Leaking bolts jackplate to transom...

[Johnnyred]

My bilge was staying so dry that I had cobwebs in it. Then I checked the torque on the jackplate to transom bolts to make sure I had 55ftlbs... because you're supposed to right. Not thinking about not letting the bolts move during this process, I obviously damaged the sealant's waterproof gasket and got leaks. I tried removing, replacing the bottom 2 bolts one at a time without removing the jackplate. I used lots of sealant on the bolt shanks like the Merc manual says. I had a nice squished out mass of sealant around the inside 1.5" washer.

Well, this made it worse and the amount of water coming in is more than I care to have.

I had a local shop install my manual plate originally and had the same kind of leaks. I ended up going 1.5hrs away to my dealer who completely removed and re-sealed the plate and however they did it worked 100%.

I have the required motor lift ring and base and can easily and cheaply rent an engine hoist as I have done that before with a jackplate to motor project.

If I try to remove the jackplate, clean all the old sealant off, and re-mount, re-seal the bolts myself, what else other than liberal application of sealant to the bolt shanks is required? I wouldn't mind doing the project myself but want to get it right. Since the places in the jackplate where the bolts pass through are slots, I don't see how I can create a gasket with sealant on the outside as there is nothing that is tightly "sandwiched" against the outside of the transom bolt hole.

Big thanks in advance for any advice from those in the know!

[Skeet'r89]

What kind of sealant have you been using?

[McQuaig]

I've never seen a jackplate with "slots" for the mounting bolts on transom side. Do you have a pic of it?

[Johnnyred]

attached

[McQuaig]

I may be way off, but is it possible your plate is installed backwards? I had one of these years ago and I'm pretty sure mine had the slots on engine side. That made it easy to change engine mount by only loosening the bottom bolts and removing top ones to remount. Also, that would mean the larger face of jackplate would better spread the weight/pressure over the transom. However, if I'm wrong, it also looks like the trim at top of your transom is preventing the inner plate from fitting solidly to transom...

[Johnnyred]

I may be way off, but is it possible your plate is installed backwards? I had one of these years ago and I'm pretty sure mine had the slots on engine side. That made it easy to change engine mount by only loosening the bottom bolts and removing top ones to remount. Also, that would mean the larger face of jackplate would better spread the weight/pressure over the transom. However, if I'm wrong, it also looks like the trim at top of your transom is preventing the inner plate from fitting solidly to transom...

Bob, I had the same thought about the plate being installed backwards. I found the installation manual and it looks like my installation orientation is indeed correct. Just to be sure I have reached out to TH Marine who manufactures and sells the CMC plates to confirm.

There is a plastic "plate" between the transom and jackplate that levels the mounting surface, compensating for the top trim. It is black in color and your can see part of it in one of the pictures I posted. It is a standard item used with jackplates to level mounting surfaces, was installed by the dealer. All my aluminum boats with plates have used a plastic piece like this.

[bass-action]

Don`t really like that slot. I would do a complete ring of silicone around each bolt hole the shape of the slot, then very liberal on the bolt washers on the inside of transom. Then completely fill the slots with silicone,hopefully quick enough before the other silicone starts to set up.

[Johnnyred]

Don`t really like that slot. I would do a complete ring of silicone around each bolt hole the shape of the slot, then very liberal on the bolt washers on the inside of transom. Then completely fill the slots with silicone,hopefully quick enough before the other silicone starts to set up.

In tried filling the slot but when replacing the bolts one at a time without removing the plate completely and because of the tight space inside the plate and limited visibility, I found that hard to do. I agree that filling the hole completely could help.

[Johnnyred]

I guess my problem and this discussion begs the questions:

- Shouldn't a proper sealant application on the inside of the transom bolts be enough to keep water from leaking into the bilge without any sealant application on the outside? Seems like it should even though I am trying to seal the outside too. My hull/transom is all aluminum no wood inside to worry about rotting

- Is it possible that while trying to torque the bolts to the 55ftlbs that Mercury specs for my motor that I am compromising the sealant application?

[Johnnyred]

Don`t really like that slot.

I prefer the slot to not be there either. I am starting to dislike it.

[McQuaig]

I guess my problem and this discussion begs the questions:

- Shouldn't a proper sealant application on the inside of the transom bolts be enough to keep water from leaking into the bilge without any sealant application on the outside? Seems like it should even though I am trying to seal the outside too. My hull/transom is all aluminum no wood inside to worry about rotting

- Is it possible that while trying to torque the bolts to the 55ftlbs that Mercury specs for my motor that I am compromising the sealant application?

Yes, seems to me like the way you're sealing it should work fine, especially if there's no wood in transom. Only other thing I can think of is water getting somewhere else? My brother's aluminum boat had enough flex at transom that the seam at the bottom, back of splashwell was opening up enough to let water in there...

[Johnnyred]

Pretty certain water is coming in at the mounting bolts. I had zero water leak until I tried to check torque on the mounting bolts and obviously disturbed the existing watertight seal. Like I shared, I had this before when a sloppy local dealer originally mounted my plate but my regular dealer re-mounted it and I had zero leaks. My Ranger's transom is heavily steel reinforced and handles the loads.

[billnorman1]

I'm watching this post. I installed my own jackplate with zero leaks. I'm going to go out and look at it now. Anyhow, if you're checking torque on a through bolt, always turn the nut not the bolt. If initially sealed correctly it should never leak.

[Johnnyred]

I'm watching this post. I installed my own jackplate with zero leaks. I'm going to go out and look at it now. Anyhow, if you're checking torque on a through bolt, always turn the nut not the bolt. If initially sealed correctly it should never leak.

Bill, thanks for checking in. What make/model jackplate did you install?

Yep, like a dummy I let the bolts spin when checking torque. Live and learn.

[Dixie-Raven]

Are you not using 4200 Sealant?

[Johnnyred]

I'm using Starbrite Marine Silicone Sealant, same as the dealer used when they installed with no leaks, same as jackplate manufacturer Vance recommends. It is rated for below the waterline use same as 4200 but it has somewhat lower adhesive properties than 4200. It still bonds strongly to metal surfaces which is my application. It is the clamping force of the bolt assembly that holds the motor on and adhesives are not needed. The sealant is there for gasketing and providing waterproofing that will last.

[191 champ]

If I'm understanding correctly, I would assume that the plastic plate would have a round hole. If so, apply sealant between the transom and the plastic plate with plenty squeezing out of the bolt hole. Because of the slot, it wouldn't help much seal between the plastic plate and the jack plate.

[Johnnyred]

If I'm understanding correctly, I would assume that the plastic plate would have a round hole. If so, apply sealant between the transom and the plastic plate with plenty squeezing out of the bolt hole. Because of the slot, it wouldn't help much seal between the plastic plate and the jack plate.

Yep I think you are spot on and that's what I intend to do

[willwork4fish]

Are you not using 4200 Sealant?

from the pic that's not 4200. Mounting a JP or engine is the one spot I always and only use 4200.

[Dixie-Raven]

from the pic that's not 4200. Mounting a JP or engine is the one spot I always and only use 4200.

Yes that's why I was asking.