Posted 18 May 2012 - 06:50 PM
Well, no need to panic at this time. I would first get the bars off to make sure you dont have issues with the other 3 front mounts. If they are OK then as stated earlier, its only 1 of 8 and it may be savable.
Once the bars are off (hopefully the other 3 are ok) check to see how much farther the tread goes into the block past the broken section. Based on the Pic you may actually have enough to do the job. You really need a minimum of 1/2 of thread left over, if its more then that is even better. The trick may be getting the bar and broken bit out as chances are some of the threaed postion is in the broken section making it hard to remove from the bolt. You will probabaly need to put the broken bit in a vise and soak it with a form of penitrating oil and get the bolt out.
Now, if you have at least 1/2" of thread left in the block, you wont need to have the broken bit welded on, but it will have to go back as a "spacer" if you want to use new bars. So, lets say you have the 1/2" thread left in the block, here is the best and cheapest way to fix it. Take the broken bit and drill out the threads so the bolt will pass straight through it (you dont want any threads in this bit, just a clean hole the bolt can pass through without "pulling" on it. Now, clean the bit and block well, and glue it back on with JBWELD. You can hand tighten a bolt in to hold it in place while the JBWELD sets.
Now, if you dont have 1/2" minimum of threads, based on this pic you can tap the threads deeper provising the hole doesnt bottom out. If it does you can carefully drill the hole deeper BUT ONLY AS FAR AS WHERE THE SECTION MEETS THE BLOCK. If you look at the pic, it looks like you have approx 3/4" of mounting tab BEFORE it joins to the "meat" of the block. Drilling deeper could compromize a passage, so use a drill stop to prevent this. You can then tap out the hole and your good to go.
You may want to check the hole depth (use a piece of wire) even if you have 1/2" thread, as it will give you an idea of where the hole bottoms out in relationship to the block. Threading a bolt in until it stops will tell you how deep the threads go (most threaded holes will be deeper than the threads are). You may choose to tap a little deeper to get more threaded area.
I will not keep my fingers crossed for you that the other 3 come off without damage (use penitrating oil/rust buster stuff before just to help) and that you have a lot of thread still left. Remember you may need to get a bolt a fraction longer (most bolts only go in to the first half of a threaded hole to make sure the bolt never bottoms out.)