Ouch. That's gonna suck.

Those bolts (and the bolts for the starter) are long and thin and don't take kindly to excessive torque. I put anti-seize on everything.

Oil filter bolts... Obviously soak it in good penetrating oil. I'd start with a flat bottomed carbide burr for a dremel and try to flatten the end of the bolt. That will help the drill bit not walk around while trying to drill the bolt. Then drill it for an EZ out. That will take a VERY steady hand. Go real slow. A drill guide might also help.

You might try using a manual impact driver with the EZ out as the hammering may help break it loose. Laying the bike on it's side might help as well. Drilling vertically is easier than horizontally.

Some of the boys have done this, I haven't, they'll help you out.

For the one that's broke off deep inside, I'd guess a bit of a jig using a piece of rod exact dia with a hole drilled down centre of it, have to be spot on accurate, like made in a lathe if you got a chum in Engineering.

Need to ensure no swarf from the drilling gets lost internally.

Here's a video that demonstrates techniques for Removing Broken Bolts. Watch, listen and learn. Best of luck with this..

The situation is the engine case is soft aluminum and the bolts are steel. I'm also not sure if the holes are blind which means you don't want to drill through the engine case. You'll need to know the depth of the hole. Perhaps someone here can back out their bolts and provide a depth measurement. Something to use as a not to exceed drill depth.

You'll need to make a guide for the drill as hand holding it is out of the question. I'd make the guide no less than an inch to hold the drill. This can be made from steel rod or square stock. The next challenge is finding a way to fix the guide so it's centered over the female threads. I think they would be 6mm x 1 but someone needs to verify that. The tap drill for 75% thread is either a 5mm or #9 size.

Facing off the cross section of the broken screw will prevent a drill from walking off center. If you can drill the hole out with a tap drill you can "chase" the threads with a spiral tap. As most of the screw metal will be gone. There are taps that have a drill point. One of these may be of value to get a centered starting point. You'll need to be careful not to tear out good threads. And also that there are enough threads to secure the tap. Caution advised.

The other approach is to drill for an easy out. This might be a good first attempt. If the easy out drill hole is centered you can tap drill it later if the easy out fails to remove the broken screw.

Heat applied to the engine case may help loosen the screw. As a last resort, you can do a helicoil thread repair. Any of the above requires a centered drill hole through the screw. Any and all efforts should be made to accomplish this as it leaves the door open to options. If the drill runs off center and starts to drill away the aluminum that will be a bad scene. And once that starts it's very difficult to correct.

As a general rule, I'd never torque bolts for a cover like that. Just a little snug is always good enough. If a bolt loosens the worst that can happen is you'll leak a bit of oil. Far less serious than a snapped off screw.

Good luck with the repair.

Update:
I was able to get the little screw off by lining up a drill bit with a centerpunch. I couldn't get into where the bigger bolt was though and took off the crank case cover. Once removed, it was easy enough to centerpunch the other screw I then had line of sight on and drilled it out as well. Neither bolt needed an easy out. They came out with the drill bit.

So now I have a new gasket ordered and will wait for that to come in.

All told, this oil change has cost me around $110 in tools and parts. haha

Well done that man, takes some skill & a bit of luck to get them out without damage to the ally.

Good on ya for solving the problem, and welcome to the "Woops, I Shouldn't Have Done That Club"!

How many times over the years I've leaped into something before looking it over carefully and cost myself time and money trying to 'fix' a situation of my own creation I can't say. Do my best to avoid such mistakes, but even rocket scientists get it disastrously wrong on occasion, so our club members include some of the best!

Glad you got the screws out. Good job so now you can move forward. Ride safely.

quaziau, you got me motivated. I like to change my oil & filter every 600'ish miles (1,000km's) but last time out I got home cold, tired & lazy. So this morning after reading your post, I got multiple layers on & set off to warm her up for a service. out at 10.30am 2°c after 77 miles in sunshine but low sun in my eyes half the time. Back at 3.15pm into my garage at 5°c, like a sauna eh. Anyway got amongst it, nice clean oil & new filter, Lubly jubly. Just a tad over normal at 681 miles.

Cheers m8.

Wow, I'm glad it was easier than expected. An expensive oil change for sure, but I still think you got off easy.