crossmember update (more pics..)

[amalventano@sc.rr.com (Allyn)]

to make car go forward, front wheels torque in forward rolling direction,
resulting in engine torquing in rearward direction (i.e. opposite), against
the chassis, as the engine is the thing creating the force on the wheels.

in every scirocco i've owned, the engine has rocked towards the rear when
attempting to launch under load. also, i've had sciroccos with cracked cross
members pop the front mount out of the cup on hard downshifts (the mount
ended up BELOW the cup). on the same cars, if you tried to launch hard, the
radiator would be pushed upward. how, pray tell, can this possibly happen
with said 'downward force vector'.

> my crossmember cracked on the bottom rather than the top? Tension causes
> cracking, not compression (or at least it takes a great deal more
> compression to crack sheet metal in general)

because some previous owner liked to throw it in a lower gear and dump the
clutch to get the engine up to speed. this results in the force which cracks
the bottom of the support.

Al


----- Original Message -----
From: "T. Reed" <treed2@u.washington.edu>
To: "Allyn" <amalventano@sc.rr.com>
Cc: <scirocco-l@scirocco.org>
Sent: Monday, March 03, 2003 11:31 PM
Subject: Re: crossmember update (more pics..)


> Al,
>
> I'm afraid I don't understand. When you step on the gas the engine twists
> axially around the side motor mounts, in the same direction as the wheels.
> If you sit on the drivers side of the car looking at the driver side wheel
> it is turning counterclockwise when the car is going forward. When you
> accelerate, it turns counterclockwise harder and pushes down on the front
> motor mount. The front motor mount is tied in to the crossmember bar, so
> the force vector points straight down.
>
> Perhaps you're thinking that the placement of the inner cv joint relative
> to the axis of rotation at the side motor mounts would make the engine
> twist the opposite direction as the wheels. If this were the case, why is
> my crossmember cracked on the bottom rather than the top? Tension causes
> cracking, not compression (or at least it takes a great deal more
> compression to crack sheet metal in general)
>
> Could you clarify your statement?
>
> Thanks,
>
> -Toby
>
> On Mon, 3 Mar 2003, Allyn wrote:
>
> > > First of all, the force vector acting on the crossmember points
straight
> > > down.
> >
> > umm, during a downshift perhaps, but the major load is in the upward
> > direction, during acceleration. i think this makes your whole
explination
> > backwards (as far as tensile/compressive stresses), but it will work
just
> > the same.
> > Al
> >
> >
>
>
>
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