This has been a long saga, full of woe.

I sheared two of the manifold bolts, and tried drilling them out in the frame. I got one out, but the other (outer bolt) was hard to get at, and I accidentally ended up drilling into the cylinder head.

I removed the cylinder head from the bike, removed the remainder of the bolt, and was horrified to realize I drilled into the passage above that hole. It is plugged on the size of the cylinder head by the larger allen bolt (#8 in the diagram http://www.bikebandit.com/2008-suzuki-gs500f/o/m17395#sch554402).

So now I'm left with 2 shoddy manifold bolt holes. They have enough thread left in them to do their job, but the one is now permanently connected to the oil passage.

Should I just cut the crap and start shopping for a new cylinder head? Or is there a prayer that thread sealant will be able to handle it.

It's worth a shot. In my limited experience, any time you try to fix something that used to be metal with sealant, JB Weld, etc. it just doesn't hold up. That said there are a lot of old really impressive mechanic tricks out there that with blow your mind. I recently found a video on youtube of a guy removing a pilot bearing with an old bolt, a hammer and some pieces of bread. Not that that's useful in this situation.

guess it depends on how much time you're willing to put in on something that might not work. If you can give it a quick try with some internet searching and cheap product you don't have much to lose. Try something really elaborate and you may be back at square one and a whole lot more frustrated.

I recently had to replace a gas tank b/c I realized that the one on the bike I'd bought was full of horrible sealant that was gunking up the carbs. I spent countless hours and well over a hundred dollars trying to clean the inside of the tank with strong solvents and acid. I ruined the paint job on the tank in the process and set out to repaint it and after sanding the bad spot down took a step back long enough to realize I could easily spend more countless hours and dollars trying to repaint the thing just to have it look like garbage. So, I just searched the web for a used tank for 8 months until I found one wishing I'd done that in the first place!

I had something similar happen. Bought a new complete exhaust system and could NOT get the OEM headers off. Stupid cheap metal allen bolts rounded off and were seized since the cyl. head is aluminum.

Plan was to drill out and helicoil. I stupidly used a hand drill and one of the holes was drilled off center so the new header clamps wouldn't line up.

You have the head off so do this first:

Take it to a machine shop. Explain what happened. Aluminum doesn't have many options, but you never know what they can do for you.

If that doesn't work, buy a new cylinder head off ebay. Don't pay more than $175 for one, regardless of years or miles.

Thanks you two.

If I do decide to go with a new (used) cylinder head, will I have any problems with fitting (valve seals, etc) or is it simply transfer over everything from the old head and I'm good?

As long as the new head is complete and functional its a direct swap. Get the Haynes manual and it will describe how to install.

You will need a new cylinder head gasket, new copper washers for the dome nuts, and new washers that go on the long bolts between the cylinder and cylinder head. In other words replace anything that wasn't a bolt when you removed the head.

If you reuse the old camshafts then you will probably have washers that go along with it. These washers keep the camshaft from shimmying side to side. There shouldn't be any play as long as the camshafts can spin freely. Make sure you use assembly lube on the camshafts since the new cylinder head will come cleaned.

Remember to keep tension on the cam chain so it doesn't slip off the crankshaft during assembly.

Let us know when you are ready to do the install and we can guide you through it.

Another thing. If your bike has an electronic tachometer, make sure you buy a new head that also has an electronic tach. The older GS had a mechanical tach cable and there is a hole on the front of the head where it screws in. On newer heads, there is a dimple where this hole would be but its filled in. 

Thanks for the in depth answer.

I'm gonna follow your advice and bring it to a machine shop first, to see what they say. I'm thinking if I can get a piece of round bar stock welded in the bolt hole, so its flush with the exhaust port (essentially filling in the hole) then it could be drilled and tapped for a smaller shorter bolt size, perhaps M5 instead of M8.

I think this would work, as the weld would seal the inside area from the outside (ideally). The oil in that passage that is now connected to the manifold bolt hole is stagnant, to the best of my knowledge, so I'm not worried about that passage having a little more volume.