Stainless or mild steel into alloy?

Tinkerer

Senior Chief Petty Officer
Joined
Mar 15, 2003
Messages
760
Have to make a no-longer-supplied shaft for the tilt bracket on my 1967 Evinrude 60 HP V4, plus a foot long bolt for the bracket because I can make it in mild steel for about $4 instead of $80 for a new part.<br /><br />I know stainless is best in theory, but looking at the table of active/inactive metals http://corrosion.ksc.nasa.gov/html/galcorr.htm <br />stainless is way up the other end from aluminium while mild steel is pretty close to it. This means that galvanic corrosion is going to be a lot worse with stainless and attack the alloy, while straight salt water corrosion is going to be a lot worse with mild steel and attack the steel.<br /><br />I'm thinking I'll do it in mild steel (not least because I don't have tools to cut threads on stainless) and give it a good coat of fish oil or some other corrosion fighter and grease it up, then pull it apart every year as part of the layup process and clean out any corrosion that's appeared. <br /><br />Any thoughts?
 

G DANE

Commander
Joined
Nov 24, 2001
Messages
2,476
Re: Stainless or mild steel into alloy?

I think you´l be fine with mild steel. the trim adjustment pins wear´nt stainless before 1980 on OMC´s Rusted some though, but lasted for many years.
 

ob

Admiral
Joined
Aug 16, 2002
Messages
6,992
Re: Stainless or mild steel into alloy?

While I think you will be fine with mild steel for the application of your project ,I don't think that galvanic corrosion will be as much of an issue as you may think.After all the bolts that retain the lower units on most every outboard are stainless steel,and a few carefully placed sacrificial anodes and a quality no-oxide grease on the threads work wonders,particularly in saltwater applications.<br />Also, there are no special dies necessary to cut threads in stainless material, but rather slower cutting speeds and die lubricant to prevent galling.
 

FlyBoyMark

Ensign
Joined
Apr 14, 2002
Messages
934
Re: Stainless or mild steel into alloy?

The type of stainless has a great deal to do with all of this....use 316 based alloy for ANY marine application. It is a nickle based stainless and not chromium based.....Chromium based WILL rust and react, nickle based will not. Chromium based alloys are: 400 series, and 304, 302, 310....
 

Paul Moir

Admiral
Joined
Nov 5, 2002
Messages
6,847
Re: Stainless or mild steel into alloy?

About the foot long bolt - I had the same problem as you, but I did find 6" ss bolts, so I got them and a ss coupling nut (a very long nut). I drilled through bolts & nut together and wired through them with ss wire so they could not come loose. I guess non removable strength (red) loctite should do the same.<br />The original bolt was mild steel btw.
 

Tinkerer

Senior Chief Petty Officer
Joined
Mar 15, 2003
Messages
760
Re: Stainless or mild steel into alloy?

Thanks all for that great advice.
 
Top