Tucked underneath your engine(s), the lowly engine mounts are out of sight and, mostly, out of mind. But, these four steel and rubber bits of hardware are crucial to the well-being and smooth-running of the whole drive train –engine, transmission, shaft, shaft seal, cutlass bearing and prop.
So, a little care is due. As part of routine maintenance such as changing the engine’s oil, filters and zincs, it is important to shine a light on the engine mounts to see how well they are aging. Aging is the key word because engine mounts deteriorate over time and hours of use. As Indian Jones likes to say about the wear and tear on his body, “It’s not just the years, it’s the mileage.”
The thing about engine mounts is that they do three important jobs. They hold the engine in place even as the boat is bouncing through waves, they reduce vibration and thus the wear on the drive train, and they keep the engine, transmission and shaft aligned.
The two things you need to check are the rubber insulation pads in each mount and the engine’s alignment. The first will deteriorate over time and with exposure to diesel oil. Rubber absorbs oil and expands, which will change the pad’s shape and, oddly, will accelerate decomposition.
Poke the pads with a knife to see if the rubber is perishing. If bits come off easily, they are toast and need to be replaced.
Next check the engine’s alignment, particularly if you have shaft vibration. This won’t be a problem if your drive train has a soft shaft mount on the transmission that ameliorates misalignment. But on a hard links, you need to check for any gaps between the plates where the transmission meets the shaft. This is done with a feeler gauge. Check your engine’s manual for acceptable gaps.
If you need to adjust the alignment, you do so by torquing the engine mounts until the link plates meet without gaps on one side or the other. This is a trial and error process.
Replacing engine mounts or the rubber insulation pads is no small DYI operation. If you are a mechanic, fine. If not, it’s time to call the pros.
Here’s a good summary of all things to do with your engine mounts on BoatUS’s website.
