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How do I remove rust from threaded hitch holes in a box frame?

I have a 2002 Jeep Liberty and the correct hitch and mounting hardware (bolts and washers).  Unfortunately, the holes in the frame are very rusted from the 8 years of driving without a hitch.  I can't even get the bolts to seat properly.  I checked and made sure that they are the right bolts for the vehicle.  I tried a thread cleaner kit from a local garage but wasn't able to make any progress.  Soaked the holes with WD-40 but still no luck.  I can't put a nut and washer on the other side because it's a box frame.  I'm debating using a brass bristle brush on a drill to try to clean it out but that could ruin the threads.  Any ideas?

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Try Liquid Wrench.  WD-40 wouldn't be able to do it.

There are other chemical rust removers that you can buy at Home Depot and such, but I can't vouch for using them on a vehicle.

Failing that, I like what NachoMahma and Burf suggested.
 
connoljj (author) 7 years ago
Thanks everyone for all of the great information and ideas.  I did exactly what you all recommended starting with the easiest and thankfully the higher strength liquids actually got the thread cleaner to work.  And it was very hard work but it paid off.  I was able to get two of the bolts in all the way and good to go.  One hole got completely stripped unfortunately and the other I was only able to go about half way because I think I was cross threaded.  I'm going to keep working on it.  Thanks again for all the help.
connoljj (author) 7 years ago
Thanks everyone for all of the great information and ideas.  I did exactly what you all recommended starting with the easiest and thankfully the higher strength liquids actually got the thread cleaner to work.  And it was very hard work but it paid off.  I was able to get two of the bolts in all the way and good to go.  One hole got completely stripped unfortunately and the other I was only able to go about half way because I think I was cross threaded.  I'm going to keep working on it.  Thanks again for all the help.
NachoMahma7 years ago
.  Drill out the existing holes and re-tap for the next size larger bolt. You may have to drill slightly larger holes in the hitch.
.  If you need to remove the hitch for an extended period, slop some Never-Seez (or equiv) on the bolts and put them back in the holes. This will help prevent dirt buildup and corrosion.
Nacho=best answer.
Depends, there may not be enough metal on the insert they use to do that.
.  Surely a hitch mount point would be more substantial than an insert. Wouldn't it? If it is a light-weight insert, then forget my idea - not worth the risk of weakening it and having the hitch fall off when pulling a load.
seandogue7 years ago
I would start by using a tap of the same size as the existing bolts, in order to see if you can preserve them as is. The rust is definitely deterioration, but rust is expansive and doesn't necessarily accurately reflect the amount of damage to the unrusted metal.

if there is ANY play when they are inserted following retapping, do as MachoMahma said and go one step larger.


What about getting a thread tap the right size and running that it.

Steve
Don't forget to use a little oil on that tap.
Oh yes, or tapping lube.
Burf7 years ago
Most likely there aren't enough threads left for the bolt to thread onto.  Eight years of rust will have seriously eroded away the threads. 
You may have to have the bolt holes welded shut then drilled and re-threaded.
PS A brass brush would be OK.