Crossmember Bars POLL

[peter at thescirocco.com (Peter)]

$117 does seem kinda high...

You really shouldn't bench test VW starters like that, they need the trans
to support the end of the spindle, so the windings don't get damaged.

I usually hold them, or bolt them, to a spare trans to test them. I recently
cut up an auto trans and made up a test jig, but a spare trans works just as
well. 


Peter
http://thescirocco.com/

Please! Include the previous text in your reply...

-----Original Message-----
From: scirocco-l-bounces+peter=thescirocco.com@scirocco.org
[mailto:scirocco-l-bounces+peter=thescirocco.com@scirocco.org] On Behalf Of
Chris Bennett
Sent: Saturday, June 18, 2005 8:50 PM
To: Nate Lowe
Cc: scirocco-l@scirocco.org
Subject: Re: Crossmember Bars POLL

I got under the 85 with the 16v conversion today. The starter apparently has
died. (good charge on the battery, click click with the ignition) I thought
about trying to push start it but I have had two knee surgeries in the last
year and I don't push like I used to... I removed the starter and performed
the INFAMOUS "mexican jumping starter dance" (that would be a set of jumper
cables on the starter and a jumper...er I mean wire to test to see if the
bendix works or not. I forgot to put my foot on it and scared the shit out
of myself.) The bendix extends and it spins very weakly sometimes not at
all. Jumper wire gets REALLY damn hot really damn quick. So I decided to end
amatuer hour and take it to a FLAPS. I walk in and dude asked me if that was
the turbo from my scirocco. I realized at that point that I was in deep
shit. After discovering what it was he goes to the test bench and punches in
the the code and tells me that he can't test it. So I was like COME ON
MAN!!! There's only four wires... So he hooks up the +12v and the two
smaller wires, (ignition and something else--don't remember off the top of
my head.) and tells the thing to go... As politely as possible I remind
supergenius that it needs a ground. You know how dem dere "turbo's" act when
thays ain't properly grounded.
 So once grounded he hits the button and the bendix extends once again and
then the machine tells us that it is a bad starter. So I still don't have a
warm fuzzy since this guy told me he couldn't test it and he didn't know
what the hell it was, so I asked him to go and get a new one off the shelf
and prove that the machine is doing what it's supposed to. Well he wasn't
"allowed" to do that until I pay for it. So I was like fine, what's the
damage?
 $117 plus a $60 core. I think I stared at him in disbelief for a good 12
seconds. I am thinking: WHY THE FUCK WOULD YOU CHARGE ME A CORE WHEN I HAVE
THE DAMNED THING SITTING IN FRONT OF YOU?!? and then WHY THE FUCK WOULD I
PAY THAT MUCH FOR A STARTER?!? I resisted the urge to shove the starter up
his ass, thanked him with all the nice I could muster, and left. I don't
have that kind of money anyway.
 Anyhow, here's the bottom line of this story. While I was under the car I
took a real hard look at the cross member and I do not see any cracks. 
There's a lot of sludge and crap and I wiped it off the best I could but I
still didn't see anything. I was looking from the bottom where the two bolt
for the fwd mount plate are, and didn't see anything. So for the time being
I am safe or is there somewhere else I should look?
 Chris

