shaft anode fit

gasdave

gasdave

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Today I removed my worn shaft anode and purchased a replacement (MG Duff) from my local chandler. I measured the shaft (25mm), checked the internal diameter of my old anode (25mm) and bought a nice shiney 25mm MGD anode.

When I tried to fit my new anode I discovered that there was no way this would fit tightly around my shaft :o. Once tightened as much as possible there was a gap of at least 3mm between the two halves of the anode. I wasn't happy with this as it also meant not much screw thread had passed through the nut. The old one fitted perfectly but I can't tell what make it is!

So I had a look at someone else's - similar fit.

Is this normal? Should the anode not fully encircle the shaft? Do I need to visit my chandler again with my receipt?
 
I renewed my shaft anodes too about 3 weeks ago. It is critical that the shaft sizing and anode are correct. You need to use a caliper to check precisely. Once established the appropriately sized anode should fit snugly and evenly around the shaft to try and ensure wt distribution is even and avoid any uneven heavy spots that may cause a shake (like an out of balance wheel). Shaft anodes can easily come loose too. Its worth studlocking the bolts too just as a precaution. Have a look at www.zincsmart.com you may find them better value than a chandlery - they are very helpful on the phone if you want advice.
 
Are you quite sure the shaft is 25mm rather than 1 inch? The difference in fitting is quite significant and might result in the situation you describe.
 
I have always found that the shaft anode needs 'encouragement' to fit around the shaft snugly in the form of a hammer. On asking the yard engineers thay told me it the anodes are made that way to ensure a tight fit.

A also use a dab of locktight on the ends of the screws to keep them in place. I also use a stainless jubilee clip aft of the anode in case the anode works lose and moves backwards to cover the cutless bearing and starve it of water. The clip is fixed very tight against the anode and I've never had a corrosion problem with them.

Of course, the anode must be the correct diamater for the shaft.
 
Like Piers I use a heavy hammer on one side to support the shaft and hit the other side to ensure a tight fit. Its surprising how much the screws take up.

Also second the Loctite, and I then apply a small dab of antifoul to the screw heads. This stops the screws coming loose through erosion around them. My boat came out of the water yesterday; the anodes were well worn but the screws were still tight.

Zincsmart work for me too.

PS anyone notice that if you search Google with 'zincsmart' an MG Duff advert appears. Sneaky, huh!
 
I bought a 25mm anode for our 1 inch shaft last year because I reckoned there couldn't be much difference - just 0.4mm, and we couldn't find a 1 inch one when we needed it! I had exactly the same problem as you did, so I am sure that's your problem. However, I wasn't going to admit defeat, and forced it into a decent fit. It worked fine, but I won't buy a 25mm one again!
 
Use two hammers to tap the halves together gradually tightening the bolts as you go. It.s surprising how much it will pull up like this. You want a very good snug fit to avoid it coming loose.

Yoda
 
Sounds like a 25mm vs 25.4mm (1 inch) problem. You simply can't tell the difference by looking or holding a ruler against the shaft. You either need to know (from the boat spec) or you need a vernier to measure it. Trial and error can be expensive: zinc isn't that strong and forcing a 25mm anode onto a 25.4mm (1 inch) shaft could split it.

I suppose once you discover it would be worth writing a note in the engine space (in something permanent, like paint) to say which size the shaft is.
 
I just checked some photos of a new 1 inch anode on my 1 inch shaft. There is at least a 3 mm gap between the two halves. As has been said by many posters above, bang the two together and much of the gap will take up. And it won't come loose during the season. I have never used Loctite on mine and never had one come loose in over 20 years.
 
gasdave said:
Today I removed my worn shaft anode and purchased a replacement (MG Duff) from my local chandler. I measured the shaft (25mm), checked the internal diameter of my old anode (25mm) and bought a nice shiney 25mm MGD anode.

When I tried to fit my new anode I discovered that there was no way this would fit tightly around my shaft :o. Once tightened as much as possible there was a gap of at least 3mm between the two halves of the anode. I wasn't happy with this as it also meant not much screw thread had passed through the nut. The old one fitted perfectly but I can't tell what make it is!

So I had a look at someone else's - similar fit.

Is this normal? Should the anode not fully encircle the shaft? Do I need to visit my chandler again with my receipt?
Click to expand...


If this is on your Sadler, it has a 1 inch shaft, not 25mm. Trip to the chandlers and a bit of humble pie!
 
Thankyou everybody for replies - and especially Tranona for checking me out :cool:

I did wonder about the 1" vs 25mm issue but (obviously carelessly :o) didn't think it would make such a difference. We live and learn! As I haven't banged it with a hammer yet I ought to be able to swap.
 
Tranona said:
How would such brutality help? The anode he has is too small and he is going to get the correct one!
Click to expand...

Some follow-up .......

I swapped the anodes today and have now fitted the "correct" 1" one - there is still a bit of a gap between the two halves, although less than before :mad:

Apart from this gap the fit elsewhere is perfect with excellent apposition to the shaft. It is screwed well tight. I am tempted to not resort to violence to encourage any more tightness. Does this seem reasonable?
 
There are two crucial dimensions to a shaft anode. The shaft diameter and the residual gap, which there is no reason to suppose is zero when the fastening screws are tight. Just because there is a residual gap, it doesn't follow that the fitting isn't snug: they have just sold you a little less zinc.

In fact if the gap was zero you couldn't guarantee tightness on the shaft.

44769822.jpg
 
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