Last weekend I went up to my brother's and did another session on the Horex and the roller coaster of emotions continues.  On the one hand, there are many beautiful and impressive aspects to it; on the other hand, every time I take something apart on it I find something broken or bodged.
The first thing I did was pull off the wheels to mount the new Heidenau tires I got from Ivan Messina's Motorrad Unlimited.  I got a 3.25 X 18 K34 for the front and a 3.50 X 18 K36 for the rear.  The wheels are impressively light, the front weighing only 13 lbs.  They have alloy rims, quite wide WM-3 front and rear.  I don't know if Horex made the rims themselves, but they're unlike any of the Italian, Spanish, British, or Japanese alloy rims I'm aware of, having a lower shoulder.  And, the axles are beefy at 18mm diameter.  When I took off the rear wheel, I realized it was missing the rear axle adjuster on the left side.  I've located one in Holland, but a 22 euro plus shipping, I may well fabricate one.  Then I struggled to separate the rear sprocket, cush drive, and hub.  It looks like it threw a chain once and pieces were distorted.  Then I found it was missing one of the brake shoe return springs and the tit on the one shoe that the spring hooks on was broken off.  This is on the fixed pivot end of the shoe, so it isn't nearly as important as the one at the cam end, but it's one more item on 'the list'. I shortened the front brake cable for the lower handlebar I had installed.  In the rear, the stop for the brake pedal was bent so it wasn't doing anything.  When I straightened this and got the pedal in a reasonable position, I found I had to relocate the brake light switch so it wasn't on all the time.

There are a number of beautiful aluminum castings on the bike and the one that fixes the rear backing plate to the tang on the swing arm is an example.  The shift and brake pedals another.  On most bikes of the era, they would be steel.  These lightweight aluminum castings seemed to allow them to overbuild other features,  like the axles, and end up with a bike of comparable weight.
Next, I removed left engine cover to remove the original charging system and ignition.  This involved removing the shift lever, kickstart lever and footrests.  The stud the footrest mount on was very bent and I had to pound it out, straighten it, and chase the threads.  The Powerdynamo alternator/ignition uses Czech VAPE components mounted on an aluminum plate made specifically for the Horex.

It's a 12 volt, 150 alternator with a pointless electronic ignition.  They have you remove the original Woodruff key and mount the rotor on the crank taper without a key.  So, you have to mount a degree wheel and zero it, then turn the crankshaft to the proper advance ignition point, 43 degree BTDC in this case.

Then remove the degree wheel and put the rotor on in the correct relationship to the stator.  I found when I tightened the rotor bolt, the crank moved.  So I removed the timing side engine cover to find some way to hold the crank while I tightened the rotor bolt.  That's when I found the primary chain was incredibly loose.  There's a threaded adjuster that comes through the bottom of the right crankcase that bears against a nylon slipper to tension the chain.

When I screwed this in, it went way past the point where the lock nut could grab it and the chain was still slack.  There is either and intermediate piece that is missing (unlikely) or this threaded adjuster has be broken off and ground shorter (more likely).  Add another item to 'the list'.  I got the rotor mounted in the correct position, but have yet to mount the rectifier, voltage regulator, coil, and 'black box' in the tool box.
Brother Douglas had changed the muffler on his Benelli and offered me his old one for the Horex.  It looks pretty reasonable when I mocked it up and now I have to get a second one for the other side.

Also on 'the list' is mounting the Velo seat properly and trimming and mounting the front mudguard.  Ultimately, it's going to need a chain and sprockets too, but let's get it running first.