And another bolt thing

[Techno]

I was adding up what I needed to get in fasteners for my partial re-rig and guess what I discovered purely by accident, Brass nyloc nuts on all but the two steel bolts for my OB and jack plate. I have taken the OB off twice and the jack plate once and never noticed them. I couldn't believe it so I scratched them and they are brass.
If it wasn't for the two steel bolts I wanted to replace I probably still wouldn't have noticed, I was checking to make sure the SS bolts had SS nuts and not steel.
So I have stainless steel, aluminum, and brass all touching, I wonder what kind of reaction this makes.

On my last boat I used grade 8 socket head bolts for the plate. sometime later I removed a bolt and found that half of the bolt was gone, the aluminum hole was slightly larger but not much. I don't know if the aluminum wore the bolt or if I made a battery and it eroded the bolt. This is one reason I like the pipe through the transom method. I can remove one bolt and check it out.

[FCnLa]

It's call dissimilar metal corrosion. All you can do is coat the bolts in something (like a good epoxy). To my exprience stainless to aluminum will do it very little or none at all. I don't recall any problem with brass. Magnesium and aluminium will do the same thing as aluminium and steel.

[Raceman]

On the early V6 mercs there was a hollow stainless bolt in both sides at the bottom through the transom. These were the factory bolts and the power trim hoses fed through them. All the early V6's were made this way. They also had stainless lock nuts on the inside. Trouble was, monkey wrench Joe down at the marina wasn't smart enough to use anti seize, or run em on by hand. The impact wrench got em hot enough to gaul. A lot of em had to be cut off which was a mess. Merc shortly changed over to brass nuts and fixed the problem with the gauling. Far as I know they stayed that way until they changed to the industry standard bolt pattern, or at least to the trim pump on the clamp brackets.

[steve]

Stainless is not effected by the reactions that non SS steel is. However SS will gall if you use SS nuts AND bolts. Thats why Allison and other boat builders use brass nuts. I prefer grade 8 steel and grade 8 nuts. My motor is off and on enough that they never rust . If you notice, plain grade 3 bolts are not much weaker then SS is in psi rating. Grade 5 is slightly stronger. 8 is best. If you use SS on SS you can use Anti Sieze on the threads.