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Engine Mount Confusion

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  #1  
Old 08-16-2018, 06:21 PM
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Default Engine Mount Confusion
The rear of the engine (via the trans) mounts to the pivot arm. Why the rear isolator?
 
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Old 08-16-2018, 07:19 PM
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It's gotta attach to the frame somehow...maybe I don't understand your question.
 
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Old 08-16-2018, 07:32 PM
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It attaches to the frame via the transmission. The rear isolator doesn't support the engine like the front isolator does.
 
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Old 08-16-2018, 08:41 PM
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The swingarm is attached to the tranny case as you noted. The isolator is attached to the back of the tranny case and to a plate that is welded between the Dyna's rear "downtubes."
~
 
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Old 08-16-2018, 08:44 PM
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Exactly. I don't understand the design concept. Essentially, the rear of the engine is hard-mounted. Why the isolator?
 
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Old 08-16-2018, 08:54 PM
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Actually it doesn’t, go back and read a few of tincupchalice’s posts on the subject. The swing arm is connected to the transmission, it doesn’t touch the frame.

The only connection to the frame is the top shock mounts.

Think in in terms of sections. The frame is one section and the power train another...

The frame includes the front forks, front wheel, gas tank, rear struts & rear fender and all that is attached.

The power train would be the motor, transmission & rear swing arm and everything attached to those items including the exhaust.

The reason for the rear rubber mount, is to help the power train. If it was ridged it would be breaking transmission cases.

The reason the FXR handled so much better was that the swingarm was part of the frame, not the power train....
 
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Old 08-16-2018, 09:59 PM
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Went out and looked at it again. I see that the swingarm pivot bar is only attached to the transmission and not welded to the rear downtubes. Hmmmm. So the connection to the frame at the rear of the engine is the isolator. Hmmmm.
 
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Old 08-16-2018, 10:07 PM
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Originally Posted by Huggerbugger
Went out and looked at it again. I see that the swingarm pivot bar is only attached to the transmission and not welded to the rear downtubes. Hmmmm. So the connection to the frame at the rear of the engine is the isolator. Hmmmm.
Bingo.

And hence: Alignment... Stabilizer... etc.
 
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Old 08-17-2018, 10:13 AM
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Originally Posted by Huggerbugger
Went out and looked at it again. I see that the swingarm pivot bar is only attached to the transmission and not welded to the rear downtubes. Hmmmm. So the connection to the frame at the rear of the engine is the isolator. Hmmmm.
Yup. Not a great performance solution. Kinda like building a house on a foundation made of gelatin. They tried to limit lateral movement with the design of the isolators but it's less than ideal.
 
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Old 08-17-2018, 11:17 AM
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I guess I'm just not comprehending the design philosophy. Even my expert Indy did a double-take when he first saw it. Why would you attach the engine to the swing-arm?
 
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