Repairing threaded hole in saildrive bed.

Ceirwan

Ceirwan

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I've got the engine out for a bit of a refurbish. (VP2001)

And I noticed whilst removing it that the circled bolt won't hold any tension, I'm assuming that the threads in the GRP base are simply cut into the fibreglass without there being any kind of steel plate inside. (If that was the case I probably wouldn't have the issue.

I'm thinking of three ways to fix it.

The first would be to drill the hole out a little larger and then fill with thickened epoxy before redrilling and tapping the thread again. The downside potentially to this one is that there seems to be a lot of space under the hole, I don't want to be filling forever.

The second is to wax up the bolt that goes in the hole so that epoxy won't stick to it, then reinstall it with thickened epoxy. When the epoxy cures, in theory I should be able to remove the bolt.

The third is to drill the hole out larger and then install a heli-coil again using epoxy.

Can anyone advise as to what the strongest solution would be?
IMG_0034.jpg
 
Buy a 'helicoil' kit. I would not bother with epoxy, maybe a dab of Loctite.

Post shoot from the hip edit:

Sorry I may have misunderstood is there no aluminium or steel glassed into the bearers?
 
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The second is one that is recommended by West for this type of repair. Assumes you have enough thickness of GRP for enough threads to hold.
 
Hi Norman, its not very obvious if there is or isn't as the hole has 30 years of gunk in it! Didn't get a chance to clean it at the time as I was busy removing the engine.

I feel like it should have steel glassed into the bearers, but its a Volvo saildrive bed that comes pre-made and I'm not sure if they do or don't.

Tranona, I'll check out their website, thanks for the heads up.

Prof, I believe the bolts are 10mm.
 
You should be able to detect the embedded steel ring by drilling a small diameter hole between two boltholes. Not sure helicoil will work well if the plate is too thin. Maybe open it up and epoxy a nut underneath the plate, repair in epoxy with a lightly greased bolt inserted to debond from the epoxy?
 
If it hasn't already got them, I would open up the grp beds and put steel strips inside with tapped holes for the bolts. Then make good with glass cloth and epoxy.
 
Thanks for the ideas. I'll do some more investigating to see for definite if there's a plate buried in there.
 
Ceirwan said:
Hi Norman, its not very obvious if there is or isn't as the hole has 30 years of gunk in it! Didn't get a chance to clean it at the time as I was busy removing the engine.

I feel like it should have steel glassed into the bearers, but its a Volvo saildrive bed that comes pre-made and I'm not sure if they do or don't.

Tranona, I'll check out their website, thanks for the heads up.

Prof, I believe the bolts are 10mm.
Click to expand...

Ceirwan...

I just so happen to have a never used Volvo Saildrive bed here and have just checked the thread arrangements:

There are a number of small plates, approx 30mm long by 20mm width, glassed in, sandwiched... these have then been tapped, so I'm guessing you could drill out and helicoil fairly easily.

HTH
 
stevie69p said:
Ceirwan...

I just so happen to have a never used Volvo Saildrive bed here and have just checked the thread arrangements:

There are a number of small plates, approx 30mm long by 20mm width, glassed in, sandwiched... these have then been tapped, so I'm guessing you could drill out and helicoil fairly easily.

HTH
Click to expand...

If the plates are quite thin, maybe drilling the hole out and inserting a rivnut or similar is a straightforward answer.
The plate will spread the load nicely.
Helicoil is a proper jo, but needs a reasonably thick lump of metal to work in, and if the hole is not blind, the bolt can wind the insert out of the bottom. Been there!

What size are we talking?
 
The fibreglass thickness is 14mm give or take, so plate thickness around 5 or 6mm. The hole isn't blind. Possible alternative might be to drill to next size bolt thread, and re-tap to suit?
 
stevie69p said:
The fibreglass thickness is 14mm give or take, so plate thickness around 5 or 6mm. The hole isn't blind. Possible alternative might be to drill to next size bolt thread, and re-tap to suit?
Click to expand...

If that's the case for the OP, an insert is the best solution, with some Loctite. Even if it doesn't go through the metal plate it'll never pull out of 14mm thick GRP.
 
Thanks Stevie.

I'll go the heli-coil route and install it with Red-Loctite, which should hold it in place in anything short of an engine fire!
 
NormanB said:
When you wind the helicoil in, it is designed so that, when the driving tang shears sufficient torque has been applied so that it will not 'unscrew'.
Click to expand...

Will it sheer if the hole is not a blind hole?
Or does the helicoil have a tapered thread that locks once its in?

I won't bother loctiting the actual engine mount bolt in, its not really needed, the only reason I would use it on the helicoil would be to stop it winding through when I put the bolt in, but I won't even put it on that if its not necessary.
 
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