I'll share an experience referencing back to sailingdog's list of things to check in a survey - Motor Mounts.
Prior to purchasing our current boat, we made multiple inspections, a trial sail and SAM survey. As a result, came up with a short list of defects for the previous owner to repair
prior to sale, and I was very confident in what I knew I purchased.
We have a 72hp Mercedes Diesel engine weighing approx. 640 lbs. The boat was originally fitted with an engine drive compressor for refrigeration. We removed the compressor and opted to re-fit for a battery powered unit.
I believe this was a significant change which resulted in the engine moving forward off its mounts by 3 ˝ inches. Unknown to us at the time, we luckily motored home in this condition without known serious damage. In fact after the initial inspection I had to call a dock buddy for a second opinion because I couldn’t believe what I was seeing.
During the repair
we found that 2 of 4 mounts broke long before I bought the boat, realized by traces of rust on the post at the break point. We also believe the old compressor and belt held the engine in place, but by removing it added further pressure on the mounts to the breaking point.
Although this may have been a very difficult defect to find, lessons learned – when buying an older boat, motor mounts would be considered one of the first things to replace, for peace of mind and savings in the long run.
The inspections and surveys paid off – after our first year we had no other problems, the engine purrs, and we are very happy with what we bought.