Engine mount fixing point failure / repair

[icarusbop]

Hello:

I have a Benneteau Evasion, with a loose engine mount.
The engine mounts are bolted to epoxy coated wooden beams in the bottom of the hull, using 10mm coach bolts that bolt straight into the wood.
On the mount in question, the bolt will not tighten up because the thread in the wood has been stripped. I am trying to think of the best way of fixing this whilst removing as little of the wood as possible.
My best idea is to use a threaded insert, where I can drill the hole out to 12mm and screw the insert into the wood (probably with a little epoxy for extra strength), the centre of the insert has an M10 female thread, which will allow me to fix the engine mount with standard M10 bolts.
There are two potential issue with this solution:
1: The inserts only seem to be available in mild steel - how much of an issue is this, given the current engine mounts and bolts are also mild steel?
2: The longest I can find these inserts is 25mm, the original bolt threaded length is 50mm, potentially providing less strength - would this reduce the strength of the fixing by a significant amount?

Are there any other ideas or suggestions anyone can think of?

Thanks.

 

[Tranona]

Just drill the hole out and epoxy a piece of dowel into the hole then re-drill with the correct pilot drill for the 10mm coach screw. 12 or 15mm dowel and 8mm drill, but counterbore the top of the hole to take the 10mm shank.

 

[rob2]

Coachbolts, really? Straight into the wood? I'm not sure whether you originally had a threaded insert or the bolts were just wound into the wood. If you fit 25mm long inserts you won't lose a significant amount of strength, I believe. Many older installations used coachscrews straight into the bearers - the cosarser thread is better suited to gripping into wood.

Rob.

 

[GrahamM376]

Just drill the hole out and epoxy a piece of dowel into the hole then re-drill with the correct pilot drill for the 10mm coach screw. 12 or 15mm dowel and 8mm drill, but counterbore the top of the hole to take the 10mm shank.

+1 except I would use polyurethane adhesive, this product works fine on damp or even wet timber and foams to fill any gaps - http://www.wudcare.co.uk/fastgrab.htm

 

[icarusbop]

Coachbolts, really? Straight into the wood? I'm not sure whether you originally had a threaded insert or the bolts were just wound into the wood. If you fit 25mm long inserts you won't lose a significant amount of strength, I believe. Many older installations used coachscrews straight into the bearers - the cosarser thread is better suited to gripping into wood.
Rob.

Sorry, that was a typo, they are actually coach screws.

 

[icarusbop]

Just drill the hole out and epoxy a piece of dowel into the hole then re-drill with the correct pilot drill for the 10mm coach screw. 12 or 15mm dowel and 8mm drill, but counterbore the top of the hole to take the 10mm shank.

Hello, and thanks for the suggestion. This was my initial thought but I was not sure if the bonding would be strong enough.
However, after looking at the photos of my engine space, I'm not sure I will be able to get a drill in to do this work, I'll havr to have a close look at the area and report back.
Thanks

 

[LittleSister]

My best idea is to use a threaded insert, where I can drill the hole out to 12mm and screw the insert into the wood (probably with a little epoxy for extra strength), the centre of the insert has an M10 female thread, which will allow me to fix the engine mount with standard M10 bolts.
There are two potential issue with this solution:
1: The inserts only seem to be available in mild steel

M10 threaded inserts are readily avaiable in stainless steel (not marine grade, I think, but presumably far better than mild steel?).

 

[GrahamM376]

Hello, and thanks for the suggestion........ I'm not sure I will be able to get a drill in to do this work, I'll havr to have a close look at the area and report back.
Thanks

If you can't get a drill in, then shape a piece of wood to the size of the coach bolt, drill a pilot hole down it, drip some polyurethane glue in to the existing engine mount hole and hammer the plug in. Once set, it will be very strong.

 

[Scotty_Tradewind]

+1 except I would use polyurethane adhesive, this product works fine on damp or even wet timber and foams to fill any gaps - http://www.wudcare.co.uk/fastgrab.htm

polyurethane extremely good on clean timber with a very tight fit.... remember the filling aspect of foaming up in the air pockets etc.. has no strength.

S.

 

[Tranona]

Hello, and thanks for the suggestion. This was my initial thought but I was not sure if the bonding would be strong enough.
However, after looking at the photos of my engine space, I'm not sure I will be able to get a drill in to do this work, I'll havr to have a close look at the area and report back.
Thanks

You could just pour epoxy down the oversize hole, grease a screw, wind it in, then when the epoxy has set the screw will come out leaving an epoxy thread to take the screw when you re-attach the mount.

 

[charles_reed]

Just drill the hole out and epoxy a piece of dowel into the hole then re-drill with the correct pilot drill for the 10mm coach screw. 12 or 15mm dowel and 8mm drill, but counterbore the top of the hole to take the 10mm shank.

Now how traditional can you get, it's worked for 3000 years.
I didn't think Tranona was that old though:ambivalence:

 

[TamT]

Drill a 20mm hole low down through the bearer in line with the fixing. You can then fit a 10mm nut and washer in the hole and bolt the mounting to it.

Colin

 

[peteK]

As others have said,plug the hole,redrill and use longer coachscrewso that it bites in to new wood.

 

[vyv_cox]

Just looking for something else and found these http://www.fastenerdata.co.uk/products/more/metric-coarse-thread-insert-stainless-steel-din7965.html Only description is 'stainless steel' which could many any one of many compositions, but probably OK for the purpose. A2A4 do them also.

 

[icarusbop]

Thanks to everyone for their help, in the end, I plumped for slightly fatter, bolts, 10mm longer than the originals, they worked fine.
However, when that mount was fixed I needed to refit one of the other for the stern of the egngine, this one was even less accessibile than the first one I fixed.
For this fix, I got some a4 theaded bar and chopped to length and epoxied then into the holes that had torn loose. when the epoxy had set I ran a washer and nut down the bolt to fix the mount in place - this worked fine also.

Now my engine is nice and quiet, the knocking has gone.

 

[Scotty_Tradewind]

good to know..... interested to hear if all o.k. after a seasons work from the engine.... should be perfect from your work done

good luck

S.

 

[fisherman]

Someone must have had a similar problem with my boat in the past. They drilled a 1" dia hole through the engine bed below each foot, then used a piece of round bar with a thread tapped sideways in it. Been fine for the 23 years I've had it, big engine too, 6 cyl 135hp Ford, but of course not the knocking you get with a single or twin.

 

[Scotty_Tradewind]

yes more the vibration with smaller engines the better condition the engine mounts need to be I guess?

S.

 

[propnut]

fisherman

Someone must have had a similar problem with my boat in the past. They drilled a 1" dia hole through the engine bed below each foot, then used a piece of round bar with a thread tapped sideways in it. Been fine for the 23 years I've had it, big engine too, 6 cyl 135hp Ford, but of course not the knocking you get with a single or twin.


That was how I was taught to mount bigger engines.We used to keep old prop shafts for that purpose.Vertually bomb proof !

 

[Spirit of Glenans]

Someone must have had a similar problem with my boat in the past. They drilled a 1" dia hole through the engine bed below each foot, then used a piece of round bar with a thread tapped sideways in it. Been fine for the 23 years I've had it, big engine too, 6 cyl 135hp Ford, but of course not the knocking you get with a single or twin.

Obviously inspired by the fixings for flatpack wardrobes