Kicker bracket bolts

[redlinj]

In the process of mounting a homemade 1/4 in. aluminum fixed kicker bracket on my '82 Grady White i/o. The bracket is 14 inches long. The kicker is a 9.9 yamaha weighting in at 130lbs. Yes, heavy indeed! Plan right now is to use 3/8 by 3 1/2 inch 18-8 stainless bolts. Since the kicker will be sticking out a bit, there will be a lot of downward force exerted on these bolts especially when underway with the main 5.7 engine. There will be 6 bolts, 4 on top and 2 near the bottom of the bracket. Will they be strong enough? Thanks!

 

[R055]

Use backing plates like people use for wakeboard tower installs. That's crazy force on it when your driving down the freeway and hot a hole or bump.

 

[Lowlysubaruguy]

My two cents worth for what its worth. First stainless has its place and then there are places that its not best placed. It does not hold up to certain forces. Its also prone to thread distortion which causes a variety of issues one most common is siezed nuts that result in breakage when removed or more so in your case if you feel the need to tighten them up when they loosen. While they are hard they are not as strong as many other bolt options the longer and more vibration there put under the better chance for failure. I hang my 9. 9 yamaha on a 20 foot aluminum boat and work the devil out of it. The bracket is 1 1/4" thick and it mounts to a 1" piece of aluminum. I started with stainless bolts there about 3" long the first time they came loose I broke one or two tightening them. Thats when I found out about stainless. Theres special lubes to prevent thread distortion and they should be installed by hand without tools that produce any friction like impacts. I have been using the same metric probably zinc plated 10mm bolts for over 10 years Im thinking I made the bracket in 1998 and did away with stainless by 2000 Ive replaced them a couple times but I take this bracket off for summer boating and re sintall it when im trolling in the spring and fall. I use nylon lock nuts and thick washer on each side. So my vote zinc grade 8 or better 3/8" or 10mm with matched nuts ( get coated grade 8 or better lock nuts as well) and washers price will be 20% or less than stainless and they will outperform them for this purpose. Dont get my wrong theres places for stainless. Just not here.

 

[redlinj]

My bracket is 1/2 in. aluminum not 1/4 as I stated in my 1st original post. Went out and purchased 7/16 stainless bolts yesterday, however may exchange them today for zinc coated. From my research I've found that even grade 5 is still a whole lot stronger than stainless. Was hoping stainless would hold up, and maybe it would, but now hate to take a chance! Any other opinions?