frame alingment

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Looking in the repair manual it would appear that the bottom frame rails,rear seat hoop and through center of the rear iso and Z plate hole should all run parallel,does any one know if this is correct.If so is the rear iso the best place to aling the rest of the frame to, treating it as a rear swing arm mount.On a quick check I have 3mm diference between front and rear iso mounts,so I know something isn't straight. In another post it is suggested that the rear swing arm is offset to the frame,is it the cradle and swing arm that is offset and not the frame.I was going to use a long bar through the steering head and then bars through front and rear iso's and shock mounts that should give me enough reference points,unless some one has a better suggestion.I was quoted about two weeks wages just to get the frame checked on some flash machine so I would rather check myself. :roll: :roll:
 

L.A.B.

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splatt said:
In another post it is suggested that the rear swing arm is offset to the frame,is it the cradle and swing arm that is offset and not the frame.

As I understand it from our previous discussions on this subject, from what I've read elsewhere, and also from my own observations and basic measurements, that the frame would appear to be symmetrical, the cradle sits offset to the left of centre within the frame by *approximately* 3/16", and the swinging arm is slightly asymmetrical in that the right side arm splays out slightly more than the left, and therefore compensates for the cradle offset, resulting in the arm's axle plates and, more importantly, placing the shocks' lower mountings equidistant from the frame centre line otherwise the shocks would not be set vertically?
The rear wheel rim offset as far as I'm aware, should logically be set on the frame's centre line, and not centralised within the swinging arm.
 
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bpatton said:
It's interesting reading but you need to take it with a grain of salt.
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I agree, very interesting reading but totally unreasonable to be working to those sort of tollerances on a road vehicle, a couple of thou in a wheel bearing would render all that precision totally useless. Splitting hairs comes to mind !
 
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daveparry said:
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I agree, very interesting reading but totally unreasonable to be working to those sort of tollerances on a road vehicle, a couple of thou in a wheel bearing would render all that precision totally useless. Splitting hairs comes to mind !
It's true, but it gets worse. The Commando frame is so laterally flexible that it's silly to knock your self out too much on this. DAMHIK.
 
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I bet they enjoyed themselves and certainly have bragging rights. A stock Commando frame served me well for many years though.
 
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As I dont have the means to measure that acurately,tape measure,ruler,rafter square and large verneirs I was hoping to try and get to about 1/2 to 1mm better if I could ,but I have to be realistic with the tools at my disposal .Back to my original question,does any body know if the top seat rail,bottom frame rails and the rear iso and Z plate bolt center lines should be parallel :?: :?: . My bikes get ridden hard with modern rubber so I would like to get it as straight as I can.
 
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Splatt,
You're right, both the seat rail and the bottom frame rails are parallel with the plate that forms the rear iso. But you can't use them as reference points, especially the seat rail. They just aren't reliable. Is the frame stripped? When you said there was a 3mm difference between he front and rear iso's, what did you mean? You can buy 1/2" drill rod in 3ft lemgths for under 5$. The are very handy to check the relationship of the front and rear iso mounts, by distance and with a level. Depending on whether you think it's fun, you can copy what Stevan did. It's amazing what you can do with a length of 7/8" oak doweling and a solid cored door, or similarly flat surface. Your tolerances won't be in thou's but that's fine. The question becomes what to do with the data you get.
 
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I was hoping to realign the seat rails back to the iso plate,not the other way around. The 3mm difference is from one side of iso mounts to the other. Thats about what I want to do 1/2 '' rod long bar through steering head and a friend with an automotive chassis straightening jig. We will either fix it or *(^&% it. :shock: :shock:
 
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