Sterndrives, also called inboard/outboards or outdrives, have been around for some 60 years and have attained a high degree of engineering refinement. Part of their attraction is their inexpensive power sources, namely four-stroke automotive engine blocks. They can provide outstanding performance and service life in fresh or salt water—if they are properly maintained. Critical maintenance areas are the bellows and gimbal bearing systems. Neglecting maintenance of these systems not only causes damage, but it also places your vessel at risk of water intrusion resulting in swamping or sinking.
Keeping Water From Entering The Hull
When you start and engage the driveline of a sterndrive, a lot goes on through the transom of your boat. Engine power reaches the sterndrive through the drive shaft. Engine exhaust flows through the transom through the drive and exits beneath the waterline at the prop.
Multiple functions begin inside the boat and end at the sterndrive. There are three necessary penetrations through your transom at or below the waterline: the shift cable, the drive shaft and the exhaust. The only part that keeps the water outside the hull is the sterndrive’s bellows system. These are flexible, ribbed black rubber moldings that are clamped to the boat’s transom and the sterndrive. According to BoatUS, failure of the bellows is the second most common cause of boat sinkings at the dock.
Bellows must be flexible to allow steering and tilting and maintain that flexibility without fracturing under seasonal temperature swings, moisture and dryness, UV ray absorption, vibration and mechanical abrasion. If the bellows fail, they can let enough water into the boat to sink it. Sterndrive bellows require inspection and maintenance on a regular basis.
Thorough bellows inspection is only possible when the boat is out of the water — on a lift, a work stand at the marina, or while secured on its trailer. You will have to be sure there are no obstructions preventing steering or tilting through the drive’s entire range in order to access all of the bellows. 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. However, if one bellows is bad, you should change all three.
Our Club commander, Pete Stevenson, is a professional marine surveyor who has experience evaluating thousands of sterndrives over his career. Pete has a good advice about sterndrive bellows maintenance that all owners should heed.
- “I have seen several instances of bellows failure with sinking or damage as a result.
- “I recommend checking the bellows at every haul out. The process is easy. Raise the drive to trailer height, get up close and personal and put your fingers on the bellows. If they are soft and pliable to the touch and no cracks or cuts are visible, you are pretty good to go. If they are hard and stiff you are on borrowed time. The bellows must be soft and pliable so they can articulate with the drive. Hard and stiff equals stress resulting in cracks.
- “Leaving the boat in the water or on the hard with the drive up invites problems. Critters like muskrats and their cousins are attracted to salt in the rubber. The raised drive gives them access. In addition, leaving the drive up on the hard invites rain water to pool in the lower unit. This can have unpleasant consequences if there is a hard freeze.
- “I think a planned change out of bellows and gimbal bearing every five years is a good idea.”
Bearing Inspection And Maintenance
Beneath the drive shaft/u-joint bellows, you will see the gimbal housing assembly, which should be checked and serviced every season. The gimbal bearing in the housing supports the driveshaft from the drive as it passes through the gimbal housing assembly to the drive coupler. Water, lack of grease and wear can cause the bearing to fail.
With the drive removed:
- Check for water in the u-joint bellows.
- Grease the u-joints if zerk fittings are provided.
- Check the gimbal bearing.
- Check the shift cable pocket area and lever.
- Check all the rubber components.
- Check for play or looseness in the steering.
- Check for play or looseness at the side hinge pins.
- Check your engine alignment.
Learning The Hard Way
Do you have any experience with bellows or general sterndrive maintenance to share with Club members? Consider writing them up as a comment to this post.
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