View Full Version : Alpha Transom Assembly Large O Ring Seal Leaks

01-19-2011, 11:17 AM
On the F14, we have a slow leak . We have verified it is the large O Ring type gasket seal around the transom assembly that is leaking at the bottom. As you know, this seal fits in a groove and is about 1/2" cross section and about 9 inches in diameter if it was a circle. It fit good in the groove when I put it in...too good really as I was expecting more of it to "puff out" so as to make a good seal when compressed against the transom. I glued the seal in the groove but used NO sealant against the transom. I used an aftermarket, probably Sierra seal.

Right now I have the transom assembly pulled back about an inch. Enough to lay a good bead of sealant and button it back up. Should I have layed sealant on to begin with? Or are there larger cross section diameter seals available?

01-19-2011, 11:40 AM
First you will need to inspect the wood around it. if theirs any soft spots in the wood the transom wont seal..it may not leak sitting still but will leak under way due to the transom flexing..

yes some mfr do seal the transoms with 5200, all the ones i have seen dont apply it directly to the seal but to the inner edge of the transom..

01-19-2011, 01:23 PM
are you talking about the large flat o-ring seal for thr drive shaft bellows area???

01-19-2011, 04:33 PM
The transom wood is fine as it is new and I re-verified it is still fine even though it is only two years old at this point. And the transom is flat.

Yes, it is the large flat o-ring seal that fits in a groove up next to the transom. And it leaks standing still since we can fill up the back of the boat on the trailer and watch the water leak there. And when I pulled the transom assembly back, I could see a little dirt on it where water went past it. It is simply not a big enough cross section, in my opinion.

I seem to need a bigger cross section o-ring or use sealant to give me more rubber to seal with. I think it comes down to two choices, either the aftermarket seal I have is not large enough -- and maybe a genuine Mercury part is larger - or I need to add extra sealant.

I'm trying to get an idea if anyone else has had this problem (seal seemingly to small) or if I should be adding extra sealant?

01-19-2011, 04:53 PM
wouldn't surprise me if the transom assembly wasn't flat in that area, it's not machined, it's as-cast, the seal is following the groove pattern which may not follow the as-cast surface

01-19-2011, 05:13 PM
wouldn't surprise me if the transom assembly wasn't flat in that area, it's not machined, it's as-cast, the seal is following the groove pattern which may not follow the as-cast surface

Very good point. It was an old assembly that I rebuilt.

01-19-2011, 06:25 PM
seal it with 4200 by 3m..it will at least come off if you ever need to remove it..their shouldn't be any gap between the assembly or the boat's transom..Tighten and torque the bottom bolts first,then do the top bolts,then do the middle bolts..leave it sit over night and follow the torque sequence again...i also seal the around the stud and before i install the inner ring i seal around the studs going through the transom..

start off torquing the bolts @ 20 ft lbs then 5 lb increments to max 35 ft lbs..its also good to use new nuts..

01-19-2011, 06:37 PM
Also, you can lay in a thin bead of 4200 or Life Seal in the groove formed by the transom and the housing. This will help and helps to make up for the irregularities of the housing casting.

Morgan's Cloud
01-19-2011, 08:02 PM
I've never trusted or relied on those O ring transom seals.
Merc or Volvo .. Always goop up prior to assembly/installation with something like Lifecaulk ..3M used to make something good for the job too ..I'm thinking it was '1000' ... not posotive.(the cartridge was white with purple/pinkish lettering.)
The excess trims of like a dream when it's cured and you're not going to need a truck with a tow eye to remove the transom plate later and tear the transom to shreds like if you used 5200.

01-19-2011, 09:41 PM
true that,,, 5200 is almost permanent,, however that transom housing needs to be almost a permanent fixture,,, i worked at a cruisers dealership and we did use 5200 on that piece,,, i thought u were talking about the gimble o-ring

01-20-2011, 11:45 AM
Great responses, all -- thanks. I will use some kind of sealant and then let you know the outcome. I should have trusted my gut when I installed this to begin with...and used sealant against the transom. Lesson learned, thanks again.

01-20-2011, 03:09 PM
If you use a silicone product it must be the aluminum friendly type, regular silicone corrodes aluminum!