Perkins 4108 - replacement sea water pump

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neil1967

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My 1987 Perkins 4108 has a Johnson raw water pump fitted, which has seen better days, and I am planning to replace it. It would appear that 4108s were fitted with either Johnson pumps or Jabsco pumps. In my limited experience it appears that Jabsco pumps are more common and therefore it will be easier to get spares for them (?) Would the Jabsco pump be a straight swap for the Johnson, or is it more complicated than that? I presume that in either case I will have to realign the adaptor plate?

Any thoughts much appreciated.

Neil
 
Having had a 4108 for years, and having changed it 4 years ago, as far as I can recall the drive for the pump is at the front of the engine. If that is the case mine certainly was jabsco. There are several different models of the 4107 and 8, some were "lowline engines" and others had "stuff in different places" and some were indirect whilst mine was direct.
Why they fitted Johnson and Jabsco is a mystery.
Local chandlers eher seem to sell spares for both models mainly the impellors.
Why specifically do you want to change??
 
I'm planning on a liveaboard life starting in 4-5 years time and hopefully lasting 15-20 years so I am keen to have a reliable engine that I can maintain. The existing pump needs replacement and the choice is to replace like for like or to replace the johnson with a jabsco. I think that it will be easier to get spares for a jabsco and possibly they are better known so if I have to seek help in remote places perhaps it will be easier - or perhaps I am wrong?

Neil
 
I replaced my Jabsco with a Johnson so I went the other way.

The bolt holes were in exactly the same place and I didn't need to realign the adaptor plate at all. My pump is mounted on the front of the engine on the timing chain cover and driven off the end of the camshaft. The only time you should need to realign the drive is if the timing cover is moved. Perkins manual quotes a special tool.

I bolted the new pump on to the cover but only just nipped up the bolts slightly beyond finger tight. Turned over the engine a few times and checked if the pump moved ( it didn't ) Then I tweaked the bolts a fraction more and ran the engine for about 3 minutes. Stopped and snugged the bolts down.

Engine has done about 300 hours since the replacement with no problem.

I went to the Johnson because a new pump off the shelf was about 2/3 the price of a Jabsco and the impellers I found were about 3/4 the price of the Jabscos.

I don't throw perfectly good impellers away. I keep a couple of spares and inspect the one in the engine every season ( 50 - 100 hours of running? ) Since i replaced the pump 300 hours ago I am still on impeller 1. ( I do have a raw water flow alarm though )
 
Last edited:
neil1967 said:
I'm planning on a liveaboard life starting in 4-5 years time and hopefully lasting 15-20 years so I am keen to have a reliable engine that I can maintain. The existing pump needs replacement and the choice is to replace like for like or to replace the johnson with a jabsco. I think that it will be easier to get spares for a jabsco and possibly they are better known so if I have to seek help in remote places perhaps it will be easier - or perhaps I am wrong?

Neil
Click to expand...

I believe that Johnson have gone down market, it's a fact that I will never buy one of their pumps again having had to have it replaced FIVE times (under guarantee thank goodness) in the last 2 years. In addition about 18 months ago I replaced a Jabsco impeller with a Johnson equivalent and that impeller packed in 2 months ago. I've actually re-fitted the old Jabsco one and hoping to pick up a new Jabsco replacement this weekend.

Johnson are not doing themselves any favours at all by allowing manufacturing standards to to go into free fall. I just hope that Jabsco don't follow them. :(
 
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