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Old 29-11-2019, 21:05   #1
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Custom Jacks for Replacement of Engine Mounts

I own a 1984 Liberty 458 which is powered by a Perkins 4-236. Back in the summer I let a friend use the vessel while I was working away. I came home, all seemed well and I spent the rest of the season sailing and motoring the vessel from Lake Erie up the Detroit and St. Clair Rivers to Lake Huron. In all, I put on around 100hrs including a rough 18hrs motoring in up to 8ft sig waves on Lake Huron. The only thing I thought strange was, motoring from turbid Western Lake Erie into the crystal clear Lake Huron, I could see through the water that there was a rope wrapped around the propeller shaft. I thought this strange and I couldn't recall any incident when it happened but I assumed I must have run over a fish trap or something. The rope didnt appear to be causing any harm, the water was cold and I am soft. With haulout only a week or two away, I opted to leave the rope till I hauled out rather than jump overboard into the cold Lake Huron water to remove the rope.

The engine ran well the whole time with no noticeably excessive vibration.

You can imagine how shocked I was when, during the end of season oil change, I noticed that the two forward engine mounts were cracked and the aft two were severely dislodged. The engine was riding on the engine stringers with nothing but gravity holding it in place. Yipes! How did this happen? When did it happen?

A quick Google later and I learned that wrapping a rope around the prop can cause engine mounts to crack. Huh. You don't say...

Suspiciously, there was on deck a 3/4" dockline with a ragged end. I knew I hadn't had any incident to damage the dockline and so I wondered if perhaps the damage had occurred when my friend was using the boat. I called to ask if he had had any incident.
“Well, there was that one time that the engine stopped”
“Stopped? How did it stop?”
“Well, I was idling along and it stopped”
“Idling? How many revs? 700rpm? 800rpm?”
“Oh, more like about 1700rpm”
“1700rpm is nearly max torque. I think the engine was trying to exit the boat!!”.
“Oh”

…___...

So, I work offshore and, while I was at sea, I had a month to ponder just how I was going to lift the 1400lb Perkins 4-236 the required 6” or so needed in order to remove the old engine mounts and slide in new. I read at lot of creative ideas including using inflated basketballs and fenders to raise the engine. That may well have worked in principle but my engine pan is just made from sheet steel with no support underneath it and though inflated bags might have lifted the engine, there was no support below the bags.
The Liberty is a center cockpit and, in principle, I could have removed the cockpit floor to gain access to the engine bay but there is so much cabnitry, wiring, plumbing etc that would have had to come out it would have been a multi-week project with untold havoc incurred when it came time to re-instate everything.

Instead, I had to come up with some way to support the engine using the available stringers. I devised two screw jacks consisting of a steel U-shaped frame that straddles the shock mounts.



Through the center of the “U” runs a 5/8” all-thread rod. A thrust bearing separates a nut from the frame. On the bottom of the all-thread is bolted an eye. Two jacks were built.

I started by lifting the front of the engine. Using ” Dyneema rope, I lashed the eye to the engine mount, bolted to the engine. With both jacks in place, I proceeded to tighten the nuts, raising the engine, one inch per side. Going back and forth, with the help of some wooden blocking, I was able to lift the engine high enough to allow me to slide out the old, cracked mounts and slide in the new (being very careful to never allow my hand to get under the engine mount in case it were to let go and crush my hand).



With the forward mounts in place, I repeated the operation in the aft of the engine.



Also damaged was the flexible coupling which I must say, saved my transmission and for which I am very grateful.



The Cutless bearing was also way out of round and had to be replaced. For that I made a pulling tool which allowed me to extract it smoothly but that's a tale for another day.

All in all, the repair probably took me about 5 days from start to finish including the fabrication of the jacks. I can’t be too annoyed with my friend as he bought all the replacement mounts, flexible coupling and Cutless Bearing and I secretly enjoyed the project.
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Old 29-11-2019, 21:10   #2
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Re: Custom Jacks for Replacement of Engine Mounts

Nice work with the jacks!

Your friend dogged a bullet....
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Old 29-11-2019, 22:54   #3
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Re: Custom Jacks for Replacement of Engine Mounts

Good solution, glad your friendship survived it as well as the boat...
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