Transom plate sealant question

[Bwallis362]

So I finally pulled the trigger on a used CMC power tilt and trim for the Jon boat. Before taking the old motor off, I saw that the outside portion of the transom had an 1/8” thick aluminum plate attached, that the motor had mounted to. Unfortunately the size of the plate was just a little shorter in length than the mounting holes for the CMC trim mount. Therefore, my plan was to detach the old plate and replace it with a longer plate that would expand the full size of the cmc unit to allow flush mounting to the transom. After removing the motor I began to try and chisel off the old plate and unfortunately after working the plate a bit, my fears were confirmed as it became apparent that it had previously been welded in place and after getting some of the top portion off, I could even see some areas of light down inside the back of the boat. I have now changed my plans and am thinking it best to stop trying to remove the plate (I don’t want to get in too much of a project and don’t have the skills/ knowledge for an extensive transom repair.) Instead, I’m thinking I will drill some new holes for the top mounting portion of the CMC unit (the lower ones actually fit within the limits of the current transom plate. This would mean that a small area of the outside edges of the CMC device would overhang outside the limits of the current transom plate, but I would be able to get most of it to lie flush on the plate. My questions are 1) is there enough concern with doing it this way to make it necessary to go another route?
2) if it is necessary to go another route, what do you recommend?
3) what product do y’all recommend to reseal and fill the gap I made in the top portion of the transom plate? Thanks for the help! I will try and include some pics. I made a template of the CMC portion that mounts to the boat so you can see where it overlaps with the transom plate and can see how the mounting holes on top are spaced too far to fit the plate. View attachment IMG_3529.jpegView attachment IMG_3528.jpegView attachment IMG_3533.jpeg

 

[Bwallis362]

So I finally pulled the trigger on a used CMC power tilt and trim for the Jon boat. Before taking the old motor off, I saw that the outside portion of the transom had an 1/8” thick aluminum plate attached, that the motor had mounted to. Unfortunately the size of the plate was just a little shorter in length than the mounting holes for the CMC trim mount. Therefore, my plan was to detach the old plate and replace it with a longer plate that would expand the full size of the cmc unit to allow flush mounting to the transom. After removing the motor I began to try and chisel off the old plate and unfortunately after working the plate a bit, my fears were confirmed as it became apparent that it had previously been welded in place and after getting some of the top portion off, I could even see some areas of light down inside the back of the boat. I have now changed my plans and am thinking it best to stop trying to remove the plate (I don’t want to get in too much of a project and don’t have the skills/ knowledge for an extensive transom repair.) Instead, I’m thinking I will drill some new holes for the top mounting portion of the CMC unit (the lower ones actually fit within the limits of the current transom plate. This would mean that a small area of the outside edges of the CMC device would overhang outside the limits of the current transom plate, but I would be able to get most of it to lie flush on the plate. My questions are 1) is there enough concern with doing it this way to make it necessary to go another route?
2) if it is necessary to go another route, what do you recommend?
3) what product do y’all recommend to reseal and fill the gap I made in the top portion of the transom plate? Thanks for the help! I will try and include some pics. I made a template of the CMC portion that mounts to the boat so you can see where it overlaps with the transom plate and can see how the mounting holes on top are spaced too far to fit the plate. View attachment 403221View attachment 403222View attachment 403223

What I’m leaning toward doing is getting everything ready to mount (including drilling the new hole locations in the CMC plate and transom, but before tightening the bolts I would push as much marine Tex into the crack I created then tighten everything and surround the outside edges of the transom plate with more marine Tex. Y’all think that would work?

 

[mr 88]

Usually when metal plates are added the transom itself is rotted out . This would be the first thing I would verify ,one way or another . As far as sealant goes , 3m4200 is what I would use . It's the same as the 5200 except not permanent.

 

[Scott Danforth]

The aluminum plate is a bandaid as stated above. I personally lean towards Sika products or lifecaulk vs 3M lately

 

[Bwallis362]

So on the inside of the transom there are metal plates on top and below them is a pretty large gap before the bottom inside of the boat. To verify, I dug between that gap with a long thin rod a little and the pictures show that the wood between is definitely rotted. The space below the plates is so small there’s no way I could replace the wood without taking everything apart. What’s worse is that many of the obstacles in the way of getting these plates off are riveted into the hull of the boat. That’s something I definitely don’t want to have to deal with if I don’t absolutely have to. Any other possible suggestions would be greatly appreciated. The boat was doing fine as it was, I just really wanted power t/t but wouldn’t have messed with anything if I’d known what I might’ve been in for. Thanks for the help and knowledge! Looks like y’all were right on the wood rot.View attachment IMG_3539.jpeg

 

[Scott Danforth]

Weekend job. I recommend doing it correctly

 

[Bwallis362]

That’s what I figured