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The last photo you published indicates a Mk 3 setup
What's up with my Z-plate / rear ISO
- Thread starter Tom P
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- Nov 20, 2004
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Yes, it looks like a Mk3 length (either Mk3 or shortened original) mounting.
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- Sep 22, 2015
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The primary case moves. Have you checked your primary chain? The gap may or may not be related to your handling. I'd check the isolastics, then the shocks, then the wheels (alignment and spoke tension)
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- Aug 7, 2021
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The primary chain is fine, maybe a touch slack. There is no problem with the handling at all, just a bit of vibes mainly through the left footpeg
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- Oct 28, 2009
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I wonder if the frame is bent, forcing the front isolastics towards the rear.
This could be checked using the frame dimension drawing, found here:
www.accessnorton.com
The engine and cradle establish a fixed length between the front and rear isolastics. But if the front of the frame was bent rearwards, it could load up the isolastics, reducing the space around the zplate as per your photo.
One way to check this would be to take the weight off the engine and pull the front isolastic bolt, then see if the front holes remained lined up. If they don't, this could begin to explain your problem.
This could be checked using the frame dimension drawing, found here:
Dimension blueprints of frames, parts etc?
Looking to draw up the bike in solidworks for additional design ideas/modifications. Since the bike is 40 years old, do blueprints exist? Ive seen the simple dimensional drawings from the work manuals, but they look to be for checking the frame positions, I was hoping for alittle more. I have...
www.accessnorton.com
One way to check this would be to take the weight off the engine and pull the front isolastic bolt, then see if the front holes remained lined up. If they don't, this could begin to explain your problem.
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- Sep 22, 2015
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What was i saying ??? No, the primary case does not move, only the sealing disk moves. Surprised nobody called me out on that. I agree with Stephen, if the primary case doesn't move, then there's an issue with either the location of the primary case or the z-plate. The primary case is located by the cradle (via the primary case stud) and the crankcase which is connected to the frame via the front iso. A bent front frame affecting the front iso could be a cause, or it could be the z-plate out of alignment at the rear iso tab, i.e. a bent frame somewhere that's affecting that?
You had it sort of right before, the primary case does move around in relation to the z plate. It has nothing to do with the primary chain tension ,however. That just pulls on the two sprockets or pulleys and might yank the trans forward if too tight.
The z plate is mounted to the frame ( not supposed to vibrate- much) The primary case is mounted to the engine and cradle (vibrates a lot!)
As mentioned in post 7 and again later, the small or nonexistent gap in the photo does seem like it would most likely be caused by a bent frame.
I'm not sure what else would cause that.
Some frame measuring is in order.
Glen
The z plate is mounted to the frame ( not supposed to vibrate- much) The primary case is mounted to the engine and cradle (vibrates a lot!)
As mentioned in post 7 and again later, the small or nonexistent gap in the photo does seem like it would most likely be caused by a bent frame.
I'm not sure what else would cause that.
Some frame measuring is in order.
Glen
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- Aug 7, 2021
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Well, I jacked up the engine, to support the weight, and removed the front Iso bolt, the mounting holes in the frame were in good condition (not oval) and the iso tube did not shift, the bolt went back in with no problem. I checked the front down tubes with a straight edge, they appeared to be straight, Had a good look at the steering head, down tubes, top tube - no evidence of distortion. I will need to machine up some long rods to stick in the frame lugs for the iso's so I can measure to see if it is in spec. Do the engine mounting holes in the crankcase hog out on commandos? I dont know, so thats another thing to check.
baz
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Yes the crankcase holes do hog out but they'd have to be really bad to give the symptoms you have
Still worth checking though
maylar
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Yes, especially if the shims on the inner primary are left off. In extreme cases the crankcase can crack around the mounting holes, as mine did -
The resulting engine movement would be in the direction that you are experiencing. Another symptom of this is that the left swingarm pivot digs into the back of the primary.
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- Nov 4, 2007
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And your Z plates ? I know it is a bit a bodge but instead of the 3/8 bolts (two on each side ) try 5/16, thus the z plates could rotate a bit around the rear iso stud and increase your gap , as you see in your pic the gap is ok at iso rear stud but going thinner then after down ........................;
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