First let me tell you what I'm doing. I plan to mount a small bracket to attach my Ohlins shock oil reservoir clamp to the inside of the frame just under the tail. I plan to use the bolt hole for the exhaust hanger to anchor the small bracket. To do this, I will need to use a longer bolt in the exhaust hanger so that the threads protrude about a half inch on the inside of the frame. Then I plan to fasten the bracket to the protruding threads with a nut.

The problem is that the longer bolt I bought for the rear exhaust hanger bolt hole will only thread in 1/2" and then it stops. The OEM bolt feels a little sticky in a couple spots as I thread it in but it goes all the way through to the inside of the frame which is about a full inch. WTF? Are these self locking threads in the frame? I tried both the OEM bolt and the new bolt in the front exhaust hanger bolt hole and they both threaded through just fine. ...so I think there is something weird about the threads in the rear hole (rear exhaust hanger bolt hole, that is--LOL). I did not want to turn it any tighter than I could with my fingers. If it doesn't go in smoothly, something is probably wrong.

What do I do?
Try a wrench on the new bolt to see if I can force it through?
Try a thread chaser?
Try a brand new high quality bolt? The bolt I bought was a lower grade because I am just using it for test fitting. I plan to get a nice aluminum bolt for the final install.

There are a few good comments about thread cleaning on this thread.

http://zx14ninjaforum.com/messages.cfm?threadid=A1F29B5A-1372-66AE-3B1634E489C693DA&page=1&searchTerm=damaged%20threads#12

I guess I have encountered this problem before but this is the frame. I don't want to screw that up since the OEM bolt seems to work fine. If only it were longer, I wouldn't need to bother with this.

* Last updated by: Rook on 2/7/2015 @ 6:19 PM *

I'd try to run a tap through there. You know the deal, in a bit out a bit until you get the threads cleaned out.

Running a tap thru with a little oil would be my first step. Double check to be SURE you have a metric bolt with the correct thread pitch would be second.

Some bolts have a thread pitch so close you can't tell the difference by eyeballin' it. If you have a die the correct size then run it down the bolt, easy way to tell and also make sure bolt threads are clean and straight.

wow, thanks for the fast responses!

I'd try to run a tap through there. You know the deal, in a bit out a bit until you get the threads cleaned out.

Double check to be SURE you have a metric bolt with the correct thread pitch would be second.

If you have a die the correct size then run it down the bolt

If all else fails, I'll tap the bolt hole in the frame just a little at a time. From all of the indications, it seems like that is the real problem.

* Last updated by: Rook on 2/7/2015 @ 7:21 PM *

Did you look in there with a light?They should be the same.You say the front one went fine.How about on the other side...same thing?

I looked in there with a flashlight but it was hard to tell if I was seeing damaged threads or just ordinary reflections. I'll have to peek at it again tomorrow.

I did not try the other side to compare. Good suggestion. I'll try that tomorrow, too.

Good news is that I already have an M8 tap. I'd rather try what is known as a "chaser" or thread restorer. Hope I can find one locally.

The majority of these guys seem to think a chaser is no better than a tap.

http://www.practicalmachinist.com/vb/general/thread-chaser-tap-237679/

I wouldn't go and tap out the entire depth of already cut threads if that is not necessary. From the little I have seen, a tap will remove metal from brand new threads and the bolt will fit looser after running a tap through.

You can see from this picture that the bolt I bought is getting cleaned off as it goes in deeper. The point where the dirt stops is about as far as it will go in. Seems to me like the threads in the bolt hole may be tapered as they go in deeper. IDK if it's supposed to be that way or if they just didn't run the tap through far enough at the factory.

I bough a higher quality (and clean) bolt today. It goes all the way through but then it stops after exiting the other side about a sixteenth of an inch. That is not far enough to attach my bracket.

I also picked up an M8 x 1.25 die. I plan to run the bolt halfway through the die rather than tap the hole. This should cut the threads a little smaller on the end of the bolt so that it can pass through the tightest spot in the threads at the bottom of the hole. Only problem is that the bolt will have threads that are a little looser where I fasten the bracket inside of the frame. Oh well, with a little LokTite it will work just fine. I'm going to have the oil reservoir safety wired anyway and there is another bolt hole under there that my bracket will be fastened by.

I know everyone is hanging on the edge of their seat to see how this turns out so stay tuned.

Thanks for all of the great ideas.

I think a wire brush with very short bristles would clean the dirt out of there and it might go in. If so, you can imagine how tight those threads must be. There isn't that much dirt on the bolt.

* Last updated by: Rook on 2/8/2015 @ 2:57 PM *

Grn, I cleaned the dirt out of the bolt with my fingernail and it didn't help at all. I tried the bolt in both holes on the other side and it went to the bottom of the hole and stopped after it just peeked out of the other side.

I think these threads are designed to be tapered so they self lock. When the taper in the first few threads on the bolt widen to their max diameter, the bottom threads in the hole are too tight for them to pass through. I'm not tapping these holes unless they really are damaged some day. I'll die the bolts to make them stick through if need be.

Hey guys (and anyone who searches this out in the future), if your still following the Thread thread, I had easy success. If you recall, I bought a high quality bolt. It still would not go through the threads in the frame all the way through the bottom of the hole but it did thread in right up to the last thread. I need it to stick out under there a half inch.

I didn't even use a die on the bolt and I didn't have to tap the original threads in the frame, either. All I did was run the last 1/2" of the bolt threads over some 220 emery paper. I went around the circumference many times to keep the removal of metal even all around. I ran it across the emery paper with medium firm pressure about 200 strokes. The nut now feels just a tad bit more floppy on the sanded down portion of the bolt. The bolt went through the bolt hole in the frame + the extra 1/2" I sanded now protrudes underneath like I want it to.

Original threads in your bike are tapered. Probably all of them are. This helps them hold onto the bolt as it threads in deeper. The reason bolt holes have tapered threads is that taps are tapered. If you run a tap all the way through a bolt hole in the frame, you widened the bottom of the threads where they once had a tighter grip on the bolt.

So, if a new high grade bolt won't go into old threads, DON'T tap the threads. Just measure how much it is sticking out and then sand that same amount off the tip of the bolt. If the threads in the bike are in like new condition, why touch them with a tap?

Case closed.

* Last updated by: Rook on 2/10/2015 @ 11:52 AM *

If the threads in the bike are in like new condition, why touch them with a tap?

I plan to fasten the bracket to the protruding threads with a nut.

The nut now feels just a tad bit more floppy

Hmmm...now you have to shrink your nut. Always something aye?

LOL I'm not worried about the nut. It's just a tiny bit looser. Not even noticeable unless you knew the the threads were reduced. The nut will tighten up just fine. I'm sure I took off only about .005". Maybe I will mic it before I install it permanently.

I guess the word "floppy" had me worried a bit.lol. Glad you got it figured out, I never had any doubts.

Rook, glad you worked it out! Sometimes the simplest things, sandpaper, work the best!

Thanks. Yeah, seems to have done the trick.

One more update, I ended up buying a second new bolt. It goes through without sanding the threads down. I think all I had was a bit of paint or some dirt in there. Oh well, pays to be careful.