Another Leaking Transom Issue

[ScottieScott]

Hi all,

I have a 1986 Mercruiser 170 with an Alpha One Gen 1 outdrive. The last time we had it on the water was a couple of years ago, and we were getting water in the bilge, just sitting in the water, as well as when running.

Fast forward to this season.....I have changed the U-joint bellows, replaced the shift cable and bellows, and put on an exhaust tube. When I checked the old bellows that I removed, they were fine.

This season, I don't get any water in the bilge while running on a hose in the driveway. We took it out this weekend, and we get water again, either sitting, or driving. I am rather certain that the exhaust elbow is still in good shape as I don't see, feel, or hear any water coming into the bilge from there.

The amount of water seems to be a bit more while sitting, but it is a significant amount. I am going to guess that in the 2 hours we were out, we pumped several gallons, and when we pulled the plug when taking out, a couple more gallons came out.

I have checked and rechecked the bellows, the transom is solid, there are no cracks or compromises in the hull.

What other points do I need to check?

I have read where the trim hose manifold gasket might be an issue, and it seems to be filling from the bottom, if that makes sense. Is there anywhere else to check?

The steering cable exit is pretty high isn't it? I would think that this would be out of the water almost completely when running.....and we still get quite a bit of water when running.

Thanks in advance.
Scott

 

[thumpar]

You can rule out exhaust bellows completely. They normally have water in them unless the exhaust pressure blows it out. It could be the manifold for the trim hoses. Did you make sure to use bellows adhesive? You can try to put the nose of the boat up high on the trailer and put water in the bilge to see where it comes out. Just make sure not to get the starter wet.

 

[tinkerguy70]

I had a similar issue with our '84 3.0 A1.
I went through all the motions, as you have, only to find that tightening the transom plate bolts a little bit cured the problem. You might take a look. It certainly won't cost anything to try it.

Well, as long as you don't get crazy with the torque anyway.

 

[ScottieScott]

I left the boat at the lake in storage, and will be back next weekend or two. I will certainly try these two things.

Tinkerguy70. It is possible that your solution might work.....I noticed that there is what I would call an excessive amount of silicone sealer around the bell assembly outside the transom. I wonder if the previous owner had taken that off for some reason and just didn't get it tight enough.

I used bellows adhesive, probably way too much actually.

If it is the trim hose manifold, can I just make a new gasket out of a sheet I had bought from the auto parts store for a different project?

 

[Howard Sterndrive]

I noticed that there is what I would call an excessive amount of silicone sealer around the bell assembly outside the transom. I wonder if the previous owner had taken that off for some reason and just didn't get it tight enough.

I don't think there should be silicone there at all. Could be a rotten transom. Could also be the seal on the exhaust downpipe. On my Gen II, water will leak up the shift linkage and in if the square seal on the nose of the drive isn't on right.

Unfortunately on my boat I had to pull the engine, reinstall the drive and relaunch to find the problem, which was the exhaust Y pipe.. Hope you don't have to go that far.

 

[ScottieScott]

Howard,

I will definitely poke around on the transom, but honestly, it feels really solid, I haven't checked behind the bell housing though.

 

[thumpar]

With the silicone on there is sounds like someone put a bandaid on it. There should only be a seal between the gimbal housing and transom.

 

[tank1949]

I hate to bring bad tiddings, but rot is rot. Salt water will not rot wood but fresh will. If you can, get a strong flash lite and with a buddy and being careful, shine lite under motor as buddy brings boat up to plane and then LOOK carefully. If you can, you may also be able to use a large mirror. You might be lucky and only have a thru-hull fitting that leaks. You might also have a stress crack allowing water to come in under pressure. God help you if transome is rotten. That means pulling motor. DONE that! Nonetheless, you should be able to see water dripping from somewhere!

 

[ScottieScott]

With the silicone on there is sounds like someone put a bandaid on it. There should only be a seal between the gimbal housing and transom.

Interesting.....I was hoping to not have to remove the entire gimbal housing, but it seems that it will probably be inevitable. I would rather do it right though and avoid shortcuts.

 

[ScottieScott]

I hate to bring bad tiddings, but rot is rot. Salt water will not rot wood but fresh will. If you can, get a strong flash lite and with a buddy and being careful, shine lite under motor as buddy brings boat up to plane and then LOOK carefully. If you can, you may also be able to use a large mirror. You might be lucky and only have a thru-hull fitting that leaks. You might also have a stress crack allowing water to come in under pressure. God help you if transome is rotten. That means pulling motor. DONE that! Nonetheless, you should be able to see water dripping from somewhere!

Water leaks in whether or not the boat is running or just anchored. I don't think that being on plane would matter. As for the transom being rotted out.....like I mentioned, feels very solid, and is fiberglass inside and out. There could be a stress crack, but I am leaning toward a bad seal between the transom and gimbal housing. I will nevertheless check it all once I get it all apart.

Thanks all for the quick responses.

 

[500dollar744ti]

A rotten transom will still "feel" solid, you have to know what you're looking for to spot it. One of the tell tale signs of a rotten transom is that someone will put a copious amount of silicon around the drive in an effort to band-aid the leak.

