Bicycle Mechanics - Handlebar won't stay tight

I had to buy a new stem for my bike. I have an oversized, extra wide in the center, handlebar.
The top and bottom clamp sides of the stem (where the handlebar is attached) do not touch after tightening. I have tried "locktite", and adding "padding" --- but when I ride the hoods and extert extreme pressure (when breaking at the end of a steep downhill, the bars rotate downwards.

Its easy enough to tighten, but it is a pain.

Does anyone have any ideas?

Thanks,
glenna

Loctite will only keep a fastener in place. "Padding" is a vague term. You either need to get a stem from the same people who made your handlebar or find a proper shim to take up the open space between the stem clamp and the faceplate.

what is padding? anyway, grease the threads.

sd

It sounds like your handlebars are 31.8mm (oversized). Are you sure you got the appropriate stem? Also, most faceplates will exhibit a small bit of gap even when tight. If there's a very large gap (bigger than a 1/16") then you probably have the wrong size handlebar clamp on your stem. As others have said, grease the threads and if it's an open-face multi-bolt faceplate make sure you are tightening everything evenly. Also make sure the gap is equal at all the interfaces. A torque wrench is a good idea. Another idea would be to go to a stem with four bolts as opposed to just two if you haven't done so.

Loctite will only keep a fastener in place. "Padding" is a vague term. You either need to get a stem from the same people who made your handlebar or find a proper shim to take up the open space between the stem clamp and the faceplate.

I cannot get the stem and handlebar from the same place.
About the shim, are you saying there should be NO open space between the top and bottom of the clamp?
i.e. top and bottom of clamp do not touch, therefore the bolt threads are partly visible. Use the shim to cover the bolt threads?

My padding is a few layers of velcro (I am not using the sticky side).

what is padding? anyway, grease the threads.

sd

The padding is two layers of velcro cloth (sticky sides in).
What will greasing the threads do?

About the shim, are you saying there should be NO open space between the top and bottom of the clamp?
i.e. top and bottom of clamp do not touch, therefore the bolt threads are partly visible. Use the shim to cover the bolt threads?

My padding is a few layers of velcro (I am not using the sticky side).

My first suggestion would be to get rid of the velcro. I'm not sure that's doing you any good and most likely it's prevent you from obtaining a full clamping force on the handlebars. As I mentioned in my other post, you will most likely see tiny gaps between the faceplate and the stem when the clamp is fully tightened. Just make sure the gaps are all even. Did the stem come with instructions? Do the instructions list a torque spec? What material is your bar and stem (and stem faceplate) made of?

I will grease the threads, get rid of the velcro.
The gaps are about even and pretty small.

If that does not work I will look for a 4 bolt stem.

The handle bars are oversized. The stem was obtained by a local bike shop that really does know its stuff. I had to bring the bike in before they bought it for me...and they installed it.

The problem is, it is a hard fit. The stem rise is 45 degrees! I needed to get my seat level with my handlebar because of my back. Not many companies make a stem with this rise for oversized handlebars, however.

I will post back after the weekend with the results.

Thanks, all.

Also, I will look to see if there are torque specs.

If you want to use something to add a little more friction between the clamp and handlebars, try a small slip of sandpaper.

So what does your LBS say about the slippage? If they sold you the stem for an oversized bar, I'm sure they gave you the right stuff. Something's not right here. Oversized bar and clamp combo make for a very secure solid setup.

All you need to do is tighten it more.

No need for and of this crap these idiots are talking about.....grease......shims.....?????????

Tighten it...........

Use the torque specs and tighten it within them.

It's amazing to me that we spend amazing amounts of $ on bikes and associated parts only to disregard the instruction sheet and its wisdom. Torque specifications are from the manufatcurer who has spent a lot more $ than any of us making sure it will hold properly.

I have NO idea why anyone would shim and/or grease the threads on perfectly usable parts that were ordered specifically for this setup. Would you suggest I jam a stick in bewteen the brake pads and rim when the pads wear a little?

Sorry, but you need to trust the manufacturer with regard to torque...and USE a torque wrench. They go on sale at Sears every few months and are well worth the $60.

A torque wrench alleviates the gueswork of tightening a bolt. Sometimes it will "feel" too tight but not be even close to what it should be.

Tight is tight and too tight is broken.

PJ

I have NO idea why anyone would shim and/or grease the threads on perfectly usable parts that were ordered specifically for this setup.

Greasing threads is a good idea because it will allow the threads to distribute the torque load more evenly. The practice of greasing threads is common and is not a way to make up for any application difficiency. Shims can be par for the course too depending on intended application. My carbon bars came with a small sandpaper-looking insert meant to increase friction at the clamp area if need be. I didn't have to use it however as the clamping portion of the bar was already pre-roughened to the point wear slippage was not occurring.

I stand corrected.

Although (I'm guessing it's because I'm not an engineer) I don't totally understand why a little grease will distribute a load on a threaded part. The fact that the threads engage should already do that shouldn't it? I could see the grease allowing the threads to be seperated later on though.

PJ

You grease the threads so the bolt can be removed later. As you ride, you sweat, and that can corrode steel and aluminum parts.

Take the velcro padding out. If you need to shim the stem to the bar, cut an old coke can and use that.

I stand corrected.

Although (I'm guessing it's because I'm not an engineer) I don't totally understand why a little grease will distribute a load on a threaded part. The fact that the threads engage should already do that shouldn't it? I could see the grease allowing the threads to be seperated later on though.

Let's assume you're attempting to apply a specific torque to the bolt. What you're really aiming for is not necessarily torque but load. You want the bolt to be in tension to a specific load-value. If the threads are ungreased and binding then you'll see a higher coefficient of friction thus in a sense tricking you into assuming you've applied more load along the shaft of the bolt than you actually have.

You would need the shim if it were the other way 'round, that is, an oversize stem with a bar that's too small for it. If that were the case, the allen bolts would "bottom ou" but the stem would not be tight over the bar. As it stands, the stem isn't even all the way 'round the bar, so it can't be too loose/big for it. As has been stated, just tighten the allen bolts some more, until the bar stops rotating in the stem.

He may have a stem that was milled out just a bit too much where the bolts bottom out before it clamps the bar tight. OR, the bar was not formed correctly, and the stem doesn't clamp down enough.