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Old 05-08-2008, 08:23   #1
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Changing Engine Mounts

Hello, I am new to the forum and have a question on changing the engine mounts on my boat.

I just purchased a 1990 44' Tolly Craft with twin 400 6v53 Detroit diesel motors. The engine mounts are rusted pretty badly on the outboard side of both motors, due to pinhole leaks in the mufflers that sprayed them with a lot of salt water. I plan to change all the mounts while I am at it. I have owned boats for 25 years, but this is the largest and most complex. I have a lot of mechanical experience from growing up on the farm, and building my own race cars from the ground up, plus I have always done all my own boat maintenance, including a complete engine overhaul on my own.

I can see that I remove the bolts between the engine and the shaft and that is where the alignment must be correct when I am done. I have found instructions on aligning it that say for every inch of plate diameter, you have .001" of alignment tolerance plate to plate. I can't find any instructions on runout when the engine is turned over by hand. Is there any allowed and is the information on the plate to plate tolerance correct?

I am determining the best way to lift the motor to change the mounts. Are there any suggestions, like do you do both fronts with one lift, or both sides? Any suggestions on jacking points. I assume that all jacking must be done against the stringers and never the hull. I plan to rent a hydraulic porta-jack to do the lifting and to move things if needed for the alignment.

Any feedback will be appreciated.

Dave
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Old 05-08-2008, 10:12   #2
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Are your engines located under the floor of the main salon, or under the cockpit sole? Can the sole be easily removed to allow full access to the engine below?
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Old 05-08-2008, 11:58   #3
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The engines are under the sole of the salon, and there are 3 large hatches to access the compartment. The outboard sides of both motor are very tight to the fuel tanks, but there is room to work. The bolts on all the mounts can be accessed fairly easily without needing to get down into the narro space. As in all boats, there is not much room.

I was looking at the setup today to see where it could be jacked, and it looks like it would be the easiest to do each side, rather than doing front and rear pairs. It also looks like I could move some wiring cables off of the stringer and get a small pod jack between the stringer and the exhaust manifol to lift the motor.

Dave
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Old 05-08-2008, 14:18   #4
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The standard technique is to use an A-frame support, spanning the engine bay, with its axis mounted directly above the lifting eyes on the engine. If you look, you should see them. You use a standard chain hoist to raise the engines, one at a time, after removing the shaft coupling. Replace all of the mounts, trying to keep the adjustment as close to the original elevations as possible, then lower the mounts to the bed and secure them loosely. Using the chain hoist to assist, and a couple of short two by fours for leverage (and some helpers, if possible), move the engine aft to mate with the shaft coupling. Slowly, adjust each of the mounts so as to bring the coupling flanges into close alignment. Then, place the coupling bolts loosely in the flange of the coupling, with the nuts and washers on the engine side of the engine coupling. Now begins the close work. You need to get the flanges to touch at one edge, and be only out of alignment at the other side by no more than 0.004 of an inch, using a leaf gauge. That means a fair amount of raising and lowering the adjustment nuts on the mounts. There should be two nuts on the lower side, one above. The lowest nut is a lock nut to keep the adjustment from loosening when the engine is vibrating. This is a pretty generalized explanation. Are you comfortable enough with that or do you need more detail?
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Old 05-08-2008, 18:37   #5
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No, I understand the instructions. Now to find an A-frame to lift the motors.

Thanks for the information.

Dave
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Old 05-08-2008, 20:38   #6
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You can build one with lumber, 2 X 6's for legs and doubled 2X6's for the span. The structure looks like a big sawhorse. Or you might be able to rent one from a rental company or engine shop
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