Thru Transom Exhaust Block Off Plate - Sealant/Adhesive?

[StevNimrod]

I have a 1994 Wellcraft Excel with a thru the transom exhaust system made by Stainless Marine. Save the comments on loud pipes - it was like this when I got it (not that I'm saying it's a bad thing either).

While I'm in the process of painting the bilge (engine swap so why not) I figured I'd track down a small leak I was having last season. It appears the block off plate was not sealed correctly and had a slight leak. I have a new style plate and the seal for it as well as a full complement of Merc manuals. The manual (which I don't have in front of me) states that the procedure is to simply install the seal and plate, then torque the screws to 23 ft-lbs (or whatever it was).

My question, to those of you with this setup who may have done this before: should I use any type of sealant or adhesive when installing this? The guy at the Merc dealer's parts counter suggested bellows adhesive, my marine mechanic suggested 5200 or Life Seal, and I also have some Quicksilver Perfect Seal laying around. Once I get the new motor in I won't have access to the plate so I'd like to get it right the first time. I don't want to install it without any sealant and have it leak, and I don't want to install it with sealant only to have it leak as well.

Sorry for the novel fellas. Thoughts?

 

[Zackman]

Re: Thru Transom Exhaust Block Off Plate - Sealant/Adhesive?

I too struggled with this same question when I resealed my y-pipe (same seal and sealing surface as your block off plate). I ended up using bellows adhesive and it is working fine. My next choice would have been perfect seal.

The 5200 will seal it, but if you ever need to take it off it will be near impossible. 3M does make 4200, which has about 1/2 the holding strength as the 5200 is made to be removed if needed and will be plenty strong enough for this applicaiton.​

 

[StevNimrod]

Re: Thru Transom Exhaust Block Off Plate - Sealant/Adhesive?

I too struggled with this same question when I resealed my y-pipe (same seal and sealing surface as your block off plate). I ended up using bellows adhesive and it is working fine. My next choice would have been perfect seal.

The 5200 will seal it, but if you ever need to take it off it will be near impossible. 3M does make 4200, which has about 1/2 the holding strength as the 5200 is made to be removed if needed and will be plenty strong enough for this applicaiton.​

Zackman,

Thanks for the vote of confidence on the bellows adhesive. How long has yours been in service with the bellows adhesive?

I have 5200 on it now -- I originally planned on reusing the old block off plate (which was the older style, three times as thick as the newer one) but there was a bit of pitting and I decided to give myself one less thing to worry about and get the newer version. It should be interesting getting the 5200 out tomorrow, between coats of bilge paint.

 

[Zackman]

Re: Thru Transom Exhaust Block Off Plate - Sealant/Adhesive?

3 months and about 15 hours...

You have 5200 on it now and it was leaking?

Good luck getting the plate off. I've heard they make a solvent to help loosen the 5200. I've seen it at West Marine, but can't remember the name.​

 

[StevNimrod]

Re: Thru Transom Exhaust Block Off Plate - Sealant/Adhesive?

3 months and about 15 hours...

You have 5200 on it now and it was leaking?

Good luck getting the plate off. I've heard they make a solvent to help loosen the 5200. I've seen it at West Marine, but can't remember the name.​

Yes, I have 5200 on it now. No, it is not leaking. That is probably because the boat is on land waiting for me to finish bilge painting and engine installation.

The whole engine installation was originally going to be simple and straightforward. Since I was trying to work fast, I went the 5200 route using the old style block of plate that was previously installed. Then I found a few areas in the bilge that needed some serious attention. While I was at it, I decided that painting the bilge wasn't a bad idea so I decided to pump the brakes on my urge to get in the water quickly and go through everything I had easy access to (like replacing a perfectly functional bilge pump and other stuff that would be nightmarish to do with a motor installed). That got me to thinking that I should get a new block off plate and get a few more votes on how to install it.

For whatever reason I've never had any problem getting stuff apart that's been adhered/sealed with 5200. Then again, I like to use a 8 lb. hammer to drive thumb tacks so finesse isn't my strong point.

Edit: I think what you were trying to get at is what was on it when it leaked. It appeared that the previous owner installed the plate with some type of clear silicone. Like what you would get from HD to caulk a bathtub. It was pretty much cracked to bits when I pulled it off. Then I did the install with 5200 (in a rush). Now I have time and want other opinions.

 

[wca_tim]

Re: Thru Transom Exhaust Block Off Plate - Sealant/Adhesive?

I wound up making a plate out of relatively thick aluminum stock and it's on there with locktite in the threads and a bead of 5200... I'm sure i could get it off if i had to.. but why in the work would I ever think about putting the y-pipe back???

 

[StevNimrod]

Re: Thru Transom Exhaust Block Off Plate - Sealant/Adhesive?

I wound up making a plate out of relatively thick aluminum stock and it's on there with locktite in the threads and a bead of 5200... I'm sure i could get it off if i had to.. but why in the work would I ever think about putting the y-pipe back???

I have something similar - apparently the "old style" Merc plate is relatively thick. Maybe I'm being paranoid, but it would not be cool to put the motor in only to find I still have a leak.

What was your reasoning behind fabricating your own plate rather than getting one from Merc? Just out of curiosity.

 

[wca_tim]

Re: Thru Transom Exhaust Block Off Plate - Sealant/Adhesive?

I had some spare ca. 3/8 aluminum plate, a bandsaw and a drill press....