How long should an impellor last?

actionoptics

actionoptics

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www.actionoptics.co.uk
Had a new BUKH 24 SME fitted June 2006. The impellor ran for 85 hours until removed over winter. Refitted it this year and it ran for another 17 hours before the metal ring parted company from the rubber. ( It happened about 1 mile out of chichester on our way back to the solent in very think fog ) New impellor fitted which lasted 51 hours ( no water coming out of exhaust as we were about to leave St Peter Port for Herm end of July. ) Same fault - metal no longer bonded to ruber. The new engine came complete with new Johnson pump and I have been using genuine Johnson impellors. So, how long should they normally last ? and am I doing something wrong to make them so short lived?
 
No you're not doing anything wrong we've all had it, though traditionally associated with Yanmars. Some people recommend special blue impellers. Some people say they're dreadful. YMMV
 
There seem to be wide variations in life-span. I normally only change mine each spring, doing about 250 hours/year. The only time I had a problem was when the sea-water filter bunged up in less than five hours and it ran a bit dry.

You didn't say if you removed the impeller during the winter, which you should do, along with the fan-belt.
 
I have an old Bukh 24 I change the impellor at least once a year... keeping an eye on the amount of water coming out of the exhaust..
Habit is to fire up and look... you'll soon get a feel for it... Then, if doubtful pull out existing and examine... If at all dodgy replace on spot and buy another spare ASAP
Anyway that's how I work it..
So far have always breezed into Bukh at Poole and bought the things I need..
Oh BTW Al sells Wing screws which make changing impellors a doddle and much cheaper than the "Speedseal" system...( I bought 4 + a spare in case I "bilged" one!)
Another thing I did was get a local guy with a "pierceall" machine to chop a heap of discs out of a brass sheet .... cost minimal... I drilled them on my pillar drill using an old cover as a jig.. The inside of the covers wear and reduce pump efficiency and the outsides are stamped with the makers name etc.. So they can only be used once... But not my discs!! I have at least two on the pump at once so undo wing screwws look at impellor if OK put back and reverse one of the discs ... Hey presto.... Don't forget to change the gasket!!
It works for me any way although the Bukh is circa 83/4..
Now I've written this the thing'll run hot next outing!!
Cheers Bob E...
 
I looked into the question of life six months or so ago and from the Johnson website discovered that there are three kinds of material - one of them is the latest material for all applications. Check you are using the latest type which, according to the manufacturer, is far superior.

Sorry, I don't remember the details and just wrote down the part numbers in my log, for my engines.
 
Impeller blades can disintegrate, but actual decoupling between the core and the rubber structure sounds like our old friend "not fit for purpose" Or pehaps a faulty batch?

I always take my impeller out and keep it in water for the winter. It seems quite capable of doing 2 seasons (300-400 hours total) before precautionary replacement (Volvo MD22 engine) In 10 years I have never lost even a single blade off an impeller, and always install with Vaseline.

PWG
 
er, I wouldn't use vaseline, it's glycerine and you can buy a bottle from the chemists that will last a long time rather than the stuff in scahets from engine manufacturers.
 
Either it is getting to hot due to too little water

Or it is the wrong one i.e too fat

You could try the Nitrile version as this does not expand when in contact with oils.

I tried a Johnson neoprene in a diesel pump and it did not last one tank! The nitrile lasts years.

How are the impellers stored? Are they greased lightly on fitting. The impeller can glue to the metal or generate too much heat around the centre during the system priming.

I have never lost an impeller but replace them yearly.
 
You could use washing up liquid instead of Vaseline, but as you appreciate whatever is used is flushed away in its entirety...the whole point is to prevent distortion or damage when installing, yup, that's the pivotal point...

PWG
 
Ive recently had two early failures (hub de-bonding from the rubber part) with volvo impellers in my Volvo 2003. I suspect batch quality as this never happened me before with the Volvo or the Beta and Yanmar I had in previous boats. I spoke with the Volvo parts supplier who said he had no similar failure reports !!!! He suggested I might not be installing them properly. I doubt that as I've been doing it for years without problem on this and the other engines.
The pump on the Volvo is a Jabsco unit and I've now sourced genuine Jabsco implellers. They are a litle cheaper but much more substantial - the central rubber part of the hub and the vanes are thicker and stronger than the Volvo impellers.
 
Hi
Should be replaced every year full stop. talk to Jabsco. When they come unbonded from the hub usually because they are old.Mayber been in stock long time subject humidity heat and cold. Heating cooling wetting drying all have effect on the compound. You should never dry out and reuse - the blades develop a set and compound contracts therefore pulling away from the 'hub' lots of bull and myths spoken about impellors. Also subject to differing forces when in use plus abrasion plus very differing start up torque especially if not used for a time.
For safety change every time you service and if not used for 2/3 months.
 
Impellers can fail prematurely if the pump housing is assembled with the wrong thickness gasket (or none at all when using gasket goo) as this dimension is critical. If your pump is prone to rapid impeller wear then you can try using 2 gaskets. This will result in a slight reduction in water flow but will increase the life of the impeller if it is failing due to drag against the rear of the pump housing. My current impeller (Jabsco pump) has been in use for over 600 hours, though I normally change every other year after around 200 hours.
 
Thankyou all for your comments/advice. I only bought the new impellors this year from ASAP and they are genuine Johnson parts supplied with a new gasket and a tiny tube of impellor grease. I do have wing nuts securing the plate which make changing the impellor a bit easier.
 
Just read the thread referred to by Racylady and I had not heard about the cable tie trick so I thought it worthwhile repeating it .....I suppose you know the trick of using a plastic cable-tie to hold all the impeller blades compressed until it is nearly fitted home into its housing, then slipping off the cable tie......
 
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