Originally Posted by Delta 15
I've been told you can dribble some oil (e.g. motor oil) into the bolt holes and that will protect the transom against water intrusion. After doing another repair, I happened to have some extra penetrating epoxy mixed up so I smeared that inside the holes with a Q-tip for the same result.
I can't see how putting motor oil on plywood is going to do the plywood any favours.
What I've done to protect the transom at the bolt holes is this;
1. For each hole, get a pair of flanged brass nipples (from the plumbing section of Home Depot/Rona/wherever) with an internal diameter that matches the diameter of the bolts, and that have a length that is at least half of the thickness of the transom.
2. Carefully measure the thickness of the transom, then shave the length of the nipples down so that the total length of each nipple is 1/32" less than half the thickness of the transom.
3. If necessary, ream the nipples just enough so that the bolt can slide inside the nipples.
4. Mark the spots on the transom where the centers of the holes need to be.
5. Drill narrow (~ 1/8") pilot holes at those spots through the transom (***use a guide to ensure that the hole goes perpendicularly through the transom!!!)
6. Measure both the diameter and thickness of the flange of the nipple.
7. Drill a shallow impression of the same diameter & depth as the nipple flange at the surface of the pilot holes.
8. Drill through the previously made pilot holes with a bit that matches the outside diameter of the brass nipples.
9. Dab some 3M 5200 (permanent adhesive sealant) over the exterior of each nipple and tap the nipples into the holes on each side of the transom until the flanges sit flush to the transom. At this point, the 2 nipples in each hole should just about meet at the center of the transom hole (the gap between them should only be about 1/16").
You now have rust proof, fully sealed brass sleeves through the transom which you can slide the mounting bolts through countless times without any worry of damaging the transom. When you mount & dismount the motor, put a small amount of sealant (I like 3M 4200 for this) on the bolt to keep any water from coming through the sleeve.