Heli-Coils in Fiberglass. Anybody Done This?

[skiguy]

The front tracking fin on my 05 22v fell completely off a couple weeks back. I’m looking to mount a new one but have determined that the existing threads in the mounting holes are damaged as I cannot get at least 2 of the replacement bolts to thread and tighten. It looks like the factory used self tapping screws to hold the existing fins in - an odd choice as I wouldn’t think the hold strength would be all that good.

A friend of mine recommended heli-coils and I’ve researched this a bit and can’t find any really good references on how best to mount the heli-coils in fiberglass. The bolts are 3/8-16. Normal installation of heli-coils in steel or aluminum have you drilling the hole slightly larger, tapping and then screwing in the inserts. I have my doubts that tapping fiberglass will leave useful threads, but I could be wrong.

I’m hoping some folks on here have some experience in this type of repair and can offer some insight on the best way to proceed.


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[chpthril]

There is a 2-part product for repairing threaded holes so they can be re-drilled/threaded. Then rebed the fin with 5200

[UNSTUCK]

Coils require drilling and tapping the parent material and then threading the coil into it, taking the hole back to the original size. I don’t see you drilling and tapping the fiberglass.

Instead see if you can run a bolt through the fiberglass and using a nut and backing plate on the inside.

[lee]

Fill the hole with Marine Tex and redrill for the screw.

[KoolAid]

Just remember the fuel tank is right above it and your year model may be one of the ones with a plastic tank. Be very careful when drilling.

[skiguy]

Just remember the fuel tank is right above it and your year model may be one of the ones with a plastic tank. Be very careful when drilling.

Thank you! You are correct. It’s an aluminum tank and it’s impossible to remove without yanking the vdrive AND the tranny. Something I would have done if at all possible to put backing plates in place. I will definitely be extra careful.

I think I’ll go the marine-Tex putty route, drill and re-tap. Lots of people have good things to say about that stuff.


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[gumby]

The tank will not come out without removing the drive? That doesn't seam right. It might be true. I am really curious, thoughts?

[skiguy]

The tank will not come out without removing the drive? That doesn't seam right. It might be true. I am really curious, thoughts?

I took a good long look at it last week. It’s too wide to be turned sideways and lifted out - the welded on mounting brackets insure that. The front of the tank is a good 12-14 inches forward of the front opening of the floor hatch and there’s a 8-10 in. tail on the rear-strbd section where the fill and vent lines connect that is next to the vdrive and inches away from the tranny. It looks to me like the tank was installed before they dropped the motor assembly in.


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[gumby]

Don't take my post wrong. Because i have no idea if it would come out. I know the vent line on mine is on the front and I thought to my self that it would be a bummer to get it off to get the tank out. Mine also has the bump for the fill line.(38 GAL) I was kinda asking because thought there might be someone who has removed one. Or tried to.

[skiguy]

I may be over thinking this but I’m not sure how much adhesion the Marine-Tex will have on the walls of these approx 1/2”w x 3/4”d (when drilled out) vertical holes. I won’t be able to compact the epoxy putty against anything to fully fill the holes, opening the possibility of air pockets and poor contact with the sides of the holes. But I’ve never worked with Marine-Tex so folks who have may be able to confirm this is the right way to do this job.

Taking a look at Threaded Inserts again. I ran across these. Your thoughts?

http://www.rivetnuts.com/threaded-inserts.htm




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[chpthril]

Id be worried about those blind nuts spinning in the fiber glass. As soon as that happens, game over.

[lee]

Marine Tex will be like peanut butter, pack it in the holes then tape waxed paper to the bottom to keep it in the holes until dry

[NICKYPOO]

I used marine Tex to fill the holes from my old speedo pickup assemblies and it is some really hard stuff once dry. It will expand just a bit as it dries so it should get pretty far into the old stripped out areas. The only real problem with the stuff is that gelcoat won’t stick to it. I still have to figure that part out.

[IDBoating]

I'm absolutely not an expert on threading fiberglass , but no matter what the factory did I'd want to move to bolts and backing plates. Screws in fiberglass? Maybe for a speaker, but not for the forces on a tracking fin. Yowza.

I realize from the comments that accessing the inside keel area may be a bugger given the fuel tank, but it sure feels like you'll just end up redoing this again in the future - possibly with even greater damage to the integrity of the fiberglass in that area. My (plastic) fuel tank has access holes through which the fin mounting hardware can be accessed, but I presume yours doesn't or you'd have mentioned it.

Rather than taking out drivetrain components just to remove the fuel tank, I'd be tempted to lengthen the access hole in the floor of the boat so the tank could be tilted more and then removed. A properly sized piece of Starboard with the carpet glued to it (or even the original floor panel) could be used as the hatch, and aluminum angle could create two rails that, if desired. would take screws to hold down the new floor section. I suspect you wouldn't need screws, though... friction fit would probably do it, along with a small piece of flat aluminum on the rear edge to hook under the existing floor hatch. Lots of options that don't involve removing the engine and/or transmission.

[skiguy]

I'm absolutely not an expert on threading fiberglass , but no matter what the factory did I'd want to move to bolts and backing plates. Screws in fiberglass? Maybe for a speaker, but not for the forces on a tracking fin. Yowza.

I realize from the comments that accessing the inside keel area may be a bugger given the fuel tank, but it sure feels like you'll just end up redoing this again in the future - possibly with even greater damage to the integrity of the fiberglass in that area. My (plastic) fuel tank has access holes through which the fin mounting hardware can be accessed, but I presume yours doesn't or you'd have mentioned it.

Rather than taking out drivetrain components just to remove the fuel tank, I'd be tempted to lengthen the access hole in the floor of the boat so the tank could be tilted more and then removed. A properly sized piece of Starboard with the carpet glued to it (or even the original floor panel) could be used as the hatch, and aluminum angle could create two rails that, if desired. would take screws to hold down the new floor section. I suspect you wouldn't need screws, though... friction fit would probably do it, along with a small piece of flat aluminum on the rear edge to hook under the existing floor hatch. Lots of options that don't involve removing the engine and/or transmission.

The existing tracking fins look to be factory mounted with self tapping screws - as best we can determine from peaking under the tank with a mirror. There are no backing plates with the factory install. I suspect they are bedded with 5200 as well as the screws.

I’m not sure lengthening the hatch would help unfortunately. The welded-on mounting brackets on the tank are wider than the access panel and would keep me from either tilting the tank to gain access to the fins or lifting it straight up and out. That was my first option and I gave it a good long look before looking at other options.

It looks to me one would have to cut the mounting brackets close to the tank to even have a chance of getting it out.


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