Maintenance with Marc: Your engine mounts – do they need replacing? Part 1
Sept 22, 2022
by Marc Robic
Do you have abnormal engine vibration; rubber dust around engine mounts; telltale signs of possible engine mount wear or imminent failure?
check the engine mounts for wear
It is always discomforting when you know, and actually feel, that something is not quite right.
For a little while now, while navigating under power, I felt some “new” vibrations that simply disturbed me. Putting the boat safely on auto pilot, I went down into the cabin, opened up the rear engine cowl and realized it was the propeller shaft that seemed to be the origin of the vibration. Either caused by poor shaft alignment (which I determined was not the case) or something else was causing this issue.
While inspecting the engine mounts, the most likely culprits, I noticed the rear port side engine mount was leaving a lot of rubber dust and residue around itself. With the engine stopped, I was able to move or twist the mount by hand. These are telltale signs of engine mount wear and, in the case of that particular mount, a possible and imminent mount failure – which is the last thing anyone of us would want! Consider other collateral damage that could possibly cause.
telltale signs
With the engine mount so worn, in addition to its proximity to the transmission and prop shaft link, this is what was causing the excess vibration while under load (forward or reverse). Plus, it means the starboard rear mount has been compensating by taking on extra stress, therefore also getting more wear and tear.
As the mounts are original (27 years old), it would make no sense to change just one. Is it more work? Yes of course, but if one is about to fail, the chances are, the others are not far behind. So, using my philosophy that “maintenance costs much less than repairs”, I ordered four new engine mounts. For our boat, the engine is a Perkins M20 diesel, so I ordered these from Part 4 Engines in the UK. I also ordered the matching hardware. If you’re going to change things like engine mounts, you might as well change the nuts and bolts too.
Marc Robic holding a new engine mount
Another thing I consider important when changing engine mounts on a sailboat, is to make sure the mast is up and the rigging tension is properly set, as this will ensure proper prop shaft alignment. I also recommend having the boat in the water and not sitting on a cradle or trailer for the same reason. At least, plan the final engine to prop alignment when she’s in the drink and the rigging is properly tensioned.
In most cases, the tools needed are basic. Proper size wrenches, a ratchet, sockets and extensions and a sparkplug feeler gauge set. I also used the space saver scissor action jack from my car to hold the engine in place as a backup safety while I removed and replaced each mount one at a time.
Marc continues his project Part 2 in the next edition of CYOB
Marc Robic
Marc is a member of the Canadian Power & Sail Squadron. He and his wife sail their Catalina 270, Aquaholic 3, out of the Ile-Perrot Yacht Club in Montreal, where Marc spent 16 years as Harbour Master. They are regular Caribbean bareboat yacht charterers. With over 40-years experience, Marc is also an avid onboard do-it-yourselfer.
