Screws don't fit. Am I screwed?
September 11, 2010 4:41 PM   Subscribe

Installing rear rack on bike. Bolt size conundrum.

I'm installing this Topeak Explorer rack on this Fuji Absolute 4.0 bike.

This should be really easy... except the bolts don't fit the lower threaded inserts (the ones in the rear dropout area) of the bike. They do, oddly enough, fit the threaded inserts in the seat stay area. When I try to screw them into the lower threaded inserts, the bolts seem just slightly too big. It almost seems as if the paint is what is keeping the bolt from screwing in. The holes on the seat stay are counterbored, while the lower holes are not, so this may make a difference.

I'm looking for 1) possible explanations as to why the bolts on this "one size fits all" bike rack seem to fit one set, but not the other set of threaded inserts on my bike, and 2) suggestions as to how to get these to work. It seems like if I was to put the bike on its side and then push really hard on the bolt, I could get it to screw in, but this is not an option for obvious reasons. If they just won't work, I'll have to pay a bike shop to do it for me, and figure out what size bolts work (I'm too impatient to play trial and error), but I'm hoping to be able to finish this job myself.
posted by elpea to Sports, Hobbies, & Recreation (8 answers total)
It could be the paint. get a proper size tap & use that to clean out the treads. IANABM
posted by patnok at 4:52 PM on September 11, 2010 [1 favorite]

Are you sure the holes at the top and bottom are threaded the same? Is it possible that one is machine thread and the other is fine thread? If this is the case, even if the bolt sizes are the same, the same bolt won't fit in both holes. Look carefully and see if the threads look exactly the same. If I was unsure, I would not force the bolts. I would take the bike to my neighborhood big box "hardware store" and ask the guy in the orange or blue apron if there is a bolt that fits the lower holes. If the threads are the same in both sets of holes, he can sell you a tap to clean out the holes and, either way, you'll be on your way.
posted by Old Geezer at 5:09 PM on September 11, 2010

Best answer: It almost seems as if the paint is what is keeping the bolt from screwing in.

Yes. This happens all the time. The threads are the same, but some paint gets stuck in there when the frame is painted and then the bolt won't fit. If you can't get a bolt in from the outside, try it from the inside. Otherwise, a tap is the solution. A bike shop can probably do this for you, if you don't have access to metric taps.
posted by ssg at 5:27 PM on September 11, 2010

I doubt it's paint.

From the picture it looks as if the threaded hole on the seat stay actually goes into a large hole in the seat stay itself rather than a braze-on. I had a much older Fuji with the same arrangement, and I haven't seen threaded holes for screws as large as it takes in a dropout.
posted by jamjam at 6:09 PM on September 11, 2010

Best answer: I have that rack on my bike, and had the too big bolt problem. I just bought a bolt slightly smaller and put it right through the hole - used a regular nut and a lock nut. If you don't have to match the thread in the frame, you can go to the metric or standard size just below the size of the hole. It's been on with the Topeak basket since January, and hasn't loosened at all, even with a hazardous amount of groceries inside.
posted by figment of my conation at 10:00 PM on September 11, 2010

Best answer: The bolts should be metric, and will be either M5 or M6. If those bolts aren't fitting, then the most likely problem is, as has been suggested, some sort of gunk clogging up the threads, or alternatively the threads mightn't have been properly tapped to begin with. 5 minutes with an M5 tap should be all it needs.

It's not a bad idea, when installing racks, to thread the bolt such that the head is on the inside of the bike and the threaded portion on the outside. Then use a locknut to secure the rack to the exposed threads. The beauty of doing it this way is that is the bolt ever shears off, you can just back out the bolt and replace it. If you've threaded it the conventional way then you're stuck with a broken off threaded bolt in the hole.
posted by tim_in_oz at 11:05 PM on September 11, 2010

You can usually tell when it's paint because you can tighten it a half turn or so, then loosen it a half turn, and then when you tighten it again it should feel like there's almost no resistance until you get to the point where you stopped tightening previously. However, if you're tightening through thread that you've already been through and it doesn't feel smooth and easy then it's probably not paint and the bolt is cross-threaded and you'll only ruin it if you try to go on.
posted by Rhomboid at 5:32 AM on September 12, 2010

If you have a community bike shop around, call them and see if they have taps and can help you do that. A tap and die set isn't really that common of a tool to have unless your a machinst or a bike geek, especially the metric/bike specific taps. They're also easy to break if you're not careful. I can't imagine a bike shop charging much to tap the holes, if you bought the rack at that store I'd hope they'd do it for no-charge. Don't pay more than 10$ for it, it's a 5 minute job.
posted by glip at 8:44 AM on September 12, 2010

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