Muff Coupler Question

[neildeb2]

Hi all,

Our 58LRC has the 2-prt hafts. I dove on her to replace zincs and discovered a couple of the bolts clamping the muff couplers together. Can anyone help me with answers to the following questions?
1. What size/spec bolts and nuts do I buy to replace them?
2. How is it that bronze muff couplers can bolt to stainless shafts without dissimilar metal corrosion?
3. Similarly, how do SS bolts not produce dissimilar metal corrosion (or is this perhaps why the bolts are missing?)
4. Has anyone else had this happen to them?

Thx,

Neil

 

[Boatsb]

Pull the boat and have it fully inspected. This is not a diy in the water project.

 

[dsharp]

The dissimilar metals will cause corrosion. That is the purpose of the zinc. It is the sacrificial metal that protects the bronze muff coupling. I don’t remember the dimensions of the bolts or whether they were stainless or silicon bronze. We switched over to 1 piece shafts .

 

[Photolomy]

On my stbd side, the coupler is longer than on my port side, and takes 12 bolts, versus 8. But it only has 8 (the ends do not have bolts). The section with 8 bolts is as long as the coupler that only takes 8 bolts. I also have a 3rd coupler (spare) that is just like the port (8 bolts).

I doubt the bolts corroded away, or you would see major corrosion on everything. Also, corrosion isn't about dissimilar metals touching. It is about dissimilar metals in water. Without water, you can't have the galvanic chemical reaction. And as the previous poster said, zincs will corrode first because they have a lower electronegativity than bronze or stainless. And bronze would probably go next.

The following two photos show the 12 bolt version vs the 8 bolt version. I assumed that the PO only used 8 bolts in the 12 bolt version. I can look to see what size they are (in the spare). These are 2" shafts, is that what yours are?

 

[jim rosenthal]

You can probably find 316 SS bolts, washers and Nyloc nuts at McMaster.com.

While there may be some dissimilar metal corrosion, it's probably at such a slow rate it doesn't have much effect. It's more likely the bolts weren't tightened correctly to start with, or worked loose over time. One piece shafts are better from a balance and straightness standpoint, but the expense would be considerable.

As long as you have proper zincs on the boat, the amount of dissimilar metal corrosion where the couplings meet the shafts will be very small indeed.

 

[neildeb2]

The following two photos show the 12 bolt version vs the 8 bolt version. I assumed that the PO only used 8 bolts in the 12 bolt version. I can look to see what size they are (in the spare). These are 2" shafts, is that what yours are?

[/QUOTE]

Thanks for the good info. Yes, mine are 2" as well. If you wouldn't mind looking I'd appreciate it.

Neil 3603059384