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Old 28-02-2014, 12:35   #1
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Perkins 4108 raw water pump.

Hello all, any help would be appreciated: I ran the Perkins 4.108 in my Seamaster 27 with the raw water inlet closed, for about 3 minutes. When I realised this, I stopped the engine, then opened the valve and ran the engine for about 1 minute, looked for water coming from the exhaust - none. Presumably I have shredded the impeller. I've ordered a new impeller etc. My ask is: Any advice on fitting would be appreciated, and: when the new impeller is fitted, do I need to prime the pump, or just start up?
Thanks and regards,
Harry Bond.
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Old 28-02-2014, 12:55   #2
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Re: Perkins 4108 raw water pump.

Be sure to retrieve all the pieces of the impeller. If you dont find them in the pump you will have to track them down investigating further down the line... maybe in the Trans cooler if it has one. Note the rotation of the impeller when you open the cover and rotate the new one as you install so the blades are bent the same way. Most installs are low enough to not need a prime.
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Old 28-02-2014, 12:57   #3
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Re: Perkins 4108 raw water pump.

How difficult or easy depends on access to the pump.

First thing.
The impeller is likely wrecked. The bad news, you may now have bits of impeller throughout the cooling system, and really need to make sure that all the bits are removed.
The impeller sits on a spline. The old impeller can normally be prised off carefully (be careful not to damage the pump casing. Access to the impeller is a matter of removing the front cover plate of the pump

The new impeller is then pushed onto the spline
Trick, use a cable tie to hold down the vanes of the new impeller to help get it started into the pump body, removing the tie once you get the impeller started on the spline, and use plenty silicone grease as well
If access is difficult, it can be easier to remove the pump from the engine.
Think your pump is this one

Jabsco 3270-200 - " bronze pump, 40-size, flange-mounted with BSP threaded ports / Bronze Engine Cooling Pumps / Pumps / Marine / Xylem JabscoShop - Jabsco & Rule Pumps and more - from the experts

But main thing is to make sure all the old bits are removed.
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Old 01-03-2014, 06:00   #4
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Re: Perkins 4108 raw water pump.

All of the above is good advice, especially the cable tie hint! I would add some glycerin type impeller lubricant prior to starting the pump. To look for the other pieces from the impeller, you will need to remove the black rubber cap on the end of the heat exchanger. Usually the pieces end up there. Depending on how your hot water heater is installed you may need to shut off the valves to the hot water heater first (note how many turns so you can put them back at the same level). Will probably spill some when you disconnect the rubber cap so have some rags ready and a bucket if you actually have to disconnect any hoses.
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Old 01-03-2014, 06:31   #5
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Re: Perkins 4108 raw water pump.

Dish soap works well as impeller lube and you probably already have some, or you can make a special trip, waste 4 hours and 6 dollars.
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Old 01-03-2014, 07:47   #6
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Re: Perkins 4108 raw water pump.

Agreed, dish detergent will work just as well. The last two impellers I bought came with the lube.
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Old 01-03-2014, 08:02   #7
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Re: Perkins 4108 raw water pump.

A couple of ideas on how not to have a repeat performance in the future
1) Hang your engine ignition keys on the cooling water intake valve, that will remind you to open the valve when you need to start the engine. Put the keys back on the valve handle when you have finished with the engine and closed the intake valve

2) Consider purchasing a "speed seal" Welcome to Speedseal Safety Covers
Impellers have been tested running dry for up to 5 minutes, and the design make's removing and fitting the cover plate a lot easier
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Old 01-03-2014, 18:19   #8
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Re: Perkins 4108 raw water pump.

Quote:
Originally Posted by KDH View Post
All of the above is good advice, especially the cable tie hint! I would add some glycerin type impeller lubricant prior to starting the pump. To look for the other pieces from the impeller, you will need to remove the black rubber cap on the end of the heat exchanger. Usually the pieces end up there. Depending on how your hot water heater is installed you may need to shut off the valves to the hot water heater first (note how many turns so you can put them back at the same level). Will probably spill some when you disconnect the rubber cap so have some rags ready and a bucket if you actually have to disconnect any hoses.
Thanks to everyone for the advice.
The hot water tank is not connected. How to remove the rubber cap? Can anyone recommend a book on diesel engine maintenance/simple repairs (nothing too complicated - just to keep things running smoothly).
Thanks again.
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Old 01-03-2014, 19:14   #9
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Re: Perkins 4108 raw water pump.

I will admit I've done this too. Except it ran for 30 minutes (at least) before it started overheating. Was very surprised.

Rubber cap is just a hose with a hose clamp if I remember correctly. So loosen clamp, warm up with a hair dryer, remove gently.
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Old 02-03-2014, 05:14   #10
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Re: Perkins 4108 raw water pump.

On our heat exchanger the rubber cap looks more like a defined cap with an outlet. However, he is correct that you should just be able to remove the hose clamp. We just pulled ours off no heating required.
Nigel Calder's book Marine Diesel Engines and Repair http://www.amazon.co.uk/s/ref=nb_sb_...er%2Caps%2C507
Also available at Abe Books(UK) online. Calder also has a larger volume, which includes the same info (although I like the illustrations in the stand alone book better) called Boatowner's Mechanical and Electrical guide. If you do not have any experience in boat electrical systems I recommend you get that one instead.
Also, if you go to the engine library link on this forum you should be able to download the engine workshop manual for the 4.108. Just noticed today that you are in Wexford. My boat is currently in Crosshaven!
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Old 02-03-2014, 05:39   #11
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Re: Perkins 4108 raw water pump.

Quote:
Originally Posted by KDH View Post
Also, if you go to the engine library link on this forum you should be able to download the engine workshop manual for the 4.108. Just noticed today that you are in Wexford. My boat is currently in Crosshaven!

Thread drift, but I hope you got to try the fish and chips at the Cronin pub
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Old 02-03-2014, 06:27   #12
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Re: Perkins 4108 raw water pump.

I was always reluctant to change that impeller on my 4-108 since if the water flow was good then why mess with it. However many years ago, I decided to be more pro active and change the thing. No problem and I carefully lubed it prior to start up with some sort of lub that seemed correct. Within several hours of operation, the flow out the exhaust was inadequate and some of the vanes on that new impeller had broken. I attribuated it to the lub that I had used and now I always use the dish detergent rather than any pretroleium based product.

It should not be necessary to prime the pump as long as the intake is well below the waterline and the impeller does not need to overcome much vertical height.

Whenever I bleed the engine, I never shut the water intake as many do since I always think that harm could be done to that impeller. However be very aware that extended cranking that engine could result in water entering the cylinders which is the reason many will shut off the water intake to preclude that from happening.
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