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death stem? 
PostPosted: Mon May 05, 2008 5:09 am Reply with quote
tua
Joined: 17 Mar 2008
Posts: 7
Location: Golden/Crawford, CO USA
Like many TdFs, mine came with a Pivo stem that I've now riden on for three decades without any thought. Recently, I was perusing Sheldon Brown's site and he talks of the AVA stems on many French bikes, calling it the "death stem" for fracture problems. It looked remarkably like my "arrowhead" Pivo.

Looking elsewhere on the web, others stated that AVA and Pivo are really the same stems. However, others said that only the AVAs are bad and that the Pivos are the accepted replacement.

Anybody know definitively? Anybody ever break a Pivo (and live to tell the tale)?

Tua
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Tige de la mort 
PostPosted: Wed May 07, 2008 12:07 am Reply with quote
verktyg
Joined: 14 Jan 2007
Posts: 2628
Location: SF Bay Area
Funny you should ask. Surprised

I've been collecting some old French "Tige de la mort" death stems lately. I haven't gotten around to photographing all of them yet.

AVA and Pivo were separate companies. Here's a list of some brand names of French stems that I've been compiling. These were brands that were sold from the 1960s through the mid 70s and later.

ATAX
AVA
BELLERI
BF
CTA
GUID
MILREMO
PHILLIPE
PIVO

Not all of these were problematic and some manufacturers sold stems under several brand names.

Most of these stems produced from the 1960s until the mid 1970s were made of cast aluminum versus forged aluminum. Some were very well made but others were dangerous junk. The quality differed within the same brand and model.

Some of the worst stems were produced during the US Bike Boom between 1970 and 1973. The quality problem wasn't limited to French stems either. I've seen poorly made British and Italian cast aluminum stems from that era too.

Here's a picture of a Pivo stem with a crack at the top of the expander split in the quill. This was the most common failure point. The crack would continue around the quill until the stem broke off.



Also note the the area at the bottom of the quill is bulged. The quill was undersized and never machined. It was up to 1mm too small in various parts of the quill.



I have several French cast aluminum stems from the mid 60s that are beautifully made while some from the Bike Boom era have porosity in the castings.

Unlike steel, aluminum doesn't bend well. The crystal structure in poorly cast aluminum parts is susceptible to cracking especially when being stretched as in expanding the quill on a stem to tighten it in the steering tube or to clamp around the handle bars. Forged aluminum is much tougher and can withstand more flexing.

Back in the early 70s I had 3 cast aluminum stems fail while riding. Two of them were on customer's bike that I was test riding and one was a Belleri stem on my own bike. Fortunately I was going slow enough to keep control of the bikes and safely stop. I was lucky enough to push the stems further down the steering tubes and keep control.

A more scary experience was when a steering tube broke off at the bottom of the threads on one of my bikes. I was going down the street holding the bars in my hand with the top of the headset attached to the quill. Again I was lucking and was able to safely stop.

I recommend that any one using one of these old cast aluminum stems periodically remove them and inspect them for cracks. Also make sure that they are sufficiently inserted in the steering tube so the quill is not expanding in the threaded area of the fork steerer. Shocked

They are probably OK for casual riding but I would invest in a more modern stem and bars for any serious use.

Chas.
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PostPosted: Thu Mar 21, 2013 10:50 pm Reply with quote
Jakedpdw
Joined: 21 Mar 2013
Posts: 4
Location: St. Petersburg, Florida
Alright I know this was posted a few years ago... but I just bought an old ass Gitane. I'm trying to break it down to the frame so I can paint it but the stem and the forks are stuck together.

The research I've come up with so far has told me that there is suppose to be a screw of some sort, at the top of the stem, going down into the frame, thus "clamping" the stem and fork into the frame. The only problem...I don't have that screw there.

I've tried beating the shit out of it, greasing the shit out of it, beating it again and even brought it to a small local bike shop, in which he couldn't get it off either.

If anyone has any helpful suggestions, I'm all ears. Well in this case eyes.
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PostPosted: Fri Mar 22, 2013 5:20 pm Reply with quote
gman309905
Joined: 23 Dec 2012
Posts: 54
Location: Pittsburgh PA.
If you could post a few pictures, top, front and side views I might be able to offer a suggestion but I need to see exactly what your dealing with
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PostPosted: Fri Mar 22, 2013 8:07 pm Reply with quote
gmany
Joined: 20 Aug 2009
Posts: 46
I've had good success by uncrewing the bolt about 1/4" (make sure you are still engaging several turns of threads) and then I put a block of wood on the bolt and hit it with a hammer. The bolt pushed the wedge our of the stem.

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Garrett Miles
Saint Louis, Missouri
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PostPosted: Sat Mar 23, 2013 6:13 am Reply with quote
vanhelmont
Joined: 11 Dec 2007
Posts: 242
Location: Florida
Greetings from across the bay!

As gman said, pictures would help, but if the bolt is somehow gone and it's still stuck, the stem may be sort of chemically stuck to the steering tube. Dripping a little household ammonia around the stem where it goes into the steering tube will in seconds dissolve the aluminum hydroxide (or whatever exactly it is holding them together) so that they won't be chemically stuck any more. (This trick is from the late Sheldon Brown, whose web site, maintained by Harris Cyclery where he worked, has all kinds of info on fixing old bikes, especially old French bikes. Worth looking up if you are working with an old Gitane!)

Of course this assumes that the expander or wedge that is supposed to hold them together is somehow gone. If there is a hole at the top of the stem where the bolt used to be the wedge might still be down there. Then you might need to find an old bolt, maybe from the bike shop you patronize enough so they know you and will let you rummage through the junk box for old stuff, and put it in far enough to engage the thread, and tap the top to loosen the wedge.
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PostPosted: Sat Mar 23, 2013 8:20 am Reply with quote
Jakedpdw
Joined: 21 Mar 2013
Posts: 4
Location: St. Petersburg, Florida
Thanks for the replies and sorry for my lack of terminology :/
But here are a couple pictures that I hope can help.
The third picture is looking up between the forks from the bottom.






