Engine Bracket Bolt Sealant

[Jason2tpa]

Man oh man...When I started this thread I truly thought there would be a consensus for such a simple task of sealing engine bolts.

We've got the pro marine mechanic suggesting:
*toss silicone sealant overboard
*not to use 5200 because of its shear strength
*4200 is what he suggests

We've got the retired lockheed aviations mechanic suggesting:
*use marine silicone sealant
*No need to use 4200/5200 because these are adhesives

And we've got the majority of other replies suggesting NOT to use 5200, using a marine silicone sealant will do the job.

Even though there seems to be no definitive product to use, you'll all provided some good thought provoking insight.

[Jason2tpa]

Not a big fan of 5200 either. Seems like it shrinks some when it dries in addition to being a mess.

I have screws to secure fiberglass surfaces to other fiberglass surfaces. For example, the console is screwed into the deck. Bunch of screws and they always work themselves loose. I wonder what the best choice would be for a non-permanent Loctite type sealer to keep this from happening?

Shrinking occurs when you insert screws into over drilled pilot holes filled with 5200.

Before I installed my leaning post onto the deck I did some research on what adhesive product should be used. I spoke with a few boat builders I know, a few companies that manufacture leaning posts, etc. The overwhelming consensus was to use a permanent marine adhesive, such as 5200. Yes, it could become a pain if you ever want to remove the screws, emphasis on could. What will happen in due time if you do not use such a strong adhesive is the loosening of the screws. A tremendous amount of physical forces are applied to deck securing screws while underway. Rough seas, even more. These forces will eventually loosen the screws if not literally anchored into the deck. If you had to remove something from the deck that was secured with 5200, there are successful techniques to use...such as using pinpoint heating.

Now, I can tell you with certainty that most people tend to overdrill the pre-drilled pilot hole. They do this because they don't want to risk cracking the fiberglass by drilling a small pilot hole, then screwing in a substantially larger screw diameter. Problem is the larger the pilot hole you drill for a given screw diameter, the pull out strength of that screw becomes less and less.

Ideally you want to use the smallest pilot hole possible, preferably the same diameter of the screw shank, thereby allowing the screw threads to dig in their entire thread wide into the deck. This is termed "purchase". So for your job, fastening the console to deck, squeeze out some 5200 into a piece of cardboard. Twist each screw into the 5200, completely covering the entire screw body with 5200. Then take a paper towel or cloth and twist the screw onto the towel, removing excess 5200. At that point the 5200 should only be in-between each thread, not on top of the threads. This will prevent excess 5200 to squeeze out of the drilled hole when you're screwing in, which would adhere the underside of console to the deck surface.

If you are methodical and careful, this is not a difficult task to take on. Go about it recklessly and you'll either crack fiberglass or the screws will pull out. But no doubt, 5200 is the end-all be-all adhesive to use for this task.

[Sequoiha]

NEVA EVA use silly cone.

at a minimum boat life caulk.

silicone has no shear strength and will leak soon.

about the best thing to do with silly cone for marine use is toss it off the bow.

Personnel preference, been doing this for 30 years, never had a problem. When the mounting bolts are tightened correctly and more important checked and tightened during maintenance,