Motor mounts

[William Walter]

So I decided to change all my motor mounts on my 480ce.At first I thought it would be easier until I looked at my access and the amount I would have to jack up my engine.My shafts are out right now so the access would be better.The yard wants a ton to do the job so if it’s something I can tackle I would like to give it a try. I don’t want to bite off more than I can chew so I’m looking for advice from anyone who has done this.The boat is a 38 tiara open.Was wondering how high each corner has to go to get the new one in. I’m thinking loosen top bolts jack up as much as necessary to get new ones in.I’ve never actually aligned an engine so I imagine that would be a major undertaking after changing the mounts.Any advise appreciated.Bill

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[William Walter]

Thanks to all for the great information.Gene you’re right about formulating a plan. I looked at pictures of my engine room and as Rob said I have what looks like aluminum spacers under each mount and top nuts are pretty high on the stud.Hopefully the sliding sideways method works after getting the pressure off. I plan to measure the height before removal of each one to help with alignment.The new mounts look like a match to the old so hopefully if I thread it the same as where the old ones are that should get me close.Some of the old mounts are bottomed out hence the project.

[Gene Fuller]

I replaced the mounts on my QSB5.9-380 by myself, and I used the “raise til it clears” technique. I decided to avoid removing the brackets from the engine because access to some of the bolts would require removing other engine parts. There were no spacers or loose bracket holes to allow a small lift. I needed to lift at least 2 inches. The exhaust connection was removed but nothing else. (Good time to inspect the turbo.)

 

The most important part is the planning. It is impossible to lift one corner at a time with this approach, so a coordinated lift of the front two and then the rear two (or vice versa) is required. I slightly loosened the non-lifted pair when the other pair was lifted so that the engine could easily pivot on the loose bolts.

 

I made special screw-type lifting fixtures that were constrained and safe to avoid simple jacking to that height. Every boat will be different so I will not bother to detail my fixtures.

 

I spent a week pondering and planning, a day making fixtures, and two hours to complete the actual work.

 

The shaft and coupling alignment is an acquired skill. I will presume the coupling flanges are true and flat. If not, that needs to be corrected before anything else. The other preliminary step (often skipped) is that the shaft needs to be in the correct place. Lengthwise just make sure the prop is located at the correct distance from the final Cutless bearing. Probably the same place it was originally.

 

Laterally the shaft needs to be in the center of the forward-most bearing or shaft seal. My boat has two well-fitting Cutless bearings so the only thing I needed to do was put slight upward pressure on the shaft at the coupling to counterbalance the weight of the extended shaft and coupling. (I calculated the shaft sag to be about 25 to 30 thousandths)

 

The other trick for alignment is to use a thin spacer between the coupling faces when adjusting the engine position. I use a spring Pony clamp to lightly hold a 0.015 inch shim between the faces at one point on the perimeter. Then test the gap all around using feelers of about the same 0.015 thickness. Much, much easier than trying to figure out whether a flimsy paper-thin feeler gauge fits or not.

 

It helps to have good spatial sense to figure out how to move the engine to correct errors seen with the feeler gauges.

 

The final test is a complete absence of vibration. I did this entire operation twice (used sub-optimal mounts the first time) and was successful both times.

 

Gene

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JimmyK

[JimmyK]

By default I would be thinking loosen all 4 top nuts, jack up each corner one by one only a smidge-just enough to unload a single mount, remove bracket with each mount, put new mount in w/bracket, refasten everything.  Then move to the next mount and repeat.

Also, I would use a digital caliper and measure the position of each bottom nut relative to its stud and pre-set the bottom nut on each new mount to the same location before install.  this will get you fairly close and give you a head start on alignment.

Please document the whole thing here I’m sure some of us would like to learn from your experience.

[Rob Schepis]

Lots of variables as to how easy they will come out, or not.  If the mount is sitting on a spacer and the adjusting stud is somewhere towards the top half of the stud you should have to jack the engine only enough to support the weight and then the slop between the mount stud and the hole in the engine bracket should be just enough that you can get the mount sideways enough to slip it out.  If there are no spacers under the mount and she’s sitting lower on the stud that’s when things get interesting and you need to raise the engine more and possible remove the bracket from the engine.  Thinner welded steel flat stock engine mounts allow more wiggle of the stud than do thick cast brackets.  So in a nutshell – engine brackets that are slotted/thinner and mounts sitting on spacers are your friends …. all else lead to bloody knuckles and 4 letter words.

[Tony Athens]

Pictures, pictures and more picture.. No one here has a crystal ball to see what your are attempting to sort out.

Vibration Isolator & Engine Mount Views

 

 

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