Replace Engine mount bolts?

[Condor1970]

Well, I gave this a shot and it didn't work. I had some stripped out threading in the front engine mount wood block, where the engine mount bolts to the hull, on my 89' Regal. I managed to dry the wood, and I tried to fill the holes with epoxy, and rethread them using the original lag bolts that were used before. However, the vibration just pulled them loose again.

I did notice there is a few inches gap beneath the wood block and the hull/bilge. I think I could just drill those holes out all the way through to the bilge, and replace the Lag bolts with some very long stainless bolts of the same diameter, with some large fender washers on the bottom, and just use a nut to bolt them on, instead of the original lag bolts.

Has anyone had to do this before?

 

[Mud Puppy]

Probably the best thing would be to replace the block. From an Engineers point of view, bolts are always better if you can get 1-1/2 threads showing out of the nut and a poly lock would be better still. Bet the original lag bolts were only zink alloy steel anyway, but you know how many thousands of boats out there are just that way and have been for years.

Real lumber yards (not sure of the supper stores since I don't use them) have round closet rod millwork and you could bore out your block and try epoxying or gluing in a "plug". Any good quality mastic should do the trick as long as it is exterior grade or you seal it. I'd go 1/8" - 3/16" larger so the bond isn't starved.

We use to scarf rafters and only used LN and a few 16d nails or 3" wood screws on a 2x6 scarfed 36" and would support a roof deck and shingles.
Stress is gonna be tensile on the port side and compressive on the starboard side, shouldn't be any shear at all on the mounting block

Some pics might help get you a fix that will work for you.

 

[Woodonglass]

If the MM's are rotten, what else is? Have you core samples the transom to ensure it's not going bad? If it is it can effect the outdrive alignment and mess things up there as well. Rotten Stringers can/will compromise the structural integrity of the hull. I agree with MP that you should attempt the rebuild the MM.

 

[sheboyganjohn]

Personally I see no problem with thru bolting the motor mounts and actually see it as the superior method. There is no way I am putting lag bolts back in my Sea Ray, that is going to be thru bolted. I have to agree that you need to check and make sure there is not a rot problem.

 

[tpenfield]

Got any pictures to share?

 

[jigngrub]

Sounds rotten to me.

If you're going to try to through bolt it, I'd use cut or plate washers instead of fender washers.

 

[Condor1970]

When I was cleaning out the holes for thel ag bolts before I tried using epoxy to fill and tap them, I did notice the threading pieces that I picked out were rotten. However, the sides of the holes, and when I drilled down a little further for the epoxy, I got fresh wood out. That's why I'm thinking some moisture must have gotten into the lag bolt holes, and rotted the threading, but not enough to really rot out the whole mounting block.

 

[Rickmerrill]

I'm really hoping I'm wrong for your sake but there is a saying around here that "rot starts from the bottom up and the rear forward". Without a picture we're all guessing but I am skeptical about the idea that water got in around the top of the lag bolt and caused it to only rot around the threads. Water just doesn't see the top of the engine supports except from a hose when cleaning. Moisture/wet wood is the most probable reason the epoxy didn't stick to the wood. If it did stick it would have pulled out a good bit of good dry wood along with the epoxy. Is that what happened?

 

[jigngrub]

When I was cleaning out the holes for thel ag bolts before I tried using epoxy to fill and tap them, I did notice the threading pieces that I picked out were rotten. However, the sides of the holes, and when I drilled down a little further for the epoxy, I got fresh wood out. That's why I'm thinking some moisture must have gotten into the lag bolt holes, and rotted the threading, but not enough to really rot out the whole mounting block.

Fiberglass encapsulated wood doesn't dry out once it has become wet, especially in the deep, dark, damp recesses of an engine well or below deck. And epoxy isn't going to penetrate or bond to wet/damp wood.

If you're not going to replace the mount block, your next best option is to through bolt and wait for the mount block to rot out completely.

 

[tpenfield]

I am sure that many boat manufacturers still use lag bolting to save a few bucks, but they have a limited life span. When you rebuild your engine mounts, which I believe you will have to, go for a thru-bolted arrangement.

 

[Fastatv]

Well, I gave this a shot and it didn't work. I had some stripped out threading in the front engine mount wood block, where the engine mount bolts to the hull, on my 89' Regal. I managed to dry the wood, and I tried to fill the holes with epoxy, and rethread them using the original lag bolts that were used before. However, the vibration just pulled them loose again.

I did notice there is a few inches gap beneath the wood block and the hull/bilge. I think I could just drill those holes out all the way through to the bilge, and replace the Lag bolts with some very long stainless bolts of the same diameter, with some large fender washers on the bottom, and just use a nut to bolt them on, instead of the original lag bolts.

Has anyone had to do this before?

I'm curious as to which engine you have....3.0L maybe?