The Care And Feeding Of Sterndrives

Here's an article by Doug Alling on caring for your sterndrive. Good Reading!!

Keeping your sterndrive in tip-top shape will add years to its life — and help to keep your boat afloat.

Giving your sterndrive some attention now can prevent major problems later. (Photo: Volvo Penta)

Sterndrives were first commercially introduced in the early 1960s, and came to dominate the boat propulsion market in short order. The biggest names in the sterndrive game today are Mercury and Volvo with thousands of older Outboard Marine Corporation (OMC) drives still in use but no longer being produced.

When you power up your engine and pull away from the dock, you set in motion a lot of activity at the stern of your boat. You push the throttle, engaging the prop. Power from your engine is transferred to the sterndrive via the drive shaft. Exhaust is pushed from the engine and exits at your prop. All of these functions start inside your boat and end at the sterndrive and require holes through the transom of your boat, at or below the waterline. Three to be exact: One for the throttle cable, one for the drive shaft, and one for the exhaust. And there's only one thing that keeps the water outside the boat from entering those openings — the sterndrive's bellows, those black corrugated rubber things that are clamped to the boat's transom and sterndrive in a place that makes them really hard to see. Perhaps the old saying, "out of sight, out of mind," is why bellows become such a big issue when it comes to sinkings. Take away the biggest and most obvious cause of boat sinkings at the dock — hurricanes — what do you think comes in second place? If you guessed sterndrive bellows failures, take a bow.

Ignoring your sterndrive now can cost you money and down time next season.

Take a moment to think about the environment that bellows operate in and the work they are tasked to do. They are exposed to hot and cold, wet and dry, vibration, UV, and marine life (sharp barnacles), and through all that they are expected to stretch, expand, and contract as you tilt and steer your sterndrive. Bellows will wear out — and when they do, they can easily let enough water into the boat to sink it. To keep your sterndrive-powered boat afloat, bellows require inspection and maintenance on a regular basis.

Bellows Inspection And Maintenance

Inspection of the bellows can be accomplished while the boat is out of the water — on a lift, a work stand at the marina, or on its trailer. Keep safety in mind while doing this! Make sure the boat is properly supported and if on the trailer, chock the trailer tires. It is good practice to make sure that there's no way the engine can be started while you are performing your inspection by disconnecting the batteries. The inspection area is tight and will require moving the sterndrive from one position to another — port and starboard, up and down — to access as much of the bellows as possible. The inspection is as simple as taking a close look (a flashlight is required) at the condition of the rubber bellows and their clamps. Are there any obvious signs of cracking? Is the rubber becoming brittle? Is there any rust showing on the bellows? Do the stainless steel clamps show any signs of corrosion? If you spot any marine growth (barnacles, mussels, or the like), they have got to go. Barnacles and broken shells can be razor sharp and your rubber bellows won't stand a chance against them.

Marine growth can be razor sharp and slice open bellows, allowing water into
the boat. Inspect bellows frequently throughout the season. (Photo: Doug Alling)

That's what to look for outside of the boat. Inside the boat, look for any water tracks at the transom pass-throughs and standing water in the bilge. If your bilge pump has been cycling on and off, it's time to inspect the bellows. OK, we've done our inspection and things look good, but keep in mind that all manufacturers have a recommended replacement schedule for your sterndrive bellows. You will most likely find it in your owner's manual and you should adhere to it. If you are unsure or can't find the information, a call to the manufacturer's customer service center is in order. I have dealt with both Mercury and Volvo in this regard and both manufacturers have been very responsive. Even if your bellows inspection shows good results, the manufacturer knows best when it comes to keeping them in tip-top shape and how often they should be changed. Most manufacturers agree that a 5-year-old bellows is living on borrowed time. Not replacing it is inviting water into your boat.

If you poke around the Web, you'll undoubtedly find videos posted on how to change out your exhaust bellows while the sterndrive is still attached to the boat. It can be done — with really small hands and the right tools. But the exhaust bellows is the only one that can be changed while the sterndrive is attached. The other two bellows contain the drive shaft and shift cable, and they can only be changed by removing the sterndrive from the boat and disconnecting those systems. Changing out the exhaust bellows alone goes against one of the first rules that a marine surveyor learns: If something breaks or wears out underwater (a bad cutless bearing, a bent rudder) and there are two or more of them, you must always check them ALL. If you are going to the trouble of changing the exhaust bellows, replace the other two, period.