You decided your engine mounts need to be replaced. While waiting for your engine mounts to arrive, start by inspecting your engine.
Water, oil, and coolant leaks must be repaired now. As you read in Your Boats Motor Mounts what to Consider and Inspect these things will deteriorate the elastomer of the new engine mounts. Make sure you also inspect the exhaust mixer elbow carefully; it might be leaking. Fix it now. It will take longer than you think for this repair.
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Clean what you can of the engine mount beds now to help with your next task. Now using a felt tip marker, place a mark on the engine bed and on the engine mounting arm so you can duplicate the measurements you are now going to be taking. Measure the heights of each mount above the engine bed. Make a sketch of the engine and write the dimensions down on the sketch. A digital caliper is a must for this job. Repeat the measurements several times to be certain of your readings. These measurements will help in aligning the engine on the new mounts.
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Take time to squirt a rust-breaking solvent onto the bolts holding the engine mounts to the engine bed, and to the nuts above and below the stud that fastens the mount to the engine. Getting all these fasteners free is important.
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With a felt tip marker, make a mark on the two halves of the shaft coupling before removing the coupling bolts. Using a flat-blade screwdriver, separate the coupling halves an inch or so to allow the engine to move free of the shaft. Soak the bolts in some rust remover if needed. Do not try to raise the engine without first disconnecting the shaft coupling.
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Replacing our Engine Mounts and Alignment
The next step is to raise the engine off the mounts by using the adjusting nuts on each mount. Remove all four of the top nuts holding the engine down to the mounts. You will also want some wooden blocks to place under the engine when raising it. Now start adjusting the bottom nut on the mounts raising the engine. Be careful and think your way through each step. Replace one mount at a time, as you do not want the engine to fall.
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Before removing each mount, note the position of the enlarged mounting hole or slot on one end of the old mount. Install the new mount the same way.
Clean the engine bed of rust and debris before installing the new mount. Install all the bed bolts in each mount, but do not tighten them all the way yet, as you will need to move the mounts to align the engine.
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After all, four new mounts are installed, and the engine lowered onto them, let the engine sit for a day or so to settle. The elastomer will compress a little. If you try to align the engine right away after replacing the mounts, the engine will drop some on the new mounts and your fresh alignment job will turn out to have been for nothing.
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Now using your digital calipers, restore the engine to the original height per your drawing. Carefully clean both faces of the shaft coupling as any grit or corrosion will prevent an accurate alignment. Reconnect the halves of the shaft coupling. Remember to observe the marks you added to return the coupling halves to their original orientation. Install only one coupling bolt and nut loosely — just barely finger-tight. Using a feeler gauge, align the engine horizontally and then vertically. A rule of thumb is to get the alignment to less than one thousandth of an inch, per inch of coupling diameter. Or, to within 0.004 thousandths of an inch for a four-inch diameter coupling.
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Repeat the vertical and horizontal alignments of the engine a few times, as each adjustment will change the other. Take your time and get the engine aligned as close to perfection as possible. There are several good YouTube videos on how to align a shaft or coupling if you have not done this before.
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After making an adjustment, give the engine a few good shakes to make sure it settled to where it should be, before checking the alignment with the feeler gauge. When you are satisfied with the alignment, and using the same bolt holes, you may want to remove one bolt at a time. Add a little bit of epoxy into the wooden bolt holes. Tighten the engine mount bolts as you replace the bolt into the epoxy wetted hole. If one or more of the engine bed bolt holes require re-drilling, a right-angle drill will make quick work of the job.
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Check the alignment once more with the feeler gauge and replace the coupling bolts after cleaning the threads with acetone and applying some Blue Loctite on the threads of each bolt.
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Check all the engine mount bolts for tightness before starting the engine.
Run the engine in gear, over a wide range of RPM's, in both forward and reverse Listening to your boat and Feeling your boat for any vibration. Shut the engine down and re-check all bolts and nuts for tightness.
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