Ikarus, yes you should have a service manual.  Even for the simplest repairs and maintenance, a service manual is a "must have" tool.

To do the repair I describe, or to install a heli-coil as Dave suggested, you must remove the head cover, camshaft, and cylinder head.  Either repair requires drilling and the metal chips will need to be cleaned out.  In addition, you need to block off the oil passage in the cylinder to keep the chips from goin down the chute.  It's a fair-sized job but well worth the effort.

The heli-coil looks cleaner and maintains the stock design; the through-bolt & nut is stronger.  The heli-coil requires the kit with special tap, drill bit, insertion tool, and inserts; the through-bolt & nut requires the long grade-8 bolt, acorn nut, long 1/4" drill bit, and the valve seat cutting tool.  Either repair is good.  I prefer the through-bolt for the added strength and ease of future repair.

Moarpower, does this reply answer your question.

There's some serious mecha-nicking going on here! Nice to have all these free design workarounds at our disposal.
Thanks to many of you.

You need to take it apart to fix it.

"Thus, 133-128.5 = it catches 4.5mm of thread, which might just be enough."

You won't have 4.5mm of thread because you can't allow the end of the bolt to bottom in the blind hole.  If you let the bolt bottom you will most certainly jack-out the remaining threads.  So, at best you will have maybe 4.0mm of thread engagement.  That's a steel bolt in aluminum internal threads.

The general rule for thread engagement is a minimum of one bolt diameter.  So, a 6mm bolt needs at least 6mm of thread engagement.  But that general rule assumes external and internal threads of the same material (steel bolt in steel internal threads).  You have aluminum internal threads and I suspect the mechanical properties of that aluminum don't even approach 50% of the grade 10.8 metric flange head bolt.

Your bolt and bolt hole are an integral part of your lubrication system.  This is a bad idea.  You need to take the cylinder head off and fix it correctly.

Congratulations.  I guess there's more than one way to skin a cat.  

Keep us posted on how it works out.  This whole mess started with a clutch problem, and then seemed to sort of spiral out of control.  So, how is the clutch working now?

No updates in a long time, but I havent had the chance to ride the bike until today, and even then I only rode it for about a minute around my block. Here is the good, the bad, and the ugly.

The good is the rattling sound is gone, the engine sounds great, and pulls strong. The clutch is now working properly, no dragging, and neutral is easy to find with the engine on and off, no more sticking when shifting 1-2 and 2-1. The sealed head bolt did not leak, but I'll have to give it a longer ride to be truly sure.

The bad is 10 seconds into the ride I heard a vibrating nose that immediately amplified. This time it was easy to discover - I have replaced my timing inspection port plug with the DRZ plug, for ease if removal in the future as it uses a 10mm allen bolt vs a long flat slot on the stock plug. Turns out the new plug did not come with a gasket, and I forgot to swap in the old one, so the plug immediately loosened up. Very easy fix.




Here comes to ugly. I took off the plug to swap in the gasket, and keep in mind the plug is brand new with only 2 laps around my block. I looked inside the plug and there was a ton of metal shavings in it, and some shavings inside the port hole. I cleaned the shavings, took the bike for one more lap around the block, removed the plug and there were more shavings, but this time a lot less than the first time. I inspected the old plug, and there were no shavings in it whatsoever. There was no shavings inside the port hole when I removed the plug to set the engine to the TDC. Also, when I drained the oil to work on my clutch, I did not see any shavings in it either, therefore these are new shavings that got there within the 1 minute that I was riding the bike around my blocks.

The shavings are probably from me redrilling the head bolt that goes through an oil passage - and therefore I probably deserve what's coming for not taking the advice to do it the right way. I thought I blew most of them out, but I guess not. I'm very surprised how fast they made all over the engine, I imagine if I found them in the port hole, they are probably all over the engine as well. I'm also surprised that these shavings seemed to be dry, not covered in oil - almost if they got blown in there by air. Could they have got there when I was blowing them out with compressed air through the head bolt hole?

That being said, I will keep removing and inspecting the port plug during for the foreseeable future. Would it be a good idea to do a few oil changes with some cheaper oil ever 50 miles or so to try and get the shavings out?

I'm thinkin your alternator rotor bolt is rubbing on that new timing plug.  That assessment is based on the location of the chips, the fact that the chips are dry, and your fuzzy picture.  Can't tell for sure from the pic, but it sure looks like the bolt has been rubbin on the inside of the timing plug.  That plug has raised casting material on the inside face.  As I recall, the stock plug is flat.  Put the two plugs side by side and take a nice clear photo, then post the photo.