Repairing threaded hole in saildrive bed.

PaulRainbow said:
You'd need to tap the holes in the GRP Richard. I think if you epoxied them in, allowed the epoxy to set, then ran a M5 tap through the Helicoils they would work well. Remember to snap the tangs off, the bolts will force the helicoils out, as you describe.
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That M5 tap into the epoxied helicoil sounds like a great idea, thanks. This should allow me to use the existing holes even in they've been a bit "extended" by the previous dodgy fitting process. I'll still use nuts and washers on the four bolts which I can access as I just prefer something "solid" but I'll buy 8 helicoils for the others.

That's another job which has shifted up the list a couple of places!

Richard
 
RichardS said:
That M5 tap into the epoxied helicoil sounds like a great idea, thanks. This should allow me to use the existing holes even in they've been a bit "extended" by the previous dodgy fitting process. I'll still use nuts and washers on the four bolts which I can access as I just prefer something "solid" but I'll buy 8 helicoils for the others.

That's another job which has shifted up the list a couple of places!

Richard
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Epoxy won't work well with Helicoils Richard.
For epoxy to work it requires a glue gap to the bond surface. Because a helicoil is a larger diameter than the female thread it is being fitted to, any glue will be squeezed out between the coils of the insert. The remaining glue will be cleaned out by the tap you run down to clean out the inside of the insert, leaving no bond.

Fit them correctly, you won't need to bond them, you're obviously technically savvy, as long as you cut the threads properly and use the correct tool to fit the inserts, I'm pretty sure that you won't have a problem.
 
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prof pat pending said:
Epoxy won't work well with Helicoils Richard.
For epoxy to work it requires a glue gap to the bond surface. Because a helicoil is a larger diameter that the female thread it is being fitted to, any glue will be squeezed out between the coils of the insert. The remaining glue will be cleaned out by the tap you run down to clean out the inside of the insert, leaving no bond.

Fit them correctly, you won't need to bond them, you're obviously technically savvy, as long as you cut the threads properly and use the correct tool to fit the inserts, I'm pretty sure that you won't have a problem.
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I think that the problem is going to be that the GRP has already been tapped to take the M5 helicoils ..... but as these seem to be falling through I think that the GRP threads will be somewhat stripped so I suspect that I'm going to need fix the helicoil somehow.

I can't drill out to M6 and re-tap as I need to use the current M5 bolts as they are the correct size for the fittings (it's the three louvres which fit right across the front windows). I could drill out the louvres and enlarge the countersinks to take M6 but that's getting a bit involved so I'm trying to avoid it.

Richard
 
RichardS said:
I think that the problem is going to be that the GRP has already been tapped to take the M5 helicoils ..... but as these seem to be falling through I think that the GRP threads will be somewhat stripped so I suspect that I'm going to need fix the helicoil somehow.

I can't drill out to M6 and re-tap as I need to use the current M5 bolts as they are the correct size for the fittings (it's the three louvres which fit right across the front windows). I could drill out the louvres and enlarge the countersinks to take M6 but that's getting a bit involved so I'm trying to avoid it.

Richard
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Stick with the plan Richard. If the epoxy gets squeezed out it wasn't needed, no loss. If it stays in, it was needed and it's where it needs to be.

Finding it hard to picture the tap going down the inside of the helicoil removing the epoxy on the outside of the helicoil :confused:
 
RichardS said:
I think that the problem is going to be that the GRP has already been tapped to take the M5 helicoils ..... but as these seem to be falling through I think that the GRP threads will be somewhat stripped so I suspect that I'm going to need fix the helicoil somehow.

I can't drill out to M6 and re-tap as I need to use the current M5 bolts as they are the correct size for the fittings (it's the three louvres which fit right across the front windows). I could drill out the louvres and enlarge the countersinks to take M6 but that's getting a bit involved so I'm trying to avoid it.

Richard
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Try these, no special tools required, designed for the problem you have.

https://www.tappex.co.uk/trisert-3-...ead=m5&length=10&material=316-stainless-steel

I always find tappex more than helpful, although they may well want to sell you far more than you need, it is worth talking to them.

if the recoil thread is already an issue, adding a new wire insert won't help I'm afraid
 
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prof pat pending said:
Try these, no special tools required, designed for the problem you have.

https://www.tappex.co.uk/trisert-3-...ead=m5&length=10&material=316-stainless-steel

I always find tappex more than helpful, although they may well want to sell you far more than you need, it is worth talking to them.

if the recoil thread is already an issue, adding a new wire insert won't help I'm afraid
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Thanks Prof ... I must say that I like the look of those inserts, sort of like a beefed-up helicoil on steroids. I could easily epoxy those inserts in, if necessary, without worrying about getting epoxy on the inner thread. Armed with the knowledge that I have alternatives, I'll have a go at removing the M5 bolts.

Coincidentally, Tappex are very close to where I live so I'll call in and speak to them.

Richard
 
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No problem :)

Drilling the correct size hole is quite important, but going slightly oversize and adding a light smear of epoxy has worked well for me in the past.

If they won't sell you a small quantity, ask them if they can point you in the direction of a customer who can.
 
RichardS said:
Thanks Prof ... I must say that I like the look of those inserts, sort of like a beefed-up helicoil on steroids. I could easily epoxy those inserts in, if necessary, without worrying about getting epoxy on the inner thread. Armed with the knowledge that I have alternatives, I'll have a go at removing the M5 bolts.

Coincidentally, Tappex are very close to where I live so I'll call in and speak to them.

Richard
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prof pat pending said:
No problem :)

Drilling the correct size hole is quite important, but going slightly oversize and adding a light smear of epoxy has worked well for me in the past.

If they won't sell you a small quantity, ask them if they can point you in the direction of a customer who can.
Click to expand...

Just as a follow-up to this thread, I called in at Tappex HQ in Stratford a couple of days ago and an very helpful engineer discussed my GRP insert issue and agreed that helicoils are not the best solution for bolting into this substrate. He gave me an M8 stainless steel insert which is clearly a far better solution. The insert is self-tapping and he reckons that provided I drill the hole to the correct size the insert will cut a very strong thread into GRP which will not need any epoxy .... but, as the Prof says, you do need to get the right size.

IMG_5507.JPG


Helicoil is top and Tappex is centre. The M8 bolt is not actually the type which secure my louvres but I just took it along as it's the same size.

The engineer says that there is a minimum order size of £30 but I would need a dozen inserts so that would be around that value anyway.

Richard
 
As my own update to this thread, it turned out that inside the engine bed was an embedded stainless plate that the bolts screwed into.

Apperently the old Volvo saildives are notorious for stripped threads when replacing the gaskets.
Any who, I went with Heli-Coil, worked perfectly.

IMG_0365.jpgIMG_0367.jpgIMG_0368.jpg
 
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