear, and the front side was even wearing a bit of a groove. The cam looked a bit worn too.

I was about to say that I'm sure the cooling system is not blocked, but that is the one big difference between in-place and bench testing (nothing connected the the pump outlet) so I might manufacture some back- pressure and retest!!


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Sounds like you need a pump rebuild. Check your oil for "grey milkshake", indicating seeping of water into the sump. If nothing (yet), you still need to check out that cam and the front plate gasket.
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Old 25-11-2015, 13:08   #9
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Re: Johnson raw water pump. What rpm? (And leaks)

Hmm, looks like my issue is not so difficult. I thought I had installed a water seal with a stainless spring (sold as such) but it rusted and with little winter use has created enough probably to be the cause. I also wonder if the new cover plate and cam increased the pressure enough to start the leak!

Does anyone use third party double lip seals?
I have installed one and hoping it works well. It was a much tighter fit and needed some hard tapping with a (I think 18mm) socket to push it in.

Secondly, I assume it does not matter whether the spacer turns freely or not. Mine has worn a small groove due to this rusty water.

Lastly, the very good Compass Marine article states "It is very important that the four little feet on the spacer face the oil seal when reinstalling the seals". However the engineering drawing for mine indicate the opposite (drawing below, part 13). I can't see that it makes any difference which way the feet are facing. The feet ensure there is 'space' so oil or water can get out and drip all over the engine. (Still trying to devise a drip tray!! even a tube and container so I can see leaks without lifting the engine cover!)

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Old 26-11-2015, 16:04   #10
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Re: Johnson raw water pump. What rpm? (And leaks)

The lack of a spring will definitely cause a leak. New cover plate and cam shouldn't cause any leaks unless something else's not up to snuff...

Regarding 'third party' seals, pretty much everyone, OEMs included, use them. Most OEMs (as far as I know, all) buy them outright from seal manufacturers, although certainly there are times when a manufacturer specifies specific characteristics.

That being said, there are differences in quality, and price and country of origin are/is not always an indication of a better seal. Brand name is usually a good starting point if you have no point of reference, but experience is the best guide. I use a local bearing house for every bearing and seal that I can get from them and go by their recommendations if I'm unsure.

A lot of people use an appropriately sized o ring in place of the stainless spring, but I've seen those deteriorate and fail as often as 'stainless' springs...

Regarding the tits on the spacer, I've never seen it make any difference, in several instances have rebuilt pumps and omitted them entirely (sometimes you gotta do the best you can with what you have). I'd think the manufacturer knows more than an article from Compass, but drawings are notoriously inaccurate. I'd put it whichever way you're most comfortable with.
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Old 27-11-2015, 02:28   #11
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Re: Johnson raw water pump. What rpm? (And leaks)

Thanks for that Jim, pretty much confirmed what I thought. I'm confident rebuilding my pump now, but know there will be gotchas and tips that may not be obvious.
Certainly will be checking this thing for leaks very often now, and have all tools to change seals at sea.


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Old 27-11-2015, 02:54   #12
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Re: Johnson raw water pump. What rpm? (And leaks)

Extremely common for that spring to rust and cause a leak.Consider changing it for an O ring.Ask the guys supplying the seals and bearings for appropriate size as they do it often.
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