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Crossmember Bars POLL
Larry,
Have yet to see one of my bars up close?
You are making incorrect assumptions.
The bar is *not* straight across, and was designed with purely vertical
loads in mind, it is weakest in side loads.
http://www.vintagewatercooleds.com/~scirocco/BARINSTALL/barinstall4.JPG
Notice how it follows the V of the crossmember, it has a subtle, but
noticeable V to it. The box steel is also rotated so that its not just
flat across if you notice. We did these minor changes in hopes that it
would maximize the resistance to upward movement given the materials...its
ghetto engineering, but it made sense to us.
A closer shot of the center of the V:
http://www.vintagewatercooleds.com/~scirocco/BARINSTALL/barinstall5.JPG
Side shot:
http://www.vintagewatercooleds.com/~scirocco/BARINSTALL/barinstall8.JPG
Really, it'd be ideal if you could meet up with Potter or someone else in
your area that actually has one and get up and personal with it before you
weigh in on the design of it.
--
Eric
www.vintagewatercooleds.com
1981 Scirocco S (TDI swap project)
1981 Rabbit Truck LX Diesel -FOR SALE-
1990 Corrado TDI -FOR SALE-
1990 Fox Wagon
1991 Cabriolet (2.0 crossflow 8v project)
1994 Jetta GL
Larry Fry said:
>
> So far it looks like the cracking is fairly random.
> Since the front engine mount concentrates it's stress and, more
> importantly,
> its particular TYPE of stress, in an area where the US bumpers have no
> effect, I was afraid this might be the case. Oh, well,...
>
> The problem is that the front motor mount applies a TORSIONAL movement to
> the front crossmember. The crossmember, because of it's large "diameter"
> and short length has a very high resistance to torsion. So, the very thin
> sheet that the crossmember is fabricated of has to flex with the motor
> mount.
> Given enough (torsional) stress, from bad motor mounts, torquey engine,
> etc., the sheet steel is flexed beyond it's ultimate strength. It has no
> recourse but to fail (crack).
> If the torsional stresses were purely lateral (side to side) instead,
> then
> a reinforcing bar such as Eric's would be effective. But they aren't,
> they
> are vertical, which actually creates a combination of torsion and bending
> of
> the crossmember's sheet steel around the motor mount....which is where a
> straight, side-to-side bar (Eric's) is the weakest.
> Imagine no crossmember...just Eric's (don't mean to keep picking on your
> bar, Eric, but it is the only one I know about/of...) bar holding the
> engine's front mount...no crossmember at all; you could move that bar's
> center up and down a significant amount by rocking the engine by hand; a
> three foot long, 1" square tubing just has too little bending strength.
> A much better design would be a trussed bar which would have several
> orders
> of magnitude more resistance to vertical bending. This type of bar was
> suggested by a lister who contacted me off list about this issue. The
> problem is there is precious little room for a trussed bar of sufficient
> size in the engine compartment.
> This is the reason, I believe, (you like that?) that the US-spec bumpers
> are not a factor in the cracking of the crossmember; they don't add to the
> crossmember's material strength.
> Actually, if the crossmember had less torsional strength, we would
> experience less cracking, since the front motor mounts energy would be
> absorbed by the twisting of the whole crossmember and not by the bending
> of
> the thin sheet in the mount area.
>
> How's that, David?
> :)
>
> Larry
> sandiego16v
>
>
> '87 16v Scirocco - had US bumpers, had crack starting by 145k mi...now
> has Euro's and the Saltyweazle bar (crack stopped, handling stiffer)
>
> '87 16v -occo (? car-trailer) - no crossmember :)
>
> '82 DIESEL Scirocco - US bumpers, no cracks (yet!!!), plan on installing
> bar prior to any developing
>
> '87 16v Scirocco (back-up shell) - US bumpers, no cracks, but, the
> front-end was replaced at some point
>
>
>
>
> Hope that helps,
>
> Dan (^^^^ that was my sig....)
>
>
>
> -----Original Message-----
> From: scirocco-l-bounces+danws69=earthlink.net@scirocco.org
> [mailto:scirocco-l-bounces+danws69=earthlink.net@scirocco.org] On Behalf
> Of Larry Fry
> Sent: Tuesday, June 14, 2005 20:30
> To: Brian McGarvey
> Cc: scirocco-l@scirocco.org
> Subject: Re: Crossmember Bars
>
>
>
> Meaning some sort of stress was put on them... Like not changing your
> motormounts for 20yrs..., getting in wrecks, taking the strong a$$ front
> bumper off and replacing it with a decrotive peice of eurotrash. :-)...
> Brian
>
>
>
> Hmmmm. Very interesting point. The Euro bumpers, I mean. Brian may
> have
> something
>
> How about a nice, constructive poll?
>
> How many have Eurobumper?
> How many have US-spec bumpers?
> How many have cracked crossmembers?
> How many don't?
>
> I'll start:
>
> US-spec.......no cracks......220,000miles. (But I just put Eurobumpers
> ON!!!...this may get interesting.)
>
> Larry
> sandiego16v
>
>
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