Water in bellows - but dry bilge - how?

[ChiefScientist]

I have owned this 2008 280da with a single 496B3 since new. It has stayed in the water year round the last three years - except for service. It's now berths in a covered slip.

Two weeks ago, I could hear the typical louder noise of a failing gimble bearing and the occasional mild knock of a failing u-joint. I'm familiar with these sounds from my runabout with an alpha one. I had a mechanic listen to them boat in the water because I wasn't sure - and the indicator of bellows trouble (water in the bilge) was absent. After we listened a while and tested the drive in reverse, turned to port, starboard, etc., we decided there was a problem despite the dry bilge. So, I had the boat pulled. Sure enough, there was water in the bellows. The u-joint was badly rusted. The gimble is equally bad.

Given the extent of the rust, I would expect a serious leak. I would expect the leak would be easy to find. I would expect water to be in the bilge.

Now the mystery. The bilge on the boat is always bone dry. The only water that has ever been in the bilge is the minor amount of water when I would use the single point drain system. Suck it out with a shop vac and the bilge is back to bone dry.

Where did the water go that obviously caused the damage?

More importantly, how can one guard against extensive hard parts damage when there is a leak but the bilge stays dry?

We thought about a transient leak like a bad bellows sealing job, or maybe a pinhole. But the mechanic could not find a pin hole in the bellows. In fact, there is no damage at all after 300 plus hours on the outdrive. Not even a prop ding.

What are your thoughts? Thank you!

 

[Henry Boyd]

The gimbal bearing can act as a dam and small amounts of liquid will stay on the drive side of the bearing. I had this happen with a bad top seal on the drive that dumped grease into the cavity and drained the fill bottle several times before it leaked into the bilg.

Maybe no pinholes in the bellows, but what about the possibility of the seal between the bellows and drive weeping? One hundred percent in water could cause moisture to pass into the bellows cavity via osmosis through the bellows material. The bellows by the way if original are overdue for replacement.

Yes, corrosion can damage the gimbal bearing and drive u-joints, but corrosion on those points does not necessarily mean it was the cause of failure. Poor lubrication, a plugged zerk fitting, and/or sloppy maintenance can do in the gimbal bearing from lack of lubrication. Starting the engine with the drive in the up position can cause excessive u-joint wear, as will moving the boat with the drive trimmed up into the trailer range.

Fix the bearings and do a bellows job.

Henry


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[ChiefScientist]

Henry - thank you for your always great answers. You nailed the next steps obviously. I might add its the last two years the boat is slipped all year except for maintenance.

The bellows was visually inspected in June when the boat was bottom painted and a bow thruster installed. At some point I will post the general satisfaction bow thruster experience in the 280 forum. We all agreed, the upper bellows looked fine and no need to replace in as much as you can see. The consensus was go until the next year.

The damage to the joint and gimble in this case is rust although I agree the others are possible.

On my SeaCore, there is no need to pull the drive to grease the u-joints. Thus - no need to annually pull the drive. And now, the gimble bearing that is replacing this rusted one is a "no grease" system. They pull the Zerk and put in a plug! Yeah!! This is an upgrade IMHO with one less leak source. I'm am also assuming they will put in the new style exhaust bellows that is only connected when the drive is down. Pulling the drive now is only necessary now to do a bellows job.

What concerns me is there is NO WAY to check for water in the bellows. And water in the bellows can happen anytime due to damage, capillary action between the drive and bellows, etc. I supposed, during the winter, when the exposed part of drive may be far colder than the water, you will build condensation from the warmer engine compartment! And you could have an immediate leak due to a production issue or a bad bellows job. The hard parts are really expensive and an inspection method or warning system is really needed. I'm not sure this is a tenable situation.

I really believe stern drive manufactures should have developed a monitoring system by now.

 

[ChiefScientist]

When I started looking around, it appears Volvo in its OceanX series drives has a "water in bellows" sensor. Hmmmmm.

 

[Henry Boyd]

I wasn't sure when the zerk was discontinued. I got the same upgrade when we replaced the transom assembly last spring. Time will tell if it's a plus.

I also should have mentioned that bellows tend to get porous as they age. It wouldn't take a lot of water to degrade the bearings. Also the BIII drive gets pretty hot, so small amounts of water trapped between the drive and the gimbal bearing would probably evaporate and either vent into the er, or condense on the bearing and drive shaft. Makes me wonder how effective a water sensor would be except for a complete failure.

Henry


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