How To Size For The Correct Marine Engine Mount

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In a conventional inboard application, the engine mount is the single connection between the engine’s power and the vessel’s hull, allowing the vessel to move. The engine mount mitigates engine vibration for your comfort and helps reduce equipment fatigue.

As with any marine mounts, correct installation is critical to getting the best performance out of the mounts to reduce vibration and maximize performance.

Before you even start, you’ll need to select the correct mount. This comes down to sizing. Here are 2 important components of proper sizing: knowing the mount configuration, and knowing what needs to be measured.

Mount configuration – Is it a “4” or a “6”?

A marine engine typically has either a 4-mount or 6-mount configuration.

Typical 4 and 6 mount system

Your engine and transmission mounting points are dictated by the engine manufacturer and should be used to determine the appropriate mount core selection for a balanced system.

Your engine mounting points can be:

  • 2 on the engine, 2 on the gearbox
  • 2 on the engine, 2 on the bell housing, and 2 on the gearbox
  • 2 on the engine, 4 on the gearbox

 

What needs to be measured?

You’ll need calipers, a tape measure, pen and paper. If you’re replacing existing mounts, here are the mount dimensions you’ll need to record either in millimeters or inches.

 

Stud diameter
This is the engine bracket hole size.

Stud centers (if it’s a double stud mount)
This is the distance from center to center of the studs in a double stud mount.

Engine mount base bolt centers
This is the distance from center to center of the bolts that hold the mount base down.

Overall length of the mount
This means the length of the mount’s base, as shown.

Free height
This is the height from engine bed or stringer to the underside of the engine bracket.

Free height is very important when measuring your mounts for fit. This space between the engine bed and engine bracket should be as close as possible to the minimum heights of your selected mounts. This will ensure enough range of adjustment to correctly balance and align the engine package.

 

Once you know your current mount configuration, engine details and size requirements, you’ll be ready to proceed to mount selection. The more information you have on-hand, the better.

Refer to the handy Isoflex Engine Mount Sizing Sheet for a convenient guide to help you gather all the necessary details.