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PostPosted: Sat Mar 23, 2013 11:16 am Reply with quote
verktyg
Joined: 14 Jan 2007
Posts: 2628
Location: SF Bay Area
Jakedpdw wrote:
Thanks for the replies and sorry for my lack of terminology :/
But here are a couple pictures that I hope can help.
The third picture is looking up between the forks from the bottom.



The expander is still in the bottom of the stem.

As vanhelmont said, get an old expander bolt and put it down through the hole in the top of the stem.

If you can find one from an old French bike, you may be able to screw it into the wedge. If not, you can use it as a punch to knock the expander loose.




The picture below shows the older expander style stem like yours along with the wedge style that most stem designs switched to.

In this situation, the stems have been inserted too far into the steering tube and are expanded into the "butted" or thicker tubing section at the bottom of the tube.


_________________
Chas.
SF Bay Area, CA USA
==============
1984 Criterium
1969 TdF
1971 TdF
1974 TdF
1984 TdF x 2 Bikes
1970 SC
1971 SC
1972 SC
1984 SC
1984 Team Pro
1985 Professional
1990s Team Replica
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PostPosted: Sat Mar 23, 2013 12:43 pm Reply with quote
gman309905
Joined: 23 Dec 2012
Posts: 54
Location: Pittsburgh PA.
using the ammonia sounds like it might do the trick and any piece of steel or brass that is of the right diameter to fit through the bolt hole in the top of the stem and long enough to make contact with the expander could be used to drive it out of the bottom of the stem, I'm assuming you don't plan on re-installing this particular stem.
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PostPosted: Sat Mar 23, 2013 8:44 pm Reply with quote
Jakedpdw
Joined: 21 Mar 2013
Posts: 4
Location: St. Petersburg, Florida
Yes the ammonia did in fact loosen the expander enough to tap it out through the bottom of the stem. This is the first bike that I am attempting to rebuild so this was defiantly a frustrating yet good learning experience. Most-likely will be putting a different stem in because that was ridiculous.
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PostPosted: Sat Mar 23, 2013 9:09 pm Reply with quote
gman309905
Joined: 23 Dec 2012
Posts: 54
Location: Pittsburgh PA.
I'm glad the ammonia worked for you, If your going to replace that stem you need to pay attention to the diameter of whatever stem you choose to replace it because the french steer tube is a slightly smaller diameter than your standard 1 inch threaded.
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PostPosted: Mon Mar 25, 2013 7:45 pm Reply with quote
vanhelmont
Joined: 11 Dec 2007
Posts: 242
Location: Florida
"In this situation, the stems have been inserted too far into the steering tube and are expanded into the "butted" or thicker tubing section at the bottom of the tube. "

Chas, that's a new one on me. How do you know how far is too far?


Jake, the key to avoiding this kind of problem in the future is not to assemble things dry. A little grease where parts join together keeps stuff from getting stuck. Especially where alloy contacts steel they can corrode together and you need the ammonia trick. You would think grease might make the stem loose, but it doesn't. This is more stuff I learned from Sheldon Brown's web pages.

If it's a good stem, if it fits you when not inserted too far! and didn't get damaged in the process of loosening, I don't see why you can't use it again if you want to. It's nice looking. Of course if there's doubt be safe and get a new one.
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Stem Insertion Depth 
PostPosted: Mon Mar 25, 2013 10:46 pm Reply with quote
verktyg
Joined: 14 Jan 2007
Posts: 2628
Location: SF Bay Area
vanhelmont wrote:
"In this situation, the stems have been inserted too far into the steering tube and are expanded into the "butted" or thicker tubing section at the bottom of the tube. "

Chas, that's a new one on me. How do you know how far is too far?

It's primarily a problem on smaller sized frames (19"-21" or 50cm-54cm). Also it's more common with wedge style stems than expander styles.

The wall thickness of a butted steering tube is usually about 2.3mm at the bottom. The top portions is ~1.4mm thick. With an expander style stem it gets more difficult to push the stem into the steerer as you get into the tapered area and the ID gets smaller.




(drawing from Sheldon Brown's website)


The rule of thumb for stem insertion depth is at least 75mm or 3".

There are 2 reasons for that:

The first is to make sure that the stem is strong enough. Cast aluminum alloy stems are not as strong as forged stems (steel stems are 3 times stronger).

Second, the wedge or expander needs to be below the threaded section of the steering tube. The threads create a zone of stress risers where cracks can easily form.





BTW, I've found that most Nitto stems while marked 22.2mm are actually 22.1mm and will fit in many metric steering tubes.

Hope this answers your questions.

_________________
Chas.
SF Bay Area, CA USA
==============
1984 Criterium
1969 TdF
1971 TdF
1974 TdF
1984 TdF x 2 Bikes
1970 SC
1971 SC
1972 SC
1984 SC
1984 Team Pro
1985 Professional
1990s Team Replica
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PostPosted: Tue Mar 26, 2013 10:11 pm Reply with quote
Jakedpdw
Joined: 21 Mar 2013
Posts: 4
Location: St. Petersburg, Florida
I did infact order another stem. Took the old stem and forks up to a higher scale bike shop and they showed me the potential fits. Being a 22.2 mm and all. I don't know the details of the stem but I remember it being a positive incline instead of the "stock" stem's decline. And also i believe this time it is a wedge instead of an expander. I'll post some more details when I get it Thursday.
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death stem? 
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