Ideas on how to fix this?

Smaug

Well-known member
Local time
6:09 PM
Joined
Jun 9, 2022
Messages
1,263
Location
SE Wisconsin
I seem to have stripped the holes for the rear light and fender on my Lectric XP Lite. (I must say that it didn’t take much at all)

I guess the thing to do is drill them out a bit and tap them for a bigger (and coarser!) thread? Then go easy on the tightening and use thread locker instead?

Any other ideas or is this the best way to go?
 

Attachments

  • IMG_3939.jpeg
    IMG_3939.jpeg
    232 KB · Views: 112
  • IMG_3940.jpeg
    IMG_3940.jpeg
    195.1 KB · Views: 112
Solution
I agree with the rivet nut recommendation. However, if it were my bike I would try going oversize by drilling and tapping to 1 milimeter for an oversized bolt. Fine thread gives better holding power. Even if it drills out the insert, you would need to do that before compressing a rivnut into the crossmember anyway.
The simplest way if possible would be some new bolts of the correct thread long enough to come through the back and put a washer and nut on.
Only possible problem with this is that I would then have to drill through the back of that piece. It would weaken it as well as compromise the paint. (I'm not worried about the paint in that area, but about that being the source of it flaking away over time)

On the other hand, it is very simple and will surely work to affix the fender & rear light. I will take another look when I get some time without some girl or woman asking me to do something at home.
 
Consider rivet nuts. You must buy the tool, which usually has an assortment of the rivet nuts. Mine has been very useful many times.
I'm looking into this. I can see how it would be very useful in some situations. (even though I'm not a bike builder)
 
Consider rivet nuts. You must buy the tool, which usually has an assortment of the rivet nuts. Mine has been very useful many times.
Does this also require drilling the hole all the way through the tube, so I can put the rivet nut in the other side, or does the nut go in from the side where the screws did?
 
The rivet nuts go in from the side you drill. You don't need access from the other side. I've used them for several projects - mount a ham antenna to a truck bed, attach a clasp to a plastic storage cabinet, repair stripped threads. You do need ample space to drill that larger hole, but the nuts have a good thread length and are very strong.
 
I agree with the rivet nut recommendation. However, if it were my bike I would try going oversize by drilling and tapping to 1 milimeter for an oversized bolt. Fine thread gives better holding power. Even if it drills out the insert, you would need to do that before compressing a rivnut into the crossmember anyway.
 
Solution
Hsd makes good points. I'm switching my vote! And if tapping does fail for any reason, rivet nuts would still likely be a backup plan.
 
I haven't had time to get down and look at it again yet, but the more I think of it, the more I like the idea of through-drilling it and use a locknut.

While I'm at it, I need to grind the fender bracket down a bit. It overhangs too far back and blocks the hook for the rubber strap for the lock case that's behind the seat tube...
 
Bosses for accessories are standardized on bike frames at M5 x 0.80. For brake components (the mounts only, usually) its M6. You can test this by checking if your screws fit those two rack bosses just to the right/left side of your crossbar. They should fit perfectly, assuming no paint in the threads gumming them up.

Tapping to M6 would be the cleanest solution. You'll have to drill out that plate to fit an M6. If the frame is alloy I'm not sure I'd be crazy about thread integrity though. Sounds like thats already an issue.

Rivnuts will work. But its more tool-buying and work than just an M6 tap. You probably need to drill it out to that size at least to do a rivnut anyway so probably a simple M6 tap is not going to hurt. This is more likely to be a one-and-done than tapping to M6.

Drilling thru the frame and then using a longer M5 bolt, washer and nylock nut would do it. But I always try not drill holes in the frame unless it is an absolute last resort.

And then of course there's no drilling at all. JB Weld the little bugger in. Obviously sub-optimal in some respects.
 
Lots of great ideas. However, I would point out that just because bicycle brake hardware is usually M6 doesn't mean this repair has to be. Maybe a good ol' 1/4-20 would do here.

I have my dad's old tap & die set. I doubt if it has any metric sizes. Most of my spare hardware is also not metric.

I also might need to buy a set of quality drill bits, unless I can find one close that uses a standard fractional size.

Can someone recommend a drill bit for the M6? Maybe I can buy just the one drill bit with the right size tap....

I looked again today, and I don't think I want to through-drill that piece. It is at least 2" thick and is elliptical in shape.

