<E28> Sloppy steering, and spark plug question

[Patrick Burns <patrick@xxxxxxxxxxx>]

(Apologies to Mark Holbrook, who has to read the same thing twice now.
:)

So my new 179k mile and 14 year old 528e had really sloppy steering.
The ball joints of the control arms and tie rods all checke dout. The
idler arm bushing was worn out, allowing the passenger tire to flop
around in relation to the steering arm and driver's side tire. Didn't
see just the bushing anywhere. New idler arms are $40 at discount mail
order houses. I don't even want to know how much they cost at the
dealer, though I suspect about $60 or so. Since I had some Delrin left
from the shifter project...

The steel outer sleeve of the bushing had rusted a bit on the I.D.
(bearing surface). I tried glass beading it, but the rust was pretty
determined to stay put, so I chucked it up in the lathe (still pressed
into the idler arm so it would be in the same shape and experiencing
the same forces as it would in use... sort of like using a torque
plate to hone a block... good thing the lathe is a big one because the
arm barely cleared the ways, and the whole damned (really really
heavy) machine was shaking around from having five pounds of steel
whipping around off center) and bored it out. Got to clean metal, then
went to the connecting rod hone and cleaned up what amounts to
threads. Nice clean bore, all straight and round and stuff. Went back
to the lathe with a rod of Delrin. Drilled out the center, using a
Jacob's chuck in the end stock and a drill bit just slightly smaller
than what I needed. Finished the I.D. sizing by boring it out until it
was just a tiny bit (0.2mm) undersize in relation to the steel pivot
thingy in the middle, which gets clamped in the sheet metal box on the
subframe, for a nice tight interference fit. Put a slight chamfer on
the end to facilitate pressing the steel pivot into the Delrin rod.
Pressed the steel into the Delrin, swelling the O.D. of the Delrin.
Turned it down until it was just _barely_ larger (0.05mm) than the
I.D. of the steel sleeve. Tight press fit of the Delrin on the steel
pivot so they don't move in relation to one another. Loose press fit
of the Delrin in the outer sleeve so they slide in relation to one
another, but without any slop, and sort of preloading the bushing so
it doesn't flop around much under the forces to which it will be
subjected. Pressed it together. Can't quite turn it with my fingers,
but once it's mounted up in the car, there's just a little bit of
friction. Can't even feel it at the steering wheel. Used valve spring
seat shims to act as thrust bearing surfaces and locate the idler arm
vertically. Better than new. No slop. Hey, who thought up putting
rubber in steering linkages anyway!? Man...

Adjusted the steering box free play too. Didn't have to tighten it
much, but it made a difference. It sure does drive nice now. :) Next
is the 750i thrust bushings. How wide are they stock? Will they press
into the E28 thrust arms with no modification? Do I have to narrow the
outer sleeve to fit in the frame, or just the center part? As you can
tell, I don't have one handy for comparison...

So what's the deal on spark plugs for this thing anyway? Do the Bosch
WR9LS plugs actually work any better than (much cheaper) Bosch WR9LP
or (much, much cheaper) a plain old NGK? Is it just a longevity issue?
I'm not averse to replacing the plugs four times as often if they cost
1/5 as much...

------------------------------