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Old 03-25-2013, 12:49 PM   #792
Gnarly Adventurer
Joined: Oct 2010
Location: NYC
Oddometer: 185
While I'm still waiting on some output sprocket parts from Christini focus was changed to the headstock gearbox assembly. Since I don't want to weld on the replacement headstock we need to accurately measure the new bearing spacing so that the bevel drive input gear is properly located.

After some careful measuring and machining of the existing parts I was able to fit the standard KTM head bearings and seals. This setup is merely to allow for alignment checks and smooth operation and all of the internal headstock parts will be remade without shims and spacers.

Now I can fit the new triple clamp assembly into the headstock to verify locations and alignment.


Now knowing that it all actually fits together I need to determine the location of the input shaft relative to the steering bearing seat. This is crucial because the frame needs to be drilled and a bearing support installed and if done in the wrong location would mean a noisy gearbox at best and at worst a non-functioning gearbox.

To do this i needed to make a test headstock where I could machine the input shaft in its likely position and then shim the steering bearings until I got a proper gear mesh. Once done shimming I know exactly where everything needs to be. All of the relevant surfaces were machined so getting accurate measurements should be easy.

I started with a block of aluminum held in a vice in the 4 axis mill.

In several operations I machined the input and headstock bearing bores and a couple of inspection windows to allow for direct backlash measurement.



With the assembly test fixture done its time for a test assembly.



With a few thousandths of shimming I was able to get excellent gear mesh.

Now that I have all the many components done I need to make a drilling/welding fixture for the actual frame modifications.

It will look something like this and allow me to drill out the access hole, machine a bearing support for a tight fit into the hole, and then hold it in proper alignment for welding. Getting as snug a fit in the drilled hole as possible will eliminate any distortion due to gaps in the fitup.

I should get the sprocket parts this week which will allow me to finalize the idler gear shaft centers and start to draw up some chain support and housing parts.

Once that is done it will be time to start molesting the frame in earnest.
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