Bukh DV20 zinc anode

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frderek

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I'm having a bit of trouble locating this! The manual only shows it on a dismantled engine. It says on the 'front' of the engine but the only candidate I can find is on the gearbox side (is that the front? it certainly is on the stern side!). There is a quite large nut that seems to be bronze or brass. Is that it? If so what size spanner fits it? It's bigger than 19mm which is the largest I have on board a.t.m. If it's elsewhere then please advise :)

tia

Derek
 
It's the one you suggest at the rear (stern) end near the top. It is 22mm. It is partially obscured by the gear selector assembly so that you can only use an open ended spanner unless you dismantle the assembly. If it is tight, on open ended spanner is likely to burr the nut before you free it!

(Personally I question what the tiny anode achieves in the big cast-iron block .... but most disagree and change them endlessly).

Edit: gear selector rather than 'throttle'
 
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Just another input from experience on a similar DV10, and here is the nut on my engine block.

The anodes are a close fit through the hole in the block and the anode 'swells' as it degrades in contact with seawater; removing the 22mm hex nut can simultaneously unwind the anode's threaded spigot which is screwed into the inner face of the nut, leaving the anode jammed in the hole.

When I first encountered this problem the nice people at Bukh said " simply tap it through into the waterway in the block where it can safely lay and continue its good work as the water gallery is plenty big enough not to be blocked".

However, getting a good enough swing in an inaccessible position with nothing heavy enough to achieve the objective I had to give up that idea and so made an extractor. Once again due to being unsighted (the engine was a tight fit in its bay) and for fear of bearing down on a breakable component where a safe purchase wasn't easy, that failed too.

It was not possible to remount the hex nut back onto two different size threads i.e. the threaded block and the threaded anode, so I was left with the problem of resolving the threat of water ingress to the boat and clearly it couldn't be left that way.

My solution was to drill out the inner thread of the nut thus allowing the spigot clearance inside the nut which in turn meant only have to mate the nut's coarse thread to the engine block and achieving a watertight solution. I had also purchased a brand new nut as these are brass headed and the tricky job of getting a purchase with a large 22m open ended spanner had caused a bit of 'rounding' to the nut faces to a point where pretty soon this would cause future problems on removal; this nut with a new anode is used whenever (upon annual inspection)the old anode has either disappeared through erosion or can be tapped through.

Finally, since a 22mm spanner is a whopper and I didn't have clear access to wield it without fouling another part of the engine or the electrical circuitry, I had to cut down a standard spanner to about half length.
 
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I just reduce the diameter of the anode in a lathe but if you don't have a lathe you could file it down.
 
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