Sheared-off Front Engine Mount Screws - Glassed in?

Hi All,

In removing my engine from the boat for a rebuild, I managed to shear off the heads of all four front engine mount bolts. I have a 5.0 VP GL engine in a 2001 Glastron 205GT.

I spent the better part of yesterday soaking them with the PSF/Acetone rust solution and attempting to extract them using a bolt-extractor set. No luck. At this point three of the four almost certainly need to be completely drilled out because I tried using the largest reasonable extractor size (probably 60% of the screw shank dia). The fourth screw is mostly untouched.

The reason I'm posting is because the front engine mounts appear to be threaded inserts retained mechanically by the fiberglass hull. That is to say that I don't believe the heli-coil-esque solution is applicable here. In attempting to extract one of the holes I got a little bit of wood coming up the hole when drilling, so I would guess that it's some sort of wood block/fiberglass composite sandwich. My inclination is that I'm going to need to completely drill out the threaded insert and bond in four replacements. I plan on trying to create a template off of what's currently left of the screws to try and re-locate the new inserts.

Does anyone have any experience with this? Any suggestions for inserts, bonding, hole prep?

Attached is pdf with a few slides of the holes

Re: Sheared-off Front Engine Mount Screws - Glassed in?

Turn the mount a little, drill new holes, and use lag bolts like most boats have.

Re: Sheared-off Front Engine Mount Screws - Glassed in?

Don S said:

Turn the mount a little, drill new holes, and use lag bolts like most boats have.

Click to expand...

Ayuh,... Agreed,...

Just rotate it the width of the bolt, 'n use lags like every boat I've ever worked on..

There's just No reason for thread inserts...

Re: Sheared-off Front Engine Mount Screws - Glassed in?

I see. So the lag bolts are threading directly into a wood block beneath the outer layer of fiberglass?

I figured that since the screws were (so) stuck, it had to have been a corroded metal-to-metal interface.

Recommendations on bolt size?

Thanks for chiming in....

Joe

Re: Sheared-off Front Engine Mount Screws - Glassed in?

3/8" will hold fine. Drill a 5/16" hole, and coat the bolt threads with 3M 5200.
Acts like a lubricant when installing, and seals the wood from any moisture intrusion.

Re: Sheared-off Front Engine Mount Screws - Glassed in?

Don S said:

3/8" will hold fine. Drill a 5/16" hole, and coat the bolt threads with 3M 5200.
Acts like a lubricant when installing, and seals the wood from any moisture intrusion.

Click to expand...

Ayuh,.... 3/8" is probably enough, but I think all those I've done were 1/2" bolts in 3/8" holes....

Yer broken 1s just maybe thread inserts, it's just that I've never seen such a thing...

Ditto sealin' 'em up on the way in too...

Re: Sheared-off Front Engine Mount Screws - Glassed in?

Alot of boat manufacturers boast about "no wood". Instead they use composite material (plastic) in places where wood used to be. Your stringers are most likely the plastic but the actual mounts are still good old fashion "pine". Not treated or anything!
Make sure the old holes are sealed before you drill new ones. Before you quess where the mounts are going to wind up. Drill a test hole with an 1/8" bit, see what you drilling into prior to big holes. And use the 5200 w/stainless steel lags. 3/8" is plenty.