Rivnut or helicoil to repair bolt thread?

[SteveTibbetts]

Bolt for the mast gate dropped out and it looks like the hole has de-threaded. Never used either a rivnut or a helicoil and don't have tools for either. I can buy a helicoil kit for just over £20.
Any suggestions? Helicoil looks like it might be easiest? Bolt looks like m8, but I'll not be able to check until I get back to the boat.


Steve

 

[VicMallows]

I can't see a helicoil working in a thin mast section? A rivnut should be fine.

Edit: What exactly do you mean by 'mast gate' ? I am thinking of the spring-loaded slot you feed the mainsail sliders into.

 

[alahol2]

I tapped mine out to the next size up. Slot in the gate was big enough. I used a normal hex head machine screw rather than a thumb screw but it's only unscrewed twice a year.

 

[SteveTibbetts]

I can't see a helicoil working in a thin mast section? A rivnut should be fine.

Edit: What exactly do you mean by 'mast gate' ? I am thinking of the spring-loaded slot you feed the mainsail sliders into.

It's the bit where you undo a bolt and a plate can be moved aside to allow the sail slides in or out of the slot where they go up the mast

 

[SteveTibbetts]

I tapped mine out to the next size up. Slot in the gate was big enough. I used a normal hex head machine screw rather than a thumb screw but it's only unscrewed twice a year.

Thanks! This could work I think. I'll give it a go before spending on special tools

 

[ffiill]

I would second tapping it out-a useful solution in all types of situation.
I would also add that for light use you can get away with a cheap little set of taps m4 to m12 found on e bay et al.

 

[macd]

Thread inserts (which is what I presume the OP means by 'helicoil') are brilliant for many mast applications, the reason Selden et al use them for many critical fasteners into aluminium. But they're not best suited to thin-walled materials. Agree easiest to drill and tap to next size up.

 

[PetiteFleur]

Rivnut is the way to go and no special tools to buy. I have done this for a mast gate just as you want to do. You insert a bolt into the rivnut with a nut between against the rivnut, tap the rivnut into the prepared hole(make sure it's a tight fit so it won't rotate), hold the bolt firmly and turn the nut with a spanner until it collapses the rivnut and is firm, make sure you lubricate between the nut and rivnut.
Helicoils won't work in the thin mast section and are usually used to replace stripped threads in aluminium castings, which is what I had done on my 2.2 Suzuki recently. I can't remember whether I used Monel or Stainless, best to use Monel if you can get them.

 

[LadyInBed]

I have the same problem on my mizzen. I have thought about going up a size but I will first try building up the inside then reducing the hole diameter with Chemical Metal, then use a self tapper rather than a bolt.
If this doesn't work I then still have the option to drill out and go up a size.

 

[Merlin38]

I used an M8 Rivnet to attach a new cleat to the mast. I obtained the aluminium rivnut and a fixing tool via ebay. Easy to do and very strong.

 

[davidej]

Sorry to hijack the thread but I have to fit a new hallyard diverter at the top of my mast.

I know from experience that pulling up a large monel pop-rivit from a bosun's chair is not easy.

Would a rivnut be an alternative - s/s or ally?

 

[savageseadog]

If you up the thread size there may only be a tiny amount of threaded material to hold the screw on a mast. I would suggest a rivnut/nutsert, you can buy countersunk ones. To be quite honest I'm not sure whether I'd go for a stainless or aluminium one, stainless would certainly be better for repeated use but you will need a proper tool to set it.

In answer to the question above a long arm riveter would probably be OK up the mast rather than a lazy tong type. You could use rivnuts which in stainless would be equally as difficult to set.

 

[lw395]

You can set rivnuts by screwing in a bolt or stud, then winding a nut down the stud.
They will also tighten up when you mount the fitting on them.
I'd use a rivnut if the mast wall is too thin to have around 3 full turns of the tapped thread, maybe 2 for a lightly loaded fitting.
If the wall is thick enough to tap a good thread, that's what I'd do.
For serious loads I'd get a monel rivet put in.
For light loads and no reason to undo it in the foreseeable, I'd just rivet the fitting with ali rivets.
In all cases Duralac.
Except perhaps a tapped thread where I might just use plenty of Loctite.

Helicoils are great but you need thick metal to put them in. About 8 turns?
I've used the 'recoil' brand ones on motorbike bits in the past.