I resealed my motor mount bolts the other day. Only had a couple drops of water in one hole.
Has anyone ever considered or tried some kind of metal sleeve either epoxied or sealed with 3M 5200 in the transom holes? I'm thinking maybe some aluminum tubing.

It just seems stupid to me that the boat builders would leave one of the most important structural points so vulnerable to water intrusion.

They just went composite on the transoms.

a bolt has to have some kind of compression to it to allow proper torque. with a sleeve in the
transom.. your only compressing the bolt to the sleeve.. with the weight of these engines.. that
sleeve would start moving around and cause bigger issues.

alot of boat mfg'ers don't use good sealant either. it saves them money not to use 3m 4200 or 5200

what steve said . if you really want to seal that wood thru the bolt holes, use the slow set epoxy reduced to a water consistency with; acetone for deep penetration in the wood, or lacquer thinner for medium penetration, or denatured alcohol for a little surface build up. tape off accordingly and use an art paint brush to apply and cure for at least 48 hours, i usually cure it 5 to 7 days but that's just a me thang. then you can use a silicon sealant when reinstalling the bolts. for this, i would most likely use the acetone for max penetration in the wood

Right idea, but wrong application of physics...torque is bolt stretch, not compression of the substrate.

Its composite. Not sure what it's a composite of but it looks pretty porous under the top cap and in the holes. Looks like it could absorb and hold some water for sure. I've always checked the bolts about every six months and they're always a little loose. Hopefully they stay tight a little better now because I sealed the heck out of the holes, bolts and the top cap. A lot better than it was anyway.

A sleeve would definitely have to be flush with the outside surface for a good mount.

All the torque would have to be bearing on the motor and on the plate or washers on the inside. Any compression would be at the transom. If I understand correctly.

i was thinking a wood transom, on a composite, i would reduce the epoxy with denatured alcohol, it wont melt styrofoam and will fill the pores better. of course you can do what you want but i will say not to use sleeves because it will eventually waller out those holes and damage your transom

A sleeve is used all the time in through fittings. The secret is to use a metal, plastic, or composite that is malleable enough to crush when torque is applied.

If your transom is compressing enough that you can see it when torque is applied to the transom bolts, a thorough inspection of your transoms substrate for defects or contamination is warranted.

then every transom out there is bad.. cause i've seen compression on every one of them.

composite doesn't mean it's not compressable. it just means it's a man made material that won't rot.

torque is torque, bolt stretch or compression or even opening a car door is a result of using torque, can you have torque without bolt stretch, why yes you can.

sleeves, crush sleeves, yeah they are used in a lot of places. would i expand an existing hole to insert a sleeve on the engine mount to transom on a boat, no way. would i use a crush sleeve on an existing hole that has already been damaged and wallered out, possibly but depends on the situation

Yep...It would be crazy to drill out the transom holes except as a last resort and even crazier to use smaller bolts but I would still rather have those bolts sitting on something more solid that could be sealed up better.

Oh well... back to the boat builders.