1999 Seaward s25 yanmar 1gm10 loose /stripped motor mount bolt repair

Oct 3, 2021
18
Seward S25 Oahu
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My son's boat is in Oahu. He is on deployment but we will both be there on 10/14
I'm getting parts together to replace the dripless seal cutlass bearing and repair the bolt holes.
We will be lifting or pulling this tiny little guy to do the work.
I was told by Hake that there is no wood in the stringers. It actually looks to me that it's just part of the larger hull liner/tub.
I imagine it's just a thick layup in the part below the motor mounts.

I'm looking for confirmation from anyone who knows this boat along with brainstorming on the best way to fix it.
Thanks

My first post! Be kind
 

Tedd

.
Jul 25, 2013
464
Between Boats near Vancouver, BC
Hi @Williammiller100 ,

I'm unclear which threads are stripped. Is it one of the screws that attach the mounting plates to the hull fiberglass?
 
Nov 6, 2006
9,225
Hunter 34 Mandeville Louisiana
An option: use a piece of flat 1/4" plate (steel or aluminum or stainless) same width as the mount's foot plate and 2-4" longer . Drill the plate and tap it for bolts thru the mount. drill the plate for those lag bolts at the ends of the plate overhang. Line up the tapped holes with the old stripped holes in the glass .. for extra security in that mount, you could epoxy it to the fiberglass ... but probably not necessary. Re-align the engine..
 
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Tedd

.
Jul 25, 2013
464
Between Boats near Vancouver, BC
Given the general level of quality of Seawards, it wouldn't surprise me if there's an aluminum or stainless steel plate embedded in the fiberglass, with tapped holes, or possibly some kind of embedded fastener. If that's the case, I'd probably use Loctite Form-A-Thread. I've used that a lot in car racing applications and I'm very impressed with how easy it is to use and how strong and durable the resulting threads are.
 

Tedd

.
Jul 25, 2013
464
Between Boats near Vancouver, BC
Or redrill and retap for oversize bolt if there is a glassed-in (probably aluminium) plate.
It's definitely worth trying the thread repair, first, with over-sizing as a fall-back plan. And, if the threads are an embedded fastener instead of a tapped plate, then thread repair compound is the only practical way I can think of that allows the same hole to be used.
 
Oct 3, 2021
18
Seward S25 Oahu
I found a drawing of the yanmar motor mount. Diameter of the mounting hole is 12.2 (I assume metric)
On a seward Facebook group a member with an older (1994) boat found lag bolts. Another with a '96 s25 had 3/8 threaded bolts going into a backing plate in or below the fiberglass.

If we find that then we could easily drill and tap to 10mm, 7/16", or 12 mm. All are smaller than the holes in the mounts.
If we don't have a backing plate I was thinking of a deep rivet nut, or some other expanding wedge anchor.
Some of this depends on how deep the fiberglass layup is at those mounting locations.
 
Oct 3, 2021
18
Seward S25 Oahu
This is something we have in mind if we can't get the holes repaired. But what's the best faster for the application to screw the plate to the fibreglass
 

Tedd

.
Jul 25, 2013
464
Between Boats near Vancouver, BC
You might want to look into some of the threaded inserts that are designed to work with composite materials, such as these or these.
 
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RoyS

.
Jun 3, 2012
1,205
Hunter 33 Steamboat Wharf, Hull, MA
You may be able to rotate the motor mounts enough to drill new mounting holes.
 
Jan 27, 2008
3,008
ODay 35 Beaufort, NC
You should never have a structural fastener screwed directly into GRP (glass reinforced plastic). Think of the name, it is plastic. It has to have an insert or plate bonded in to the layup to have enough strength for that application. If it is a plate you can tap it larger and install a self locking helical coil insert. If it's aluminum use some zinc chromate primer in the hole or on the insert to prevent galvanic corrosion. Those stringers are likely hollow and if you check with the manufacturer you may be able to cut an access port using an oscillating tool and then use a bolt with a washer and locknut. My stringers have access ports like that.
 
Oct 3, 2021
18
Seward S25 Oahu
You should never have a structural fastener screwed directly into GRP (glass reinforced plastic). Think of the name, it is plastic. It has to have an insert or plate bonded in to the layup to have enough strength for that application. If it is a plate you can tap it larger and install a self locking helical coil insert. If it's aluminum use some zinc chromate primer in the hole or on the insert to prevent galvanic corrosion. Those stringers are likely hollow and if you check with the manufacturer you may be able to cut an access port using an oscillating tool and then use a bolt with a washer and locknut. My stringers have access ports like that.
Chris made it back. He's going to pull a few of the bolts and survey what he can.
Thanks All
 
Oct 3, 2021
18
Seward S25 Oahu
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This is all that was holding the motor mounts to the stringer.
Backed out with his fingers.
Not much holding that crazy motor in place.

Heading to Oahu in the morning!
 

NYSail

.
Jan 6, 2006
2,735
Beneteau 423 Mt. Sinai, NY
My stringers which are similar have access holes next to each mount so I can get in there and hold the nut. I would assume those are hollow. Get a larger hole saw for your drill.
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Oct 3, 2021
18
Seward S25 Oahu
Turned out to be a simple fix because we removed the motor to pull the shaft, replace the dripless and cutlass bearing.
The original bolts were only 5/16.
Two holes were stripped. The ones circled.
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Found aluminum backing plates. Drilled and tapped all the holes to 7/16