Yamaha Hydradrive loose steering
Our boat with twin Yamaha diesel sterndrives was behaving erratically when accelerating or decelerating. On close inspection we found the steering connections between the drives had over a foot in free play. That is, when we grabbed both drives and pushed them together by hand and then apart, there was over 30 cm of free play.
On closer inspection we found that the steering arm that comes out of the gimbal housing has a bolt that clamps it tight onto the steering shaft. The problem is the seal of the steering shaft eventually leaks and corrosion and wear make the steering arm loose in the shaft. You cannot tighten the bolt any further as it has a ridge on it where the thread ends that prevents it getting any tighter. As a matter of fact even loosening it was extremely difficult as it was rusted in and access is tight from inside the engine bay through the transom. A 6 point 19mm socket, a short extension, a very long bar and lots of patience was required.
Alex's solution to tighten up the steering was to machine off the ridge using a lathe. Of course Alex has a lathe at home and perhaps not everyone has, so I guess the option is to get someone else to do it or get a bolt without a ridge. We thought it best to use the lathe and only take a few millimetres off as we didn't want to over stress the steering arm clamp and risk a fracture by over tightening.
The photo shows the difference between the standard bolt and the machined bolt. Machined version on right and below.
The steering is now much better.