Tapping Threads in Rear Subframe?

12 replies to this topic
  • danbart

Posted March 28, 2006 - 07:17 PM


I had a bolt break off and ruin the threads in the rear subframe where the rear fender / SCR subframe mount to the XRs rear subframe. Is it possible to tap a larger diameter tread into the frame or is this not going to work since it's aluminum?


  • Thumpmeister

Posted March 28, 2006 - 07:31 PM


You should probably just try to stick a longer bolt through and put a nut on the end. Since the aluminum is relatively soft, if you have a larger hole, it will probably weaken the mounting system, and might actually tear the alum if you get in a bad enough accident or something.

Think about the BRP footpeg; when it finally breaks off, you have to end up drilling the threads out anyways and stick a longer bolt all the way through. You don't make the hole larger and tap new threads because that would weaken the frame.

Just my .02

  • emyhrer

Posted March 28, 2006 - 08:16 PM


I had to tap new threads in my sub frame when mounting the left rear turn signal from my Baja Designs kit. Either the previous owner broke off a bolt in the existing hole, or there was never a hole there (didn't look like there was ever a hole, but I'm pretty sure the sub frames all have them). No problem drilling a whole and tapping threads of the original diameter and thread pitch. Of course, there's not much stress at that point on the sub frame, so even if it is weaker it shouldn't be a problem :thumbsup:

If you're worried about weakening the mounting point, you could consider using a helicoil or some other insert. That would let you use the original bolt also.

  • XR4DEZ

Posted March 28, 2006 - 08:33 PM


Can you use a heli coil?

  • gnarly sprockets

Posted March 29, 2006 - 04:54 AM


You could have the existing hole filled by a TIG welder then redrill and tap to the original size.

  • danbart

Posted March 29, 2006 - 08:36 AM


Thanks for the replies. just so we are clear this is where I'm talking about, so there is no way to drill through nad put a nut on the back side:


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  • emyhrer

Posted March 29, 2006 - 09:52 AM


The new threads I tapped on my sub frame was the right red arrow in your diagram (above the 23). Again, since I only mount my left rear turn signal there, there shouldn't be much stress in my case.

I don't have much welding experience, but I would think it would be easier to use a threaded insert instead of filling the hole and re-drill and tap. If you use a threaded insert, you should end up with stronger threads than the original aluminum also. I'm no engineer, so if someone sees a reason this wouldn't work, please feel to chime in.

  • cleonard

Posted March 29, 2006 - 10:03 AM


Use a threaded insert aka helicoil. Most autopart stores will have the kit that has the inserts, the special tap and the installation tool. It's like $25 or so.

  • danbart

Posted March 29, 2006 - 11:30 AM


Great info! Thanks guys.

  • motomonte

Posted March 29, 2006 - 04:26 PM


I can asure you that any of those metods won't hurt your bike.Just decide how much work/money you want to spend.Also wathever you do keep the threaded assembly tight since vibration is what can cause the more damage.Good luck.

  • Thumpmeister

Posted March 29, 2006 - 07:18 PM


I have the exact same prob on my bike, except I can't get the bolt out; the stock nut on the inside just keeps spinning. Horrible design on Honda's part, IMO...

I don't know how to get the damn thing out... I think I might end up cutting/drilling, but I don't want a nut/bolt ratting around inside my subframe...

  • skyriver

Posted March 29, 2006 - 11:03 PM


My left rear fender bolt that threads into the end of the sub frame stripped (steel insert broke away from the aluminum) as well. I had a Pro-Moto Billet Rack-It and took it off one time. That was all it took. The next time I put it back on I tightened very carefully, but still broke the dumb thing. So since then I've just tried to use a larger or more coarse bolt in the actual aluminum. The rack has been replaced by a fender bag so there seems to be less stress on that point now, but I know that bolt won't stay for long. Very dumb design.

  • HRCMan

Posted March 30, 2006 - 09:42 PM


Just a thought. The square tubing on the sub frame has a piece of solid aluminum square stock that fits the I.D. of the frame. It was probably drilled and tapped before being welded in place. I can't tell how far this piece is inserted if any, but I do know that I have 3/8" of thread on each side.

Mine definitely has enough meat to install a helicoil and not worry about it again.

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