x758 motor mount issues
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    6shooter's Avatar
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    x758 motor mount issues

    I've been noticing in the cold weather when my machine takes a bit more cranking to take off, it really gets the hood flopping around after a few seconds and the motor starts to take off. It's gotten progressively worse, so I decided to pop the hood and investigate. I've got at least a 1/16" between the top of my rubber mount and the large washer. None of the motor mount rubbers are split or failing, but every one has this gap that I know shouldn't be there. I can pry up on the mount plate lightly and move my engine up and down almost a full inch before the rubber gives any substantial resistance. Going to call the dealership and see what gives, it's still under warranty, only has 125 hours on it. Anyone else notice their motor mounts are compressing and not holding tight anymore?

    Left rear mount;



    Right front mount;


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    TJR345's Avatar
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    Well being under warranty says it all and what I would do is talk to the dealer and see if they have one there that's the same way.A cold diesel will shake some starting cold.Try cycling the glow plugs twice before starting to see if that helps.When I have to start mine in the cold I remove the air filter cover and use a hair dryer to warm the air before starting.
    Tom

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    56FordGuy's Avatar
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    That could be as simple as the nuts backing off and allowing the bolts to move in the mounts.
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    Keeper of the GTT Cookies dieselshadow's Avatar
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    That gap is normal. Here is a 455 with the same style of mount. As long as the bolt is tight and the elastomer isn't broken, it's ok.

    Click image for larger version. 

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    6shooter's Avatar
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    I called the dealer and the new x758 on their floor was the same way. I just can't believe a motor mount dampener is supposed to loose between the two mount surfaces. Mechanically, that makes no sense to me, and I'm a diesel mechanic. The vibrations of the engine will have to take up that gap (basically flop around between surfaces) before the rubber does what it's supposed to and dampen the vibrations. Bolts are tight on the spacer, I'm going to remove them and shave 3/16-1/4" off the spacers so the rubber is actually doing something.

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    Keeper of the GTT Cookies dieselshadow's Avatar
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    I wouldn't do that. The mounts move quite a bit while the engine is running. That space is occupied by the mount as it moves. Run the engine at varying speeds and watch them. You'll see what I mean. They are quite effective at what they do. If you cut them down, I'll guarantee you'll have a lot more vibrations.
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    6shooter's Avatar
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    In all my years of being a diesel mechanic, I've never seen a rubber engine mount that was purposefully sloppy. There is always tension, some small clamping force applied to the rubber isolators so the mounts don't hammer between the two parts. As long as they aren't smushed down so tight they're ready to blow apart, there's plenty of rubber there to take up the little bit of vibration that motor puts out. I watched the mounts as I turned the engine over and while it was running, the mounts barely even vibrated while running, yet my whole tractor shakes violently enough to see the hood gap at my dash open and close significantly while just turning the engine over. My old man is a machinist, I'll have him make me some shorter spacers, then I'll swap them out and see how it runs. If it vibrates too much, I'll just put the regular ones back in. That gap just doesn't make sense to me. If anything, a thicker top piece of rubber would be the proper fix, not leaving a gap for the mounts to hammer around in.

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    tj1
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    Quote Originally Posted by 6shooter View Post
    In all my years of being a diesel mechanic, I've never seen a rubber engine mount that was purposefully sloppy. There is always tension, some small clamping force applied to the rubber isolators so the mounts don't hammer between the two parts. As long as they aren't smushed down so tight they're ready to blow apart, there's plenty of rubber there to take up the little bit of vibration that motor puts out. I watched the mounts as I turned the engine over and while it was running, the mounts barely even vibrated while running, yet my whole tractor shakes violently enough to see the hood gap at my dash open and close significantly while just turning the engine over. My old man is a machinist, I'll have him make me some shorter spacers, then I'll swap them out and see how it runs. If it vibrates too much, I'll just put the regular ones back in. That gap just doesn't make sense to me. If anything, a thicker top piece of rubber would be the proper fix, not leaving a gap for the mounts to hammer around in.
    I am sure JD did this on purpose. If you do fool with the mounts you may do damage to something else under the hood and then there goes your warrantee.. I would listen to the Shadow because the Shadow knows... I Understand what you see with larger motors for sure but there has to be a difference in being the size of the motor vs weight and what else will that tightness shake?. It will transfer everything in the motor to the frame etc. You can give it a try but I know for one I would not. Remember if you break something you will be screwed especially with such low hours on the warrantee. Just my .02
    Jeff

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    6shooter's Avatar
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    My warranty is up next month anyway. They aren't going to do anything about them since the new ones are the same design. This wouldn't be the first time I've "improved" a poor factory design. If you think about it, the only time that space is taken up and the mounts are hammered between their two mating surfaces is during cranking and takeoff. I can slide a regular washer in between the rubber and metal when the engine is running, so the only time all that space is used is in the 2-3 seconds the machine is being started. Can't hurt to try it. As long as I'm not mashing the rubber down to the point it's unable to compress and dampen vibration, it shouldn't hurt anything.

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    tj1
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    Quote Originally Posted by 6shooter View Post
    My warranty is up next month anyway. They aren't going to do anything about them since the new ones are the same design. This wouldn't be the first time I've "improved" a poor factory design. If you think about it, the only time that space is taken up and the mounts are hammered between their two mating surfaces is during cranking and takeoff. I can slide a regular washer in between the rubber and metal when the engine is running, so the only time all that space is used is in the 2-3 seconds the machine is being started. Can't hurt to try it. As long as I'm not mashing the rubber down to the point it's unable to compress and dampen vibration, it shouldn't hurt anything.
    Well with the warrantee that close, give it a try, let us know what you find out. If it works for you, you may have a patent on your hands for a new aftermarket rubber mount that fits.. You could be our newest millionaire outside of Giz.
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    Jeff

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