Stripped thread

david_e

david_e

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www.touraine.blogspot.com
The butterfly locking nut on my Mariner 3.3 outboard has stripped the thread on the aluminium housing that it screws into.

I am seeking a simple solution & I think that the options are;

1 Get a bigger butterfly nut and re-drill & tap the housing. Problem here is where do you get butterfly nuts?

2 Fill the housing thread with plastic metal or ? and re-drill and tap. Las time I used a form of plastic metal was in 1976 and it was expensive, what is on the market today & where will I get it?

Which is the easier & cheaper option? (I have access to the tools required)
 
The best solution is to use a rethreading tool and coil such as 'Helicoil'. These are not cheap to buy, but most decent engineers or workshops will have a range to suit most threads. The principle is that a special tap cuts a special thread into which a special coil is screwed. The inside of the coil is a perfect thread for the bolt that you just stripped the original thread with. The new thread is often stronger than the original since the coil tends to expand and grip the metal into which it is screwed.

I got a thread mended this way at a motorcycle workshop once. If you can take the thing appart and just present them with the thread to reform, it shouldn't take more than a couple of minutes and a few pounds cash.
 
Thanks John, had forgotten about this option. My Father was a M/cycle dealer for over 40 years and has an array of tools in his garage - I'll bet amongst his taps & dies he has something like this. He isn't too well but this task might cheer him up, any idea where I will get a helicoil?
 
Screwfix do M6,M8, and M10 butterfly nuts, although not stainless .

Otherwise, if you are fortunate enough to have an old-fashioned hardware shop near you, as we have , they may be able to help
 
Helicoil or Recoil or other similar products are on ebay often enough, far cheaper than the merchants. If it's not a blind hole you may need to secure the helicoil with a touch of Loctite I would use the virtually non removable stuff (Studlock is one name they use)
 
If you already have the tools you can buy helicoils from decent engineering factors. I think you may have to buy more than one though.
I reckon your best bet is to take the motor to a mechanical engineering workshop (one that does engines) as they always have the gear, and more importantly, the experience, to fit helicoils.
 
LakeSailor's advice makes the most sense. Recoils usually come in packs of 10 or more, plus you need the special tools, so the cost of the complete job at a small engineering shop (or even an old fashioned m/cycle shop) could well be less. On a marine applications, I'd be inclined to use something like Duralec between the insert and the aluminium to reduce galvanic corrosion, but you'd probably need to supply this yourself. The insert itself is some sort of stainless steel. Incidentally both 'Recoil' and 'Helicoil' are registered trade names. These days the former is more often seen for sale, although the latter is often used as a generic description.

If you want to go the DIY route, Snap-On vans usually carry Recoils. Sometimes they have sets on special offer. I bought a set of inserts and tools in all sizes from 5 to 12mm for about £90. They're well handy to have in stock. Trouble is, you use half of them repairing friend's cock-ups rather than your own.
 
Well you recommended buying the complete kit and I was suggesting he could buy the inserts alone.
Then you recommended trying the local garage and I suggested a couple of other spots that may be able to help.

Don't see a problem with that. (and don't forget, I'm an expert when it comes to being duplicated.)
 
Reading my post again I see that I might have been ambiguous. In my mind I thought I was saying - take it to a local engineers or motorcycle workshops as the kits are too expensive. I didn't mean to suggest buying a kit - they are very expensive to repair one thread! I will retire back into my box now.
 
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