I have a squeaky noise in the drive shaft that changes with the engine's rpms. Any ideas on what it is and how to fix it?
Mark Matthews responds:
The noise you are referring to is likely caused by a worn cutlass bearing. The cutlass bearing consists of a metal or fiberglass pipe with a ribbed rubber insert in which the shaft rides. The idea is that water is allowed to circulate up the grooves to lubricate the bearing, and that bearing supports the shaft as it exits the boat.
If the engine has been properly aligned, the cutlass bearing should last for years. If the engine has been misaligned, then the cutlass bearing will wear out much faster, causing some peculiar noises in the process.
Anytime a new sound comes from this critical part of the boat, it's a good idea to have a look at it, whether that means getting a diver, or going over the side yourself, to see if there's anything fouled in the prop. It's also worth noting the type of water. In silty water cutlass bearings wear out faster because foreign material often circulates inside the bearing. In any event, now is the time to ask yourself when was the last time the bearing was changed?
Some cutlass bearings inhabit struts, while others are incased in housings. There is no other way to repair a cutlass bearing other than to remove it and to put in a new one. The next time the boat is out of the water for maintenance, grab the prop and shake the shaft. Minimal play is OK, anything more than that and the bearing likely needs to be replaced.
To do that, the prop will need to come off, the rudder may have to be dropped, the coupling will need to come apart, and the shaft will have to be removed. Some cutlass bearings are held in by small setscrews, usually covered by several layers of bottom paint. Most, however, are friction fits and can be tapped out using a dowel.
If you have more questions, I'd refer you to either Don Casey's This Old Boat or Nigel Calder's classic Boatowners Mechanical and Electrical Manual. Best of luck to you in resolving your noise problems.