Engine mounts sit between the engine's feet and the bearers it's bolted to. Each is a block of rubber bonded to steel, with a threaded stud that sets the engine's height. They hold the engine in line with the shaft and keep its vibration out of the hull.
The rubber wears out quietly: it hardens, cracks, swells with oil or tears from its metal. Once a mount fails, the engine moves, and the shaft and cutless bearing take the strain.
What a surveyor checks
Practical Sailor's Marc Robic starts with two questions: is there rubber dust round the mounts, and is there abnormal vibration. Look for cracked rubber, rubber parting from its metal, oil soaking and collapse. Power & Motoryacht's quick test: if the engine bracket sits all the way down on the stud, the rubber has collapsed. On the sea trial, watch the engine go into gear: a corner that lifts in reverse has a failed mount.
In the report
"Engine mounts, aft port mount rubber separated from its base plate, engine lifts visibly at that corner when shifted into reverse. Replace all four mounts and realign the shaft." See failed engine mounts.