Engine bolts

I am planning on remounting the engine on my Zodiac 470 RIB. I was at the store looking for the right size replacement bolts. While talking to the guy there, I said I wanted stainless steel bolts (size M12). He said I should use hardened steel bolts to mount the engine, not stainless steel.

I figured that the bolts should be stainless for corrosion protection. The nuts on the current bolts are stainless. I assumed that the bolts were stainless too, so I didn't really check them.

The motor is a Yamaha 40 4-stroke outboard. The boat is mostly used in fresh water, but I can't say that it will never be used in salt water.

Which bolts should I use?

Re: Engine bolts

Grade 5 zinc coated, with matching Grade 5 fasteners and hardened washers. Stainless is not strong enough.

Re: Engine bolts

Looking around the web, I find that the tensile strength of 18-8 stainless bolts are very close to the tensile strength of grade 5 bolts.

See
http://www.tessco.com/yts/customerservice/techsupport/whitepapers/pdf/bolt_grade.pdf

http://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

I am using 1/2 (M12) bolts.

Re: Engine bolts

there is a 40ksi-80ksi window (or a 40ksi swing) on 18-8 stainless bolts because the strength is not controlled like a set of grade 5 or grade 8 bolts. The corrosion properties are controlled. The material properties are a crap shoot.

use what you want if you dont want advice.

if your worried about corrosion, try these http://www.mcmaster.com/#catalog/118/3138/=h2b8ds

Re: Engine bolts

Well im suprised to read this.
I dont want to be up setting the apple cart or be seen to be dis - agreeing with anyone but here is my thoughts on this.
Ive recentley contacted a BRP main dealer about engine bolts for my 60hp evinrude, they told me that i would be
needing to use stainless steel bolts due to my boat being often used in salt water.
They didnt have any in stock, and i asked several other marine engine dealers and got told the same thing, even though most
all of them had steel bolts in stock, they all agreed i would need stainless steel, and all gave me numbers of other outlets to try to get them.
I am having trouble getting hold of stainless bolts in 5 inch long by 1/2 inch or 13mm diameter...

Now it seems i can use steel bolts after all, but what about the corrosion effect ?
I realy dont want any rust marks on my boat, and dont want any corrosive effect on the engine bracket.
I have always in the past used stainless and never had a problem from small 4 hp upto v4 outboard engines.

im now not sure what to do about bolts, and what grade i need to get here in the uk.



phill