Cooked impeller

[Twister_Ken]

Motored for three hours with a Bukh 10hp. Then a bit of breeze came up and we managed to sail for 15 minutes or so. When we couldn't make ground over the tide, restarted the engine. Within a few minutes the overheat alarm sounded. After checking the raw water filter (no problem) I changed the impeller, and we were off. The old (less than 12 months old) impeller which is rubber with a metal sleeve that sits on the impeller drive shaft, had broken the bond between metal and rubber, so that the vanes were slipping and either not turning, or doing so slowly. It was also relatively hot.

Local Bukh agent says he has no idea why this should happen. Has the forum?

 

[Strathglass]

Ken there may still be a restriction or blockage in the water intake to the engine. It really depends on the access you have to the various parts. Perhaps something in one of the pipes or the input grating partially shelled over. I have also had problems with broken bits of impeller sticking in pipes and everywhere on a Bukh 36. This took some time to repair.

 

[LadyInBed]

A few years back YANMAR had the same problem. They said it was a bad batch of glue used by a supplier.

 

[Guest]

I also have a Bukh 36 and because access to the stbd side of the engine is restricted it's very difficult to get the impeller in/out. (There is a heat exchanger fitted as well.) Consequently I replace it each year in the apparently vain belief that I won't have to tackle it at sea. Your posting now worries me. Have you found an easy way of extracting the impeller?

 

[chippie]

I had the same problem on an outboard motor with a near new impeller(approx 5 hours). Upon examination I could see that there was a very clean separation between rubber and the steel boss. I sanded the steel and the rubber with 240 grit wet and dry and then epoxied them back together. the impeller is still fine 2 years later. The evinrude agent said it is not an unknown problem.
As the outboard is used primarily for getting a sailing vessel on and off the mooring I saw no need to change the impeller although I always monitor its performance while in use.

 

[Twister_Ken]

To Alan

No problem on the 10hp, its mounted on the front of the engine. Changing is a two minute job, after a bit of practice!

Have you considered whether it's possible to cut some sort of access hatch in the side bulkhead to allow you to get to it quickly, should the need arise?

 

[Chris_Robb]

I know Yanmar has a problem, because my brother went through 3 impelors in as many weeks, that was 3 years ago. Since then he has bought only Jabsco ones, and he has had no more problems.

I change mine on a Perkins 4236 every year - each year they never show any signs of wear, and each time I fit a new one - I keep my fingures crossed for the first couple of hours that its not going to disintegrate as you described!

 

[Twister_Ken]

Not wishing to spread fear and despondency

I should stress that the impeller didn't physically disintegrate, spitting chunks of rubber into nooks and crannies.

in fact, the damn thing looks perfect. Just that when you hold the central sleeve, and twist the vanes, they'll rotate while the sleeve remains still.

Maybe a drop or two of loctite in the right place would restore it to life? OTOH, it's a £10 impeller, vs a £3.500 engine.

 

[Chris_Robb]

Re: Not wishing to spread fear and despondency

Yes - just a quality control issue - but it could be a very dangerous one!

 

[vyv_cox]

Re: Not wishing to spread fear and despondency

I was thinking about this recently. About six months before I replaced my raw-water cooled Bukh with a fresh-water cooled Yanmar, I suffered an impeller failure. The overheat alarm on the engine block sounded, I motored a few metres, anchored and replaced the impeller. When the engine was replaced the water trap was melted internally but intact.

If the same failure occurred on the Yanmar I assume its temperature increase would be far slower. By the time the high-temp alarm sounded, would the trap have melted, filling the boat with exhaust gases? What if it was only a partial impeller failure, could we melt the trap some 10 minutes before the alarm sounded, possibly gassing somebody asleep below? It makes you think!

 

[brian_neale]

Re: Not wishing to spread fear and despondency

I have had an impeller fail on my Yanmar 1GM twice. On neither occasion was there any real damage (as far as I could tell) even though I had to run for a few minutes to get somewhere safe to tie up and change the impeller. Inevitably, it fails just as you are leaving or reaching a mooring/pontoon and not in the middle of clear water.

I have usually changed the impeller each year. These days I tend to change it less often and carry a couple of new ones as spares, plus an old one still in good nick. I check the impeller anyway as part of winter maintenance, and take it out of the pump during the winter to stop the blades taking on a permanent bend. It seems that if they are going to fail, they do so fairly soon after fitting.

 

[LORDNELSON]

I do not know the Bukh 35 but my 3 cylinder Yanmar water pump is difficult to get at (due to inconsiderate
design of the boat structure). It is much simpler in the case of the Yanmar to take the pump off and
then replace the impeller. However it depends on the design of the engiine, I used to have a Volvo MD11C
(in another boat) and it was simpler to replace the impeller in situ - good luck, I guess we all worry a bit
about the impeller!

 

[Guest]

Re: Yanmar impeller

I think anyone who owned a Yanmar 1gm10 five years ago still has nightmares about this problem. I went through TEN impellors in a very short time and did eventually receive a refund as they did admit to a QC problem.
The only benefit was that I learnt to change them very quickly, at sea and under severe stress!
I believe this problem was solved by Yanmar.
Do not consider trying to re-glue them.