I have seen this done and there is nothing wrong with it at all, drill away.
From: Tim de Martino
Sent: Sep 30, 2010 4:46 PM
Subject: Re: [DucatiST] Engine bolt conversion
Thanks for the input. Like many other repair tasks on my bike, the hardest part is the initial thinking about it!Here is the reply sent from TPO parts when I asked them about the conversion;Hi again Tim,
My apologies for the late reply. Here is the procedure you need to
follow for drilling out your bike for the 12mm studs.
Drill bit: either 12.1mm, 12.2mm, or 31/64-inch. Do not use a bit
larger than those sizes.
A source of compressed air is handy for cleaning chips out of the drill
hole. If you don't have that you can use a thin metal rod and a rag.
Begin your work with the engine installed in the bike using the factory
bolts. The factory bolts should be tight.
Remove 1 of the factory bolts only. The other bolt will hold the engine
in place while you work.
Drill out the bolt hole from both sides. There is no need for cutting
lubricant, but it won't hurt to use it if you want to. The drilling is
easy because you are only enlarging the factory hole a little bit, not
drilling a fresh hole. The existing hole will guide the bit for you
making the job easier. Once you've drilled the hole from both sides,
blow out the chips with compressed air (or other method).
If you want to use a cutting lubricant then I would recommend that you
use a water-based one made specifically for this purpose. WD-40 is not
very effective for this purpose and it leaves behind a sticky residue
that attracts dirt. If you use WD-40 make sure you clean it up well,
otherwise you'll find road grime sticking to your Duc! Water-based
lubricants are nice becasue you can rinse them away with no sticky mess.
Install the new stud and torque it down.
Repeat the process for the second bolt/stud.
As I mentioned earlier, the only important detail is that you use the
correct size drill bit. Do not use anything larger than 31/64-inch. If
you do not have a suitable bit then please let me know and I will send