Stem screws came loose when riding

So this morning I was going downhill on my road bike and I hit a (small) pothole. I heard a loud crack and looked down to find that my handlebars were loose against the stem. After I finally managed to stop and not crash into anything I noticed that one of the bolts which held the stem face plate on had come loose, and it turns part of the threading inside the stem itself had ripped off and came out with the bolt so it wouldn't fully tighten. Managed to swap some washers around so there was enough thread to reasonably tighten the handlebars down and get home.

I've got a spare stem which I'm going to replace it with but it was a rather scary experience which I don't care to repeat - has this happened to anyone else? Is it a problem associated with 2 bolt stems?

What is the stem in question?

Sounds like that stem bolt was overtightened. Given the surface area between the stem and steerer, they don't need to be tight at all.

Sounds like that stem bolt was overtightened. Given the surface area between the stem and steerer, they don't need to be tight at all.

Sounds like it happened at the other side of the stem. But I agree with what you're saying.

The stem isn't anything special. I think it's an older aluminium ITM "Millenium".

The stem isn't anything special. I think it's an older aluminium ITM "Millenium".

You need to

• clean and wax the handlebar/stem interface
  
• use assembly paste (a special kind of grease) on the bolt's threads.
  
• tighten the bolts to the recommended torque
  
  

Use of a thread lubricant (assembly paste) and proper torque is important. If you don't know what ITM advices one can generally use the values as specified for the bolt size. See: Bicycle Fastener Torque Specification

Wax stem/bars interface? What does this do - Stop creaks?

removes unsightly hairs

thanks, I'm here all week.

Why would you wax the handlebar/stem interface? Given that you depend on it not to move, lubricating it sounds like a bad idea to me.

Lubricating the bolts (with grease or something like the Finish Line anti seize) is a good idea, but what's 'assembly paste' in this context? I've only seen that name used for a carbon- specific product.

As for torque, normal sized allen keys are about the right length to apply the right sort of torque to the bolts they fit - snug them up good and tight, without swinging on the key like a gibbon. In the absence of a torque wrench, that'll be good enough.

Why would you wax the handlebar/stem interface? Given that you depend on it not to move, lubricating it sounds like a bad idea to me.

One needs to worry about fretting corrosion. That is also why one waxes or even lubricate (with an assembly paste) press fits such as those in square taper cranks.

Lubricating the bolts (with grease or something like the Finish Line anti seize) is a good idea, but what's 'assembly paste' in this context? I've only seen that name used for a carbon- specific product.

Those products are for assembly of carbon/carbon and quite different beasts from assembly pastes as used in metal applications-- e.g. automotoive.
http://www.klueber.com/en/lubricants/lubricating-pastes/

There are different kinds of lubricants for different kinds of applications. A good lubricant for high speed roller bearings, for example, has other demands than one to protect metal surfaces from tribocorrosion. Polymers such as Krylox might be great in wheel bearings to reduce friction, for example, but not quite the stuff to lube ones seatpost.

See also:
CORROSION CONTROL AND TREATMENT MANUAL tm584c

hippy always uses and recommends 4-bolt stems for this reason.
Talking about yourself in the third person is optional.

Then again hippy weighs twice as much as your average fixie skidder ;)

Why would you wax the handlebar/stem interface? Given that you depend on it not to move, lubricating it sounds like a bad idea to me.

Lubricating the bolts (with grease or something like the Finish Line anti seize) is a good idea, but what's 'assembly paste' in this context? I've only seen that name used for a carbon- specific product.

As for torque, normal sized allen keys are about the right length to apply the right sort of torque to the bolts they fit - snug them up good and tight, without swinging on the key like a gibbon. In the absence of a torque wrench, that'll be good enough.

Copper grease.

I use a 4nm torque key for face plates, stem bolts and seat post collar bolts.

^ This, fixed 4/5Nm torque keys are fairly cheap and will do pretty much all of the bolts that you'll find on a bike up properly.

I had bars come lose during a sprint tt coming around the 1st bend,
a 2 bolt stem with the correct torque used for the bolts, and assembly paste.

I stick to 4 bolt now, or 1 bolt quill stems. its a good idea to use some loctite on the bolts too, alot of stems come with some already applied tho

people often say i've got a screw loose .. i've checked and they're definately wrong