I was hoping someone could give me some direction on this. I have read a few websites and find a bunch of different answer. I am replacing a 1980 Johnson 175 hp with a 2001 Yamaha Max 150 (on a 1995 Nitro). I need to fill the old holes and redrill new ones. How do I go about filling the old holes already in the transom. Any help is greatly appreciated. Thanks. -Jim

I would insert and wooden dowel covered in silicone or 3m 5200. Then I would use fiberglass resin over it on the outside and inside.

or you could also pack it in there with some cat hair and glass over the whole lot.

   Heres what I did...I found a local boat mechanic looking for side work. He is charging me $245 to remove the old motor, fill the holes, place new motor on, hook up all lines, wires, control box, and gauges.....I thought that was a pretty good deal.....well that was easy!

Heres what I did...I found a local boat mechanic looking for side work. He is charging me $245 to remove the old motor, fill the holes, place new motor on, hook up all lines, wires, control box, and gauges.....I thought that was a pretty good deal.....well that was easy!

That was easy. Fair price as well.

I was hoping someone could give me some direction on this. I have read a few websites and find a bunch of different answer. I am replacing a 1980 Johnson 175 hp with a 2001 Yamaha Max 150 (on a 1995 Nitro). I need to fill the old holes and redrill new ones. How do I go about filling the old holes already in the transom. Any help is greatly appreciated. Thanks. -Jim

For future reference and to all who want to plug a hole in a transom or deck.  

If the hole is perfectly round, and for the sake of discussion, the transom thickness, not counting the fiberglass is an inch and a half thick, enlarge the holes to a depth of 1/2 inch on each side.  

Again, for the sake of illustration, make the outer holes larger by at least one inch in diameter.

This will provide a step on each side.  Make three 1/2 inch plywood discs, one the size of the small hole, and two the size of the larger holes.  

Then you can epoxy and clamp the assembly together.  It will then be structurally sound.  Bevel the glass around the edges of the patch for a couple of inches.  Clean with acetone, then apply glass to the original thickness or slightly thicker.

When it sets up, level the patch with a belt sander,  then smooth with a sanding block or a hand sander and 120 grit paper.  Any small voids or low areas can be filled with bondo, followed by sanding.

Prime, paint, and forget about it.

or if you just want to stop the water, stuff 4-5 Senkos in there... :-X ;D

I just put bolts in the hole and sealed it with silicone.

I just put bolts in the hole and sealed it with silicone.

That is a practical and easy way to solve your problem.  Just make sure the silicone holds and doesn't leak!  Did you degrease the area around the holes first?

I bought a junk boat just to get the motor.  The reason it was a junk was the motor mounting holes were not sealed good and the transom got wet and rotted.  I liked the solution above that used the plywood discs laminated in the holes.  More work, but you won't have to wonder about your transom.  Also, make sure you use a good product to seal the holes for the new motor as well.