So I pulled out the mounting bolt for the hose assembly and the threads for the compressor came along with it.... so I will definitely have to tap some new threads, but do I have to bother with drilling since the threads came out so cleanly?

 

New threads cannot be formed where sufficient ID of the bore does not exist, there is no metal to cut through with the tap to form the threads. Sometimes you "chase" a thread with the same size tap to clean up slightly buggered threads that are almost OK and are all there or to clean out the first couple of cross threaded turns so that the bolt can get to the meat of the threads but sufficient threads of high quality must still exist below the cross thread. Over tightening and pulling threads all the way down the bore is an entirely different animal. Once the threads are sufficiently messed up then you have two choices. Drill and tap using the next bolt size up if the the situation can tolerate the larger bolt or you have to drill and tap much larger and then place an insert in the new larger tapped hole which has larger OD threads matching the tap and the original thread size and pitch as its ID. That can be a threaded insert or a Helicoil.

You've got quite a project going here. Now your going to machinist and HVAC school.


George

 

I would go with a heli-coil, since it requires the least enlargement of the original hole. The actual drilling part of the heli-coil installation will take about a minute, so I wouldn't put too much effort into avoiding it. Even if the stripped out hole is the right diameter for the tap, the stripped part probably isn't deep enough.

 

Ya I was referring to the last course of action you mentioned where I place an insert in the tapped hole and then screw the original in the insert. I would prefer to avoid drilling if it's not necessary because I don't want to deal with a hole full of aluminum bits and it's just another thing for me to mess up. I was thinking that since the bore seems to be so clean now, I could just tap some threads, but now I am thinking that will mainly not work because I probably won't find an insert that is thin enough to fit in the tapped hole AND fit my bolt.

So it seems that I should try drilling and tapping for a slightly larger bolt, and if that doesn't work out, then I should go the insert/helicoil route because I can only make a hole bigger and not the other way.

 

If there are still good threads at the bottom of the hole, maybe you can screw a stud in there? If you just lightly tighten it and secure it with loctite, it should work.

 

Tom, if I understand correctly, the stud would secure at the bottom of the bore (because it's longer and maybe there are a couple of threads at the bottom), and I would secure it at the top with a nut? Loctite only at the top or bottom too?

 

That's correct. Loctite only on the threads holding it into the compressor.

 

And when you say the stripped part isn't deep enough, you mean that I would basically be in the same situation where I would still have to drill anyways, right?

With that and the thought of using a stud in mind, if I do have enough threads below, couldn't a longer bolt accomplish the same thing as a stud?

 

Yes. I mean that the Heli-Coil would not thread in far enough to work properly.

You could use a longer bolt, but the stud lets you use every thread, all the way to the bottom of the hole, without having to exactly figure out the bolt length within .001"

 

I guess my main concerns with using the remaining threads is: a) how do I know how many I have left; and, b) how do I know if they're enough to do the job?