Peter,
Good point about searching the archived, but, but....
I'm not trying to defend the so called cast aluminum "death stems". I'm merely providing some technical background that may help some make an educated decision about using a cast aluminum stem.
Many of the posts in the archives are about personal experiences, hearsay, urban myth and so on. Very few that I've read contain sufficient technical details to build a case for or against cast aluminum stems. Many comments claim that the stems broke at the clamps. That's not been my experience at all.
Back in the 70s I had 3 cast aluminum stems fail on me while riding. I worked at/managed a bike shop for 5 years. Two of the stems broke while test riding customers bikes. They were the cheap Bike Boom cast aluminum stems. The third was a Belleri cast aluminum stem on my own bike. It was the first generation Belleri model with a recessed hex head expander bolt.
Fortunately I was going slow enough to bring the bikes to a safe stop all 3 times. It's a very scary feeling riding down the street holding the bars in your hands.
All 3 of these stems failed in the same place, at the top of the expander split on the quill. The true "death stem" in the photo in the link below shows cracks forming at the top of the split. Also note the poor quality of the casting on this stem. Aside from the insertion depth ring, all of the other flaws were part of the casting. Note how the quill is bulged at the bottom. This is supposed to be a 22mm French stem but in places the quill is under 21mm in diameter.
http://www.postimage.org/
The late great Sheldon Brown (RIP) did both a service and a disservice to cyclists in his warnings about AVA "death stems".
The disservice is that it can give users of other makes of cast stems a false sense of security because they have a different make stem. People with a cast aluminum stem should be aware of the possible safety hazards with any these style parts not just AVA stems.
During the Bike Boom of 71 to 74 bike makers used what ever components they could get. We sold Gitanes plus a myriad of other French Bike Boom bikes. Gitanes usually had Pivo Stems. Peugeots (the competition) on the other used mostly AVA stems. I've seen far more poor quality Pivo stems than any other make.
Cast Aluminum stems have been used for over 50 years. They should not all be tarred with the "death stem" reputation.
Here's a partial list of French cast aluminum stem brands from the Bike Boom era. It's not complete and some stem makers used more than one brand name. Also there were private label stems like Milremo.
ATAX AVA BELLERI BF CTA GUID LEPPER? MILREMO PHILLIPE PIVO SINTESI
Stems that are not inserted far enough into the steering tube are one cause for the cracks forming at the top of the expander splits. The rule of thumb is a stem should be inserted at least 2" into the steerer.
But, but, but, you never know if the stem had been ridden for years with only an inch of insertion and is already damaged without doing a close inspection. Here's an example of what I mean:
http://www.postimage.org/
The other problem related to this is the possibility of expanding the quill in the threaded area of the fork. This can cause the threads to bulge and eventually crack. I repack the headsets on almost every bike that I work on, inspecting both the forks and the stems.
Many newer stems have an angled wedge that pretty much eliminates the cracking problem but they can still damage the fork.
Casting quality and the type of aluminum ally used are other important issues. Cast aluminum is used in most metal based products from automotive to aerospace. There are over 40 different aluminum alloys used for casting.
Porosity and microporosity is a major problem with cast aluminum. Some porosity is caused by precipitation of hydrogen gas during solidification from the molten state. Other porosity problems can be the result of impurities in the metal. In any case, porosity can result in cracks an metal failure. Many of the early cast aluminum stems used really cheap casting methods. Modern cast aluminum parts are made pressurized casting equipment which reduces the amount of porosity in the parts.
Forged aluminum stems tend to be much stronger that most cast stems because the metal is much denser. Forge melting is a marketing term for pressure cast parts.
Advice for using cast aluminum stems:
1. Inspect the stem carefully. Look for any signs of cracks or porosity. DON'T use any stem that doesn't look good!
2. Drill a small hole in the quill at the top of the expansion split or splits. This will reduce the tendency to crack in that area.
3. Don't use a bar that's too small or too big to fit the original size that the stem was designed to use. French stems usually used 25mm bars and 22.2mm quill size stems used 25.4mm (1") bars. Aluminum in general can be fairly inflexible, especially so with casting.
4. Almost ALL of the French aluminum bars from the Bike Boom era should be suspect. Any sign of sagging or drooping, get rid of them. I have seen a number of catastrophic failures with these bars. For example:
http://www.postimage.org/
Chas. Colerich Oakland, CA
-----Original Message----- From: Peter Brueggeman <4peebee@peterbrueggeman.com> To: classicrendezvous@bikelist.org Sent: Thu, 2 Apr 2009 7:44 am Subject: Re: [CR] death stem? px-10
Regarding Robert Sasher's query about death stems by AVA etc, the Classic Rendevous Archives has considerable past discussion on this topic. I usually check the Archives first to read what has been discussed over the years. I frequently find what I need to know there, and don't post a query to the CR list. My observation has been that typical recurring questions posted to CR usually will not receive as good a range in responses as the responses aggregated in the CR Archives.
Go to http://search.bikelist.org/
Type in the Search String box
death stem
Select "Sort By: Date (newest first)"
Select "List To Search: classicrendevous..."
Click on the Search button
...........
Peter Brueggeman
La Jolla CA USA
4peebee(at)peterbrueggeman.com
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