Hi Jim,

Don't want to sound like I'm belaboring the issue, but
At 10:47 AM 12/29/2011, Jim Felder wrote:
>Sorry, but I can't see that one form of mechanical force is superior
>to another, all other things being equal (like the durability
>argument that's been proposed... yes, zip ties could disintegrate,
>but clips could rust. In fact, neither is true).

I'm not concerned about either one.

>I'm not arguing against the clips, David. In fact I have used them
>on three out of the four heater boxes I have done. But are they
>better than zip ties? No. You can't tell once the box is in the car.
>I'm just saying that there is no reason to dissuade anyone from
>using any alternative method that actually meets reasonably high
>standards, equal to or better than what was used originally.

I'm a huge fan of zip ties, been using them since they were
invented.  My issue with them here is twofold: first, splitting the
tabs with a knife is a bloody nuisance and can wreck the tabs - I've
done it.  They're designed for single use.  Much easier to simply saw
them off flush.  Second, I'm concerned about stress concentrations in
the plastic from using fasteners with that little area.  This may
well be overcaution, but I've seen an awful lot of plastics failures
resulting from treating the stuff as though it was metal - look at
the tabs on the Vanagon instrument panel for an example, and the way
the screws break out of the corners of the tach and speedo
mounts.  Those failures are caused by the manufacturer failing to
understand how plastic reacts to stress over time.  I could point you
to a whole chapter in the big plastics industry annual handbook from
that same era talking about that exact problem and scolding
mechanical engineers for not understanding their materials (well, I
no longer have the book and forget what it's called, so I guess I
can't actually).  Anyway I've taken that to heart and had good
success with plastics as a result of that understanding.  I'm very
reluctant to use a plastic fastening with less clamping area than the
original for that reason.

>Last week, I chimed in in support of cork valve cover gaskets when
>someone stated that their mechanic said that they "fail often." This
>is creating a problem where none exists, and it's not fair to people
>trying to learn to work on these old vehicles.

Why on earth should cork valve cover gaskets fail, unless you re-use
them too many times or they come apart when you take the cover
off?  You're supposed to use new ones anyway...not that I generally have.

Cheers,
d