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Discussion Starter · #1 ·
I have a 2004 Honda outboard motor in excellent shape, but many fasteners are corroding. Why doesn't Honda use Stainless Steel for all their screws and bolts? I have been replacing the rusted fasteners with stainless steel parts. I googled the question and did not get the answer to my question.

Thanks,

Steve
 

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Discussion Starter · #3 ·
Perhaps Honda is not using stainless steel to make more money. I have had no issues with the SS products I used on the motor.
 

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Discussion Starter · #5 ·
My suzuki bolts aren't stainless either.
When the bolts start rusting I replace them with ss. They may not use ss fasteners due to galvonic reasons, but in the real world it is very difficult loosening rusted bolts and hose clamps rust away.
 

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When the bolts start rusting I replace them with ss. They may not use ss fasteners due to galvonic reasons, but in the real world it is very difficult loosening rusted bolts and hose clamps rust away.
I have a 2004 Honda outboard motor in excellent shape, but many fasteners are corroding. Why doesn't Honda use Stainless Steel for all their screws and bolts? I have been replacing the rusted fasteners with stainless steel parts. I googled the question and did not get the answer to my question.

Thanks,

Steve
It’s kind of counterintuitive, but combining aluminium alloy and stainless steel fasteners results in greater galvanic corrosion susceptibility compared to same but with zinc galvanised fasteners.

The boring stuff:
That is due to a difference in so-called anodic indexes between those two metal.
For outdoor and marine environments it’s desirable for the difference in anodic indexes (between two metals) to be less then 0.25V.
(BTW, you can google gazillions if web pages with anodic indexes for all metals.)
For the most of aluminium alloys anodic index is about -0.95V and for Zinc galvanised steel is about -1.2V, making them a good pair.
Not so for stainless steels. SS 316L anodic index is about -0.5V. Not a good pair.

Tight lines.
 

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Discussion Starter · #8 ·
I did a little research and found the ss fastener will likely corrode the aluminum threads over time, making them hard to remove. The aluminum threads in the engine can even deteriorate over time. There are materials that can be put on the threads that will slow the corrosion time. Stainless steel screws are used on aluminum gutters due to the ss strength. A marine environment with salt increases the corrosion between the two dissimilar metals.
 

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Discussion Starter · #9 ·
I spoke to a marine mechanic who regularly replaces the original bolts on outboard motors with stainless steel. Over the past 16-years, he has never had a problem with galvanic corrosion. Likewise, the mechanic never had difficulties removing the ss bolts on an aluminum engine, or having the engine's aluminum threads corrode is never an issue. So, I will follow the advice of an experienced marine mechanic. I am sure there is corrosion, but not enough to cause a problem. Selling the OEM fasteners is an excellent way to make extra money replacing the rusted fasteners every few years.
 

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Discussion Starter · #11 ·
Damn!! Ugly, I will show the picture to the mechanic and see what he says. Thanks for posting the photo!
 

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Discussion Starter · #12 ·
SS bolts are only used on the outside of the engine, not on the inside. It's too hot. On the inside of the engine, you use OEM bolts.
 

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because their outboards use powerhead that are basically pulled off the same assembly line as the engines that go in their cars... Hondas & Suzukis are notorious for almost zero corrosion protection... They basically build them to last ~10 yrs in a saltwater environment...
 

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From a material property perspective, most common SST fasteners aren't nearly as strong, and thus cannot be torqued like you would a alloy steel fastener. This torque/bolt preload are very much a requirement in certain locations of an engine (head is the obvious location). Heat shouldn't be any issue with most any SST fasteners. If you want a SST fastener that is near equivalent strength to alloy steel, look into A286 vs 18-8/ 300 series SST that is common.
To take it a bit further, if anyone has issues with SST fasteners, looking to replacing with passivated SST fasteners.
 

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MR2. didnt think those existed anymore! always liked them, hated fixing them.
 
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