 On 6/18/05, Nate Lowe <nlowe79@gmail.com> wrote: 
> 
> On 6/18/05, Allyn <amalventano1@tds.net> wrote:
> > i knew that one was coming. the way this bar works is similar to 
> > that
> bar
> > you see the big-ass weight lifters using on tv. the guy lifts the 
> > bar
> near
> > the center, with massive weight at either end. these bars get used 
> > for
> years
> > and years. it may weaken and bend easier over time (yield strength / 
> > ultimate strength lowers as it is fatigued), but you never see one 
> > just snap. the failure mode in this case is to become more bendable, 
> > not to brittle fracture.
> 
> Interesting analogy, but I don't think it's completely applicable. I 
> don't know anything about those bars used in weightlifting, but I do 
> konw what you're talking about. The thing is, those bars can't last 
> forever, they will break if they are used too much. The same goes for 
> the crossmember bar (well, maybe not, if you crunch the numbers it 
> very well come out that the bar is never pushed passed the fatigue 
> limit). I will also add another quote from my textbook: "Fatigure 
> failure is brittlelike in nature even in normally ductile metals, in 
> that there is very little, if any, gross plastic deformation 
> associated with failure. The process occurs by the initiation and 
> propegation of cracks, and ordinarily the fracture surface is 
> perpendicular to the direction of an applied tensile stress." That 
> sounds like the cracks people are seeing in their crossmembers. I have 
> to admit that I have never seen one in person, but I have seen 
> pictures and those pictures seem to fit what I'm thinking..
> 
> > > Do you think the crossmember is breaking due to being pushed past 
> > > it's yeild strength?
> >
> > yes, this is the exact reason. the metal in the cross member is 
> > somewhat hardened steel. my guess is that it is hardened enough such 
> > that the RTT
> is
> > near ambient temperatures. if you've ever seen the cracks we speak 
> > of,
> they
> > are jagged and sharp at the edges. basically brittle fracture. 
> > brittle fracture is 'sudden, catastrophic failure of a metal under 
> > tensile
> stress
> > with little to no plastic deformation (bending)'. it requires a
> pre-existing
> > flaw (small crack, nick in the metal, etc). when a crack propogates 
> > in
> this
> > mode, the only way to stop it from propogating is to stop drill it. 
> > its basically the same as a crack in glass. the stresses are 
> > amplified
> greatly
> > at the leading edge of the crack, so it spreads that much easier.
> 
> You are right in that once a crack is formed it will spread much, 
> much, much easier (I can't emphsize enough how easy it is for a crack 
> to spread once it's there). Again, the problem with your reasoning 
> here is that you aren't considering fatigue, you are only considering 
> brittle fracture alone. Lastly, I don't know what you mean by RTT, 
> I've never seen that abbreviation before and I'd like to know what it 
> means. I don't think it will change my opnion on this though.
> I also left my responce in here (noted by the double arrows (whatever 
> they're called) because I think it's necessary to understand the 
> conversation if you havn't been reading every post. Allyn's words are 
> noted by the single arrow.
> 
> > > I don't, because if that was the case drilling holes would do no 
> > > good and the entire crossmember would break in half before you 
> > > even noticed the cracks. The crossmember is cracking due to 
> > > fatigue.
> >
> > easy stop to that argument is the fact that only the _newer_ (~>85)
> cross
> > members are the ones that are cracking. wouldnt you think that a 
> > similar designed piece in a 30 year old scirocco would have more 
> > fatigue than
> that
> > of a 15 year old one? mileage and horsepower dont seem to have much 
> > of
> an
> > impact on it either. from my words above - i think vw hardened this
> steel a
> > bit more or used a different mix that had a lower fracture toughness 
> > /
> RTT.
> > i also believe that the cracks don't occur unles some major shock 
> > type stresses are applied to the member (i.e. accident, bad side 
> > mounts,
> etc).
> 
> I think that there are a couple different things that contribute to 
> this point. First, I'd agree that there was most likely a change in 
> the material used for the crossmember sometime during the mid 80's.
> You must also consider that a 30 year old scirocco didn't have the 
> horsepower of a 16v out of the box. I thought, from what I've read, 
> that most people with this problem had 16v versions (not swapped, but 
> real 16v's). I may be wrong on this, that's just the impression I got.
> It would be intersting to see who had cracks, when they started, and 
> what had been done to the motor over the car's life. I'm still 
> inclined to believe the cracks are from fatigue though.
> 
> > > Good, now I know how thick the plate is. It didn't look that thick 
> > > in the pictures. But if you look at the geometry of that plate, 
> > > the
> >
> > whoa there, dont quote me on it :) its either 1/4 or 3/16. im going 
> > on eyeball gauge only.
> 
> Oh, I thought you had the exact measurement. I won't quote you on it 
> then ;). I'd lean toward the 3/16 if not 1/8, but that's just eyeball 
> from me too, and from pictures only at that. This is nothing to argue 
> about since the designer is on the list and can just tell us what it 
> is.
> 
> > gotta run, party at my place :)
> > p.s. no flamage here, just opinions, backed by some navy training.
> > Al
> 
> Have fun with your party. No flamage from me either. I openly admit 
> what I'm saying is opinion and can be proven wrong. I don't mind at 
> all if someone points out where my reasoning is flawed, it certainly 
> won't be the first time :) But what I would like to say is that my 
> main focus here is that the bar hasn't gone through any rigorous 
> testing so nobody can say for sure how much it helps (and testing can 
> be as simple as doing a few calculations to see what it will 
> withstand. Granted some assumptions will need to be made, but that's 
> engineering). That said, I'd suspect that any car without any existing 
> cracks would probably be fine with this bar, it's the cars who already 
> have cracks that I really question. That is because of the major loss 
> of toughness (engineering meaning of thoughness: resistance to 
> fracture) for those unfortunate cars that already have cracks.
> Nate
> 
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