Replacing the Salt Water Impellor on a Cummins engine

According to the experts on www.boatdiesel.com  one of the recurring problems on Cummins Diesels is the raw water pump. It is a Sherwood 17000 model.  I carry a complete spare pump assembly, as well as several spare impellors.

The impellor is a serviceable item. The Cummins manual specifies to remove it and inspect every 300 hrs / 12 months.

I’d recommend removing the rear plate and visually inspecting the impellor for missing / cracked blades on their schedule (and whenever you accidentally run the engine with the seacock closed) and replacing it every 2 or 3 years. Unfortunately removing and replacing one of these is a bear of a job.

The Pump

This is the raw water pump, located on the port side of the engine. 

The Impellor

This is the spare impellor from my Cummins spare parts kit. Note the date code: May 2003. Impellors ‘age’ even when stored properly, losing flexibility. I chose to install a newer one than this.

The impellor spare parts kit contains:

·         Impellor

·         O ring gasket for the pump body / rear plate seal

·         Woodruff Key – the oblong steel key for the drive shaft

·         Rubber disc to cover the rear plate end of the drive shaft

 Contents of the impellor kit, and my impellor extractor.

Keep the old woodruff key as a spare (it doesn’t really wear out)

There are 2 variations on these impellors. The type dictates the method used for extracting it from the pump.

1.   Some impellors have a threaded end on the center shaft. If you screw a large (3/4” I think) bolt into this thread you can pull the impellor out using that bolt. These do not use a rubber disc on the end – the thread keeps the woodruff key in place. The original one on my engine had this type.

2.   Other impellors have no thread on the end, and use a rubber disc to hold the key in place (and not score the end plate). The replacement shown above is this type. Mine was this type so I needed to use an impeller puller shown in the picture shown above to get mine out.

 Replacing the Impellor

1.  Close the engine seacock. Don’t forget to open it afterwards, otherwise this might all be for naught……I hate when that happens.

2.  Remove the 3 ½” bolts holding the backplate. Note which way the impellor rotates (CCW -counter-clockwise): I painted an arrow on the outside of my backplate to remind me. Incidentally, the manual says to remove the water hoses too – this is not necessary.

3.   Remove the old impellor. Ha - simple words, but possibly a struggle the first time, unless you’ve lived right, or someone greased the old impellor properly…

a.   If  you have the threaded version, and a suitable bolt handy, try screwing that on the impellor.

b.   The manual shows 2 methods, using either 2 screwdrivers or 2 needle-nosed pliers. Good luck with them – it’s impossible to develop enough leverage to drag the little devil out (and the screwdriver method risks scoring the pump body).

c.   I bought an ‘Impellor Extractor’: Jabsco/Rule part #50070-0200 (West Marine page 240 part #286880) $77.99.   Seadog also make one – it needs to be sized for a 3 ¼” impellor.

4.   If the impellor failed, find all the bits! There were 12 blades, so try to get all of them. If not, make a mental note to remove and flush the aftercooler, transmission oil cooler and heat exchanger until you find all of them.

5.   Remove and save the old drive key (and the O ring too).

6.   Insert the new impellor. More simple words – this is the worst step.

a.    Use 1 or 2 wire-ties to compress the impellor vanes (the correct way remember CCW rotation…) then use Pam spray or grease or liquid soap as a lubricant to help shove that puppy back in there. Be liberal with the lubricant and the swear-words here. As you push the impellor in, the wire-tie slides off.

b.   When the impellor is half- to three-quarter in, try to rotate it to line-up the keyway. Insert the new woodruff key all the way in.

c.   To get the last inch or so inserted, bolt the backplate on, and evenly tighten the bolts. You may need longer bolts….

7.   As the manuals say: “Re-assembly is the reverse of dis-assembly – except you say ‘Bugger’ in different places”.  Don’t forget to install the new O ring, with a little grease.

8.   Oh yeah – open the seacock, and test…..

Other Hints

 Impellors can be ordered from:

·    Cummins dealers – probably the most expensive

·    West Marine 17000K page 237 part#4572731 $66.00

·    South Bay Marine   www.sbmar.com  They are a Cummins dealer in Southern California, run by Tony Athens, who is the resident Cummins Guru at www.boatdiesel.com  He has produced a much improved Impellor for these pumps, and I’m happy with the one I’ve installed. I think it was around $75. 

Keep several spares onboard, and keep them out of the sun and the engine room (the UV and heat will degrade them quicker). Try to use newer ones (less than 1 or 2 years old). This all applies to generator impellors too…

I bought and installed a ‘Speedseal’ cover plate for my pump from the UK . Basically, it’s a replacement plate held on by knurled thumbscrews instead of bolts. The idea is to reduce the time to replace an impellor at sea. While it does work as designed, the time saving is trivial, as the time to remove/replace the cover plate is minimal compared to actually extracting/replacing the impellor…..

If you’ve never replaced an impellor before, you should know how: they will fail, and at the most inopportune time. Try to replace the generator impellor first for practice: it’s the same principle, but much easier as it is a fraction of the size.

Jeremy Bell. AT34 #48 “Tardis”