Outboard anode fixing?

[KevinV]

I was a bit surprised that the anode on my outboard is attached with a stainless bolt. This has led to corrosion of the bolt hole - not new as it has a tiny helicoil in it already. I can rethread at m7 or 8, but should I use an alloy bolt? Or stick with stainless but do a better job of isolating it?

 

[KevinV]

Picture of the corroded hole:

 

[vyv_cox]

The anode on my Bruntons Autoprop is attached with two nylon bolts that were supplied with it. This prevents premature loss of the anode zinc around stainless bolts.

 

[KevinV]

The anode on my Bruntons Autoprop is attached with two nylon bolts that were supplied with it. This prevents premature loss of the anode zinc around stainless bolts.

Ah, a nylon bolt would make better sense. Should I then put dielectric grease behind the anode to make good contact with the paint?

 

[vyv_cox]

Ah, a nylon bolt would make better sense. Should I then put dielectric grease behind the anode to make good contact with the paint?

Probably a good idea, although I only abrade mine. Better to have no paint I would have thought, metal to metal contact.

 

[VicS]

I was a bit surprised that the anode on my outboard is attached with a stainless bolt. This has led to corrosion of the bolt hole - not new as it has a tiny helicoil in it already. I can rethread at m7 or 8, but should I use an alloy bolt? Or stick with stainless but do a better job of isolating it?

Ah, a nylon bolt would make better sense. Should I then put dielectric grease behind the anode to make good contact with the paint?

I would fit the new anode with a stainless steel bolt as originally fitted. It probably relies on the bolt for electrical connection to the outboard leg especially if the leg is painted under the anode
Dielectric grease is non-conducting so don't be too liberal with it.

Looking at your pictures of the outboard I am wondering why it has suffered so badly. If it is permanently immersed consider adding a couple of small bar anodes to the AV plate.

 

[KevinV]

Looking at your pictures of the outboard I am wondering why it has suffered so badly.

My thoughts exactly, I think it's only been used one season, perhaps two and in fresh water - BUT the anode is zinc - I thought that was only for saltwater? On the other hand the anode has been eaten away, front and back. I'm confused.

 

[VicS]

My thoughts exactly, I think it's only been used one season, perhaps two and in fresh water - BUT the anode is zinc - I thought that was only for saltwater? On the other hand the anode has been eaten away, front and back. I'm confused.

You are right, zinc is only for saltwater
Aluminium for salt or brackish
Magnesium for freshwater, but I don't know if you can get Mg anodes for outboards

 

[thinwater]

Ah, a nylon bolt would make better sense. Should I then put dielectric grease behind the anode to make good contact with the paint?

If there is paint and a nylon bolt you might as well skip the anode.

It does not matter how liberal you are with the grease; the bolt pressure will push it aside. Try grease on your meter and note that it has no effect on continuity, at even the lightest pressure. The only times it maters are high voltage, low amps, like radio or ignition.

Normally tipping the motor up is most of what an outboard needs. The rain rinses off the salt and then it dries, so there is no conductivity around the anode. Zincs can often last the life of the motor.

 

[KevinV]

If there is paint and a nylon bolt you might as well skip the anode.

It does not matter how liberal you are with the grease; the bolt pressure will push it aside. Try grease on your meter and note that it has no effect on continuity, at even the lightest pressure. The only times it maters are high voltage, low amps, like radio or ignition.

Normally tipping the motor up is most of what an outboard needs. The rain rinses off the salt and then it dries, so there is no conductivity around the anode. Zincs can often last the life of the motor.

Problem being that this one lives in a well - there's no tipping it up

 

[thinwater]

Problem being that this one lives in a well - there's no tipping it up

Ahh.

Then I would stick with the SS bolt, but use either waterproof grease, Lanocote, or seacock grease on the bolt. I would also remove the paint and grease between the anode and the alloy. The problem with a helicoil in this application is that it is concentrating the current at the coil/alloy interface. A through bolt would have been the best choice.

 

[QBhoy]

All mercruiser and mercury come like that from factory.