MarinS4

Best of luck Tialoc, sound like you got a solid plan.

With regard to the subframe bolts. I have found them to be stretch bolts in all auto sub frame applications. This was confirmed when I had to R&R the rennline solid mounts. I called them and they confirmed they were one use bolts. I changed em out even though I never even put the wheels on. When you torque em up they do feel stressed.

Cupcar

You may want to use Cobalt drill bits. Also if you can drill the entire length of the retained bolt that sometimes relieves some stress holding it in place.

Tlaloc75

Yes thank you. I have a cobalt bit in 1/4 and 3/8 now and will be drilling the 1/4 all the way through as my next step. I'm about 3/4 of the way through the bolt already so just a bit more and it'll come through.

I was able to eyeball the top of the hole btw. If you look in your engine bay, left side, you can see a small protrusion about 6 inches back from the shock tower. This is the top of the threaded hole as far as I can see. Its closed off, but available if needed and definitely shaped in such a way that the bolt can't completely bottom out.

Figured I'd share in case that information is useful to anyone else.

MarinS4

I was just thinking a reverse drill bit would be ideal for this application. As it catches and binds it will loosen the bolt rather than tighten it.

Google and amazon show results for reverse cobalt drill bits.

Tlaloc75

I have been using both reverse and standard bits with the idea that it wouldn't hurt to try to budge it in both directions. So far the bit has cut well but hasn't exerted much twisting force to speak of on the bolt, so it hasn't really mattered. Maybe that will change once it breaks through the other side and has something more to grab onto.

JasonAndreas

Even with cutting fluid you should forget about titanium and cobalt drill bits unless you also plan to buy a drill doctor... The suspension bolts will eat them up, especially with a battery operated hand drill. Head to your nearest Ace Hardware store and pickup an "Artu" tungsten-carbide drill bit and some "Magic" tapping fluid. The combination will go through ANY fastener on the 993 in a minute or less.

Tlaloc75

Like this? http://www.acehardware.com/product/i...ductId=1444716

I do shop at ace, that's where I've picked up my bits so far.

I've been using this:
http://www.acehardware.com/product/i...393177.1259483

And this:
http://www.acehardware.com/product/i...uctId=90189526

Vandit

Not that this helps OPs situation but can we clarify some things for future use...

-Are the subframe bolts really one-time use "stretch" bolts?

-was torquing one side of the subframe before starting the bolts on the other side of the subframe a bad practice? I'm not familiar with 993 subframes, but I would assume you start all bolts and get them all the way down and hand tight way before you bring out the torque wrench to crank em to spec...

- what is the appropriate torque value for these fasteners? OP said 120NM if I recall page 1 correctly. That's what, approx 80ft/lbs?

Tlaloc75

I can answer these based on what I've found out:
1) Just talked to someone else in Sonnen parts. He stated that these are not stretch bolts but that when doing this repair they would always replace them for safety reasons. This goes for all of the bolts that attach the subframe to the car. He said that not everyone does it but at the dealership they always do. Looks like I have another hardware order to make.
2) My bad assumption was that the main subframe bolts would locate the subframe precisely on the car and therefore everything would line up. Following this line of reasoning it made sense to tighten so that things lined up exactly as needed. What I didn't realize, till too late, is that there is room on this fitting for the subframe to move around before tightening so you need to only partly tighten, align everything and then tighten fully.
3) All of the M12 bolts are 120nm and the M10 are 80nm as far as I can tell. Its not in the Bentley manual so I used Jackal's description of this repair as my source.

I think my M12 was tightened beyond 120 since I gave it a little bump past the torque wrench click. Whether this played a part in the problem or not I'm not sure. I would expect the safety margin on these bolts would be quite high and so a little extra torque shouldn't damage the threads, but.... here I am.

Cupcar

Just don't break it...drilling with a Tungsten- Carbide, hand held going up...

Tlaloc75

That's my goal! Which of these bits do you think is least likely to break?

I haven't felt any undue torque or felt a danger of breaking yet, but that could change quickly as soon as I bust through the other side of the bolt.

NC TRACKRAT

Suggestion: Since you can see the top of the threaded hole, get some KROIL or PB Blaster and, using a long extension tube, squirt the liquid on it. Also, when in stressful situations, do what an old friend of mine suggested: "Practice your breathing".

Tlaloc75

I can see the top but its closed off and I'm not at the point that I'd want to cut that open. As soon as the bolt is drilled through I will spray some triflow up through that hole and allow it to drain down over the threads.

Tlaloc75

Here are the part numbers for all of the nuts and bolts that hold the subframe to the car.
- The lock nuts that attach subframe to car
- The bolts that hold subframe onto car

What do you guys think about bolts for the control arms, should they be replaced? I bought new nuts but have been planning on reusing the existing bolts.

Tlaloc75

Quick update - I talked to Sonnen again and they stated that the control arm bolts are fine to reuse. They are not torque to yield and they do not typically get damaged. The subframe bolts are more likely to be damaged and that's why they recommend that they are replaced.

Edited: I talked to someone else at Sonnen and they gave me different information. Stated that the bolts should be replaced and that even though the manual doesn't state they are torque to yield they believe they are. So to be on the safe side, I would assume these are stretch bolts and they do need to be replaced every time.