Sterndrive bellows are rubber “boots” that seal out water around the exhaust, U-joints and shift cable, while allowing the drive to pivot and tilt. These can wear out and require regular replacement (see owner’s manual for service intervals).
Before anything, take off the drive (check out boatingmag.com/stern-drive-bellows), and once you do, replace all bellows at once. For now, let’s focus on the exhaust bellows, using the MerCruiser Alpha One as an example (counterclockwise from top).
Skill Level: 3/5
Time to Complete: 4 hours
Tools and Supplies
*Transom service kit with exhaust bellows for MerCruiser Alpha One (from $62.95, amazon.com)
*Bellows expander tool, Quicksilver part No. 91-45497A1 ($57.95, michiganmotorz.com)
*Bellows adhesive, Quicksilver part No. 92-86166-Q1 ($10.86, go2marine.com)
*Socket wrench set (½-inch drive)
*Socket wrench set with an extension (¼-inch drive)
*Knife (to slit old bellows)
*Flat-head screwdriver set
*Open-end/box wrench set
1. Remove the Exhaust Bellows
With drive unit removed from the bell housing, block the bell housing in the full up position and loosen the screws for the two clamps at either end of the exhaust bellows. Access the aft clamp from underneath. To loosen the clamp at the transom housing, insert a quarter-inch extension with a socket wrench through the access hole on the port side of the transom housing. With clamps removed, slit each end of the bellows with a sharp knife (while being careful to avoid damaging other parts) to allow for easy removal.
2. Install the Bellows on the Forward Mount
Use solvent to clean the mounting bosses, and then apply bellows adhesive (Quicksilver part No. 92-86166-Q1) to the transom-housing mounting boss. Put a hose clamp over one end of the bellows so that the clamp screw is on top of the bellows (indicated by the split line on the bellows) and facing the access hole on the transom housing. Slide the ground clip to the lower edge of the bellows, push the bellows fully on the transom-housing mounting boss, and tighten it to the manufacturer’s specs.
3. Position the Bellows on the Aft Mount
Remove the upper shift shaft, shift crank and Teflon washer. Apply bellows adhesive on the bell-housing mount and install the clamp on the aft end of the bellows, fitting the ground clip under the bellows. Slide the bellows expander tool (Quicksilver part No. 91-45497A1) through the bell-housing mount and into the bellows, and align the U-shaped plates with the third fold of the bellows. Squeeze the scissorlike handle of the tool to expand the bellows and then pull the handle to slide the bellows onto the bell-housing mount. Stop pulling when the retaining pin holes align with the aft bell-housing surface; then slide the retaining pin through both holes and insert the retaining clip through the small holes at the end of the handle, and release the handle.
4. Tighten the Aft Clamp
Position the clamp screw at the bottom of the bellows so that it faces down on the opposite side from the water hose. Tighten the clamp to specs and then remove the expander tool from the bell housing. Reinstall the upper shift shaft, shift crank and Teflon washer. Allow the bellows adhesive to dry for at least an hour. Reinstall the drive unit once all bellows have been replaced.
Quick Tip: Use a socket wrench or nut driver to tighten hose clamps. Screwdrivers work but can damage bellows if they slip off.