Bolt Material

[corruptibleseed]

Hi, I'm waiting on parts for my outboard so I got to wondering...

I noticed that the mounting bolts for the lower trim and tilt pin on my Yamaha F60T do not appear to be stainless steel. A mechanic who has been helping me out told me that they are in fact galavanised steel so as to be more corrosion resistant and to prevent a reaction with the stainless steel pin and so cause galling or a fusing of the bolt in the pin.

I always thought it was the reaction between different metals that caused seizing. Or is the Zinc of the galvanised layer immune to this?

From what I gather online, stainless steel is almost always stronger and more corrosion resistant. Just wondering why Yamaha would used a galvanised bolt for this location that is often submerged and for which some strength is required. Thinking back, there are a number of galvanised bolts in the outboard. Just wondering why Yamaha would spec these instead of a presumably longer lasting stainless steel one. Is it just about cost?

Having said that, both bolts on the pin came out without too much difficulty despite not having been touched since they left the factory almost 13 years ago! There was some corrosion on the bolt head itself, but the bolts themselves were pretty ok. I'm replacing the bolts because they're not expensive and to ensure that they can still come out easily after another 13 years.

[boscoe99]

It is a balancing act.

Strength, corrosion resistance, galling, dissimilarity of metals, cost, maintainability, reliability, longevity, etc. are just a few of the variables that enter into the equation as to what to use.

The engineer(s) deciding what to use will all be second guessed by other engineers. I retired from an aircraft company (not an engineer) but oh the fights that would ensue when it came to deciding upon design. What should be used, where it should go, and so on and so forth. Put 10 engineers in a room and there may be 10 plus suggestions as to what must be done. And how.

[corruptibleseed]

Thanks boscoe99. Was just wondering if there was some simple methodology to the decision but I guess not!

For what it's worth, the bolt has held up very well so I guess the Yamaha engineers got that one right.

[ausnoelm]

Stainless bolts are not as “strong” as mild steel……..stainless has very low sheer strength.

[corruptibleseed]

Thanks ausnoelm. That's interesting.. always wondered about that because while I have found stainless steel fish hooks to be softer than steel ones, a stainless steel bolt is more painful to drill out.

Guess there are quite a few variables at play other than just the material choice alone.

[ausnoelm]

Stainless is easy enough to drill if you go about it the right way, a quality drill, cutting fluid and low speed will see stainless drilling easy, try drilling fast and it will just burn the drill point. That said, there is lots of different grades of stainless, and there is certainly a place for stainless bolts, but not in all applications.