Drive bellows: when they need replacing and what the job involves

When should the bellows be replaced?

Replace it when the maintenance schedule in your drive's owner's manual says so, and right away if you find a crack or a hole. Intervals differ between drive models, so look up your specific drive. Volvo Penta SX and MerCruiser Alpha One each have their own schedule. A damaged U-joint bellows lets water into joints and bearings that should stay dry.

Replace the bellows with the boat securely blocked up on land, following the service manual for the drive. Look up your drive in the drive catalogue before you buy parts. The engine's horsepower and the boat's model year won't help here.

The U-joint bellows and the exhaust bellows do different jobs

The U-joint bellows seals around the drive shaft joints. The exhaust bellows carries the exhaust on drives that have one. A drive can also have other bellows and seals, for example for the shift cable. Find out which part has split before you order.

If you have a sailboat with a saildrive, a diaphragm seals against the hull. That is a different design with its own maintenance instructions. Look up the right exploded view and part name before you order a bellows kit.

How to find the right parts

• Write down the make, full drive designation and serial number.
• Find out whether the drive or parts of it have been replaced before.
• Match bellows, clamps, seals and single-use parts against the manufacturer's parts catalogue.
• Check which adhesives, sealants and special tools the instructions call for.

Example: Volvo Penta SX, 280 and MerCruiser Alpha One Gen II are different designs, each with its own instructions. Then look up the parts for your model in the parts catalogue.

What a proper replacement involves

First the boat is secured and the drive supported so its weight doesn't hang on the mounting. Then it's taken apart as the manual describes. Once the old bellows is off, the sealing surfaces, joints and bearings are checked for water, corrosion and wear. If water has already got in, a new bellows alone won't fix it.

The new bellows is fitted the right way round, with the clamps in the right place and using the products the manual specifies. Torques and fitting positions vary between models and are given in the manual. A badly fitted bellows can leak even when it's new.

DIY or hire a yard?

Let a workshop do the job if you lack lifting gear, special tools or experience taking a drive apart. Ask for a quote that lists the bellows replacement separately from bearings, joints and other parts. State that any extra work must be approved by you first.

Afterwards the drive should move, seal and work as the manufacturer specifies. Note the date, drive number and which parts were fitted. Check for leaks at launch and after the first trip. A bellows replacement goes well with a gear oil change, but a regular oil change does not include the bellows.

Frequently asked questions