The frame is aluminum alloy and the holes appear to be too. (it doesn't seem to have a rivnut in) Should I go back to the rivnut tool idea, for thread integrity? I don't think it will be necessary though. The threads will be tougher, as I'd be going up a size and I would take it easy on tightening and just use blue Loctite.
 
Can someone recommend a drill bit for the M6? Maybe I can buy just the one drill bit with the right size tap....
At Home Depot, the Milwaukee bits are in SAE units, but they show their metric diameter on the front label. One of them is IIRC like 6.2mm or thereabouts and that is essentially an M6 hole. Those are what I use. If you have the money, you can't beat a good step-drill bit. I have another Milwaukee kit that has two of them in it but thats about $60-70.

But if drilling all the way thru, there's no need to go up to M6. A thru bolt and nylock is going to be waaaay stronger. Its oval tubing but a washer on each side will keep the nut and socket cap from digging into the frame just fine.

Vibra tite is much better on something like a bicycle. Get it on Amazon. Comes in an easy-to-apply gel. The blue stuff. It never hardens. Originally developed for the aviation industry for resisting severe vibration. Its the locker of choice for competitive long range shooters and their delicate scope ring bolts and mounts, that suffer from major recoil shocks.

I have never done a rivnut. But I worry about tapping M6 and those threads in alloy that has already failed once.
 
1/4 inch drill will be fine.
you don't need as much torque as you think, but since you DO, definitely drill through and use steel bolts and nuts so you can hammer down.

basic chart:

 
At Home Depot, the Milwaukee bits are in SAE units, but they show their metric diameter on the front label. One of them is IIRC like 6.2mm or thereabouts and that is essentially an M6 hole.
I just looked it up and the correct drill bit size for an M6 tap is 5 mm. 6.2 mm would be way too big:

Those are what I use. If you have the money, you can't beat a good step-drill bit.
Step drills are for drilling holes in sheet metal; wouldn't work here, because I need the hole with some depth to it.

I have another Milwaukee kit that has two of them in it but thats about $60-70.
I work at Snap-on, so I don't buy Milwaukee. They are our main competitor and they are patent trolls.

But if drilling all the way thru, there's no need to go up to M6. A thru bolt and nylock is going to be waaaay stronger. Its oval tubing but a washer on each side will keep the nut and socket cap from digging into the frame just fine.
Through hole would be stronger if we're just talking about resistance to it pulling out, but on the other hand, it would weaken the part unnecessarily, in this case.

Vibra tite is much better on something like a bicycle. Get it on Amazon. Comes in an easy-to-apply gel. The blue stuff. It never hardens. Originally developed for the aviation industry for resisting severe vibration. Its the locker of choice for competitive long range shooters and their delicate scope ring bolts and mounts, that suffer from major recoil shocks.
This sounds perfect; like something that should be in my toolbox anyway. I'm going to get some; thanks for the recommendation.

I have never done a rivnut. But I worry about tapping M6 and those threads in alloy that has already failed once.
Drilling out and re-tapping seems like the least ghetto way to do this. It's not like it's a piece that was bent, then bent back; the material that failed is gone; ripped out by the old fastener. I'll remove a bit more material by drilling, then cut threads in the virgin material.

By the way, I think I just found the perfect wrench for getting to the axle nut on the wire side of the rear hub. The protective cage only allows about 1° of throw with my small crescent wrench. My metric combo wrench sets don't have 18 mm, for some reason.
1684354150268.png
 
Why not just scrap the bracket, and mount the taillight under the seat?
A few reasons:
  • The bracket fits and I'd need to find something else to mount it
  • The seat height gets adjusted a LOT between my daughter and me both riding it (she's 4'10" and I'm 5'8") The cable isn't long enough and if it were, it would mean a lot of flexing.
  • I need these holes anyway, as they're used for mounting the fender
 
1/4 inch drill will be fine.
you don't need as much torque as you think, but since you DO, definitely drill through and use steel bolts and nuts so you can hammer down.

basic chart:

Assuming you're referring to my using 1/4-20 bolts, it looks like a #7 (13/64" = 0.203") is the correct size. (LINK)

1/4" would be too big and I'd have the problem of threads stripping easily again.

I wonder if that's what happened at Lectric in the first place?
 
Back
Top