Don't you have the original bolt, damaged or not?

Plug the part number in RealOEM and this is what you'll get:
No. Description Supp. Qty From Up To Part Number Price Notes
05 Reduced-shaft bolt M12X1,5X116-8.8 2 33326760361 $2.27

The bolt is 116 mm-long, but only partially threaded (you can measure the length of the tread from the original bolt).
The real question is what is the length of the thread in the bolt hole, is it recessed, at what depth?

I'd be trying to look inside the hole and would be poking it with a measuring caliper to get answers to some of these questions.

Then perhaps you may find it more suitable to install a time-sert (M12.5x1.5, the longest one available, which is 30 mm) rather than using a larger diameter bolt.

 

well since it’s the bolt that stripped it and not a stud then this must be one of the rear mounts.
might consider drilling all the way through and doing a secured top mount if also concerned about mount cracking. you don’t have to go full VinceBar but something if that nature. where you put two longer bolts in from the top and secure up top with a wide plate.

 

The inserts tend to be really deep, and quite thick- walled. I'd use a helicoil, tho, just to avoid drilling TOO much out.
In theory, the rear subframe shouldn't be a regular maintenance item, and the insert is steel, not aluminum...
...and helicoils are self- binding.

t

 

Another option. Get a longer bolt, as the actual subframe mount has some material unthreaded. You can cut additional threads and use a longer bolt if you don't want to go all the way as Alex mentioned

 

I had to helicoil a Volvo ( about 35 years ago ). It did hold for the next 8 years I had the car. Not the most fun, but helicoil or timecert is likely the best fix. Look at it this way. Stripped is better than snapped off inside.

 

...but the absolute worst is getting the tap jammed in there, and having IT snap off...

t

 

Thanks everyone for your help! What Alex mentioned might be my plan as it seems easier. Just to make sure I’m understanding this clearly, you said I could drill all the way up past the threads there for able to put a bolt down through and a nut? I’m obviously guessing it involves cutting a part of the trunk but that is no issue.

 

I am also not to concerned about mount cracking with this method as the car doesn’t have any crack to begin with but it is also been all reinforced.

 

Just drilling through and for a longer bolt isn't enough - there is a cavity above the mounting block you want to eliminate, similarly to vincebar installation. Look at the installation instructions and videos carefully - there is a large section of the top metal sheet that is cut out. Then, a solid metal piece braced on both sides serves as a support for the top nut.

 

yeah but that large section exposed is for the large brace. not installing that brace you can access the top with a 2” diameter hole cutter/drill. yes, it’s a good point to bring up to anyone unknowing.
Active Autowerkes (which I posted almost two decades ago) use to just do these longer bolts from the top and large top washer on their SC E46s early on.

 

So I did some research into the Vince brace at least im pretty sure that’s what they call it. Looks like a lot of work to install one of those for what I am trying to accomplish. Sorry if I am misunderstanding this but I still feel drilling all the way up from the bottom into the trunk and putting a bolt down through would work maybe I’m just not understanding. Looking at the Vince brace install yes it is similar but they cut a larger portion out all I need is a small hole. Another thing is this method would work better as I just re installed the subframe a few months ago and really don’t wanna go through pulling it out again creating the option of just drilling through. I can tap it but being I would need to go through the bushing hole and then up in the threads I’d be worried with an extended tap it would snap off. Also could I drive the car still well I am thinking of a game plan? The car is a project car always has and gets driven probably only 700 miles a year I don’t beat on it and drive mostly through town. Would it be okay to drive without putting to much stress on the other 3 bolts? The bolt also doesn’t completely fall out it’s in there but it’s not fully compressed to the bushing if that makes sense. I can get a picture tomorrow if that helps anyone.

 

Also I know you can just do a bolt and nut as it could slip through the metal being a lot of tension in one spot but could I take a good thick size piece of steel and use that as my plate so there is a larger surface area for the weight to cover?

 

i would think so. as i mentioned before, the tuner Active Autowerkes who did super chargers for E46s did this very thing early in the BMW game. way before anyone had plates or braces.

 

AA Easy Subframe Reinforcement

Was looking at an old post and found that Activ3 had his rear subframe fixed in a different manner than the expensive Turner way. This would only be inexpensive with no welding as preventative procedure when the subframe hasn't broken all the way through. Although it might work with no welding...

www.e46fanatics.com

here’s my original thread and thinking back in 2006. Post #60 has better diagram. *understand this was early in the subframe cracking experience and not much info was out as it is now. so some ideas in thread may be outdated/incorrect.

 

That forum really helped thank you! After reading it it sounds like exactly the method I’m looking to perform so I’m going to do that method. Seems easy enough well also what it sounds like is it might give it a bit more reinforcement which what it sounds like in the thread that the rear points are more prone to cracking and tearing unlike the fronts that were improved by bmw.

 

I’m guessing I’ll have to do something like this where I cut out the trunk to get to this pocket area and put my metal plate and bolt here.

 

see my sig below

 

Update: Been a little bit since this post but wanted to say that drilling the subframe bolt hole out worked flawlessly almost a little to good haha. Subframe definitely is nice and tight to the chassie unlike before we’re when it was put into gear the torque made the subframe hit the chassie being it was only supported by two front bolts and only one rear bolt. Thanks everyone for the help.

 

Perhaps a little welding to finish it off?

 

Good idea I’ll finish it off this weekend.