Baffling quill stem issues, new assembly

[Korvu]

I just purchased a new bike, a 2011 Marin Bridgeway.

Unboxing and assembly went pretty great until I threw a bit of weight into the handle bars and the stem twisted without the forks.

So, I reefed on the tightening bolt. Just enough to hurt the thumb pushing the allen wrench. I didn't want to bust any threads but it was good and hard. It still slipped under moderately hard handlebar pressure.

Disassembled, everything seemed ok, looked down the steer tube with a flashlight from the top, everything seemed all right. Put it back together. Same problem.

Now, I'm no bike tech but I have assembled half a dozen in my life (granted, it's been about 15 years). I do have a basic laymans understanding of how a quill stem is supposed to operate.

After reading the forums here and searching Youtube to the best of my ability, I took out the stem bolt and examined the stem and wedge carefully. I only have a low quality camera on my phone, so unfortunately I can't get pics good enough to show what I'm talking about.

The "long side" of the stem itself has slight indications of wear on about the first half inch of its length, just along the leading edge, on the outside/steer tube contact surface. When I looked very closely down the steer tube, I saw some brightness at that depth, like maybe a little scratching. I took a long thin bit of wood and ran the tip along the inside of the steer tube, and if there was any gouge it wasn't deep enough to catch the wood.

So...I tried tightening it bottomed out, I tried tightening it as just deeper than the max height line, it just didn't matter. It would seem snug, until I blocked the tire with my foot and gave a moderately forceful twist to the handlebars.

Also, when I look at the contacting faces of the stem and wedge, where they ride against each other, I see what looks like a bit of metal transfer (just a tiny bit) only along the shortest part of the wedge/longest part of the stem. It's like they're not making 100% smooth face to face contact.

Not that I'm sure if they should. I've never had to look this closely before.

Any help would be endlessly appreciated. I don't really have the cash to take it to the shop for assembly, or I would have. Heck, if I had the extra money I would have bought a nicer bike.

[Korvu]

Well...

Ok. This is just a little embarrassing. A lifetime of goonishly over torquing and stripping everything from motherboard screws to head bolts made me overly cautious. Also, in the past I always assembled bikes with my auto tools, which meant hex tips and socket wrench.

There's a big darn difference between a three inch allen wrench and an 8 inch socket wrench handle in terms of lever arm. Spec on this bastard is 175-200 inch pounds, or about 60 lbs pull from the very tip of the wrench. Instead of, well, about 25 lbs with the longer lever arm.

This will sound completely nuts, but I went out and lifted a 5 gallon bucket full of water by the wire handle with two fingers. Ok, 40 lbs. Set another gallon of water on the lid and did it again. 48 lbs. It's a lot more than I thought.

Also...steel forks. Really no reason to be overly paranoid about damaging the steer tube, at least not unless I used something more than a 3 inch allen wrench. With aluminium frame and stem and handlebars....I just forgot it's got a steel fork.

My Bad. Suffice to say, problem solved.

[DaveM]

Sounds like you just weren't torquing it enough. But for the record, when this happens, sometimes it helps to sand the angled surfaces where the wedge and end of stem slide against each other. These surfaces should be smooth and greased. I've seen small irregularities on these surfaces prevent the wedge from tightening adequately.

[nfmisso]

And use a torque wrench Even a $10 one from Harbor Freight is better than nothing; just remember that is probably is ± 20% of the indicated reading, unless you calibrate it.

[Korvu]

(08-07-2013, 01:22 PM)nfmisso Wrote:  And use a torque wrench Even a $10 one from Harbor Freight is better than nothing; just remember that is probably is ± 20% of the indicated reading, unless you calibrate it.

They've got a 1/4 drive 20-200 inch pound for 20 bucks. That covers the torque spec on everything on this bike (now that I've got the specs).

There's no carbon fiber. + or - 5 or 6% won't kill me on this bike if I aim for the middle of the range on everything.

Very good idea