Another way to check for a bad transom is to tie the bow to a dock and reverse a little bit and see if the flow of water increases into the bilge. Reversing will cause the transom to flex in such a way that if it's rotted, more water will pour in.

 

[ScottieScott]

A rotten transom will still "feel" solid, you have to know what you're looking for to spot it. One of the tell tale signs of a rotten transom is that someone will put a copious amount of silicon around the drive in an effort to band-aid the leak.

Another way to check for a bad transom is to tie the bow to a dock and reverse a little bit and see if the flow of water increases into the bilge. Reversing will cause the transom to flex in such a way that if it's rotted, more water will pour in.

I will give this a try. Thanks.

 

[ScottieScott]

Ok, now I am getting a bit concerned about the transom.

A couple more questions:

I can't seem to find any schematics or steps to remove the transom assembly....what should I watch out for? Any instructions out there?

Once I have it removed, what tests can I do to check for the transom rot? I see gel-coat fiberglass on the outside, and fiberglass on the inside.

Any other info or tips would help.

Thanks

 

[JASinIL2006]

From the inside, your best bet is to drill some small holes (maybe a 3/16" bit), about 7/8" deep, into several places of the transom core. (Obvious spots are around/below the outdrive keyhole, below any through-hull fittings (e.g., swim ladder bolts, transducer cable fittings, trim tab lines) particularly those below the water line, and along the lower edge of the transom core. Don't drill all the way thru the hull! You just want to get past the interior fiberglass into the wood. Dry, light (sometimes powdery) shavings are good. Dark or wet shavings are not so good.

If the shavings all look good -- and I hope they do -- you can fill the holes with a marine epoxy (MarineTex or PC-11) or 3M 5200.

 

[Fishermark]

^^^^ The chances are 99% (if not higher) that you have a rotten transom. The smear of silicone is a dead give away.

Like suggested above, go ahead and drill a few holes from the inside. I would be amazed if they come out dry.

To remove the transom assembly, you first pull the outdrive, then the engine, then the exhaust pipe, then the assembly.

 

[ScottieScott]

From the inside, your best bet is to drill some small holes (maybe a 3/16" bit), about 7/8" deep, into several places of the transom core. (Obvious spots are around/below the outdrive keyhole, below any through-hull fittings (e.g., swim ladder bolts, transducer cable fittings, trim tab lines) particularly those below the water line, and along the lower edge of the transom core. Don't drill all the way thru the hull! You just want to get past the interior fiberglass into the wood. Dry, light (sometimes powdery) shavings are good. Dark or wet shavings are not so good.

If the shavings all look good -- and I hope they do -- you can fill the holes with a marine epoxy (MarineTex or PC-11) or 3M 5200.

Thanks for the quick response. I too hope that I am going to see the dry shavings. The boat is almost 30 years old, and this year is the 5th season I have owned it. The 'band-aid' seemed to work for the first two seasons, but noticed a small amount of water coming in late in that second season. We haven't had it in the water last year or the year before so maybe that silicone deteriorated enough the past two years to be a real problem. I guess I had the seller pull a fast one on me. I am not sure at this point I have the patience to remove the entire transom assembly and rebuild the transom, so I am hoping for the best.

 

[Fishermark]

The bottom two bolts are thru bolts made of aluminum - or a similar alloy. You only other hope would be for them to simply be corroded and loose. But again - they corrode and get loose generally only because the transom has gotten wet and rotten. Either way - the only way to remove and replace those bolts is to remove the outdrive and engine.

 

[ScottieScott]

The bottom two bolts are thru bolts made of aluminum - or a similar alloy. You only other hope would be for them to simply be corroded and loose. But again - they corrode and get loose generally only because the transom has gotten wet and rotten. Either way - the only way to remove and replace those bolts is to remove the outdrive and engine.

Well, I an feel another Band-Aid coming on - lol. Only this time with better sealant. We have been looking to trade this one in on a bigger/newer boat. We may be doing that sooner than we planned.

Was considering an alternator conversion kit as well as the battery isn't charging and we had to get a jumpstart. Once with a 3 year old battery, then the next day with a 3 hour old battery. The alternator may be worth it if I can seal the leak for a couple more seasons.

 

[yacaptain]

Check the zinc on the bottom of the trim hose block as mine had corroded and was gone. This let water through the middle of the trim block hole into the boat. The new zinc came with a rubber plug and gasket to cover the hole. Also check to see the trim hose block is tight. I ended up tilting the boat up and putting water inside up to the exhaust outlet and found the water running out of the trim block. Wish I did that before I pulled the engine and replaced the Y pipe o-ring gasket.
Just something else to check.
Good luck.

 

[ScottieScott]

Check the zinc on the bottom of the trim hose block as mine had corroded and was gone. This let water through the middle of the trim block hole into the boat. The new zinc came with a rubber plug and gasket to cover the hole. Also check to see the trim hose block is tight. I ended up tilting the boat up and putting water inside up to the exhaust outlet and found the water running out of the trim block. Wish I did that before I pulled the engine and replaced the Y pipe o-ring gasket.
Just something else to check.
Good luck.

Thanks so much. I have gotten some great ideas from all of you in my efforts to plug this leak as well as other issues I have had. I will definitely check the trim hose manifold - the gasket as well as for the zinc.....