320iS modifications
My 320iS has undergone several modifications, some of them quite simple.
As they can help you improve your car, here are some details:
E36 M3 3.2 (S52) timing
chain tensioner
For all early BMW Motorsport engines, BMW used the
same tensioner. So these cars all have the same unit
fitted:
* E23 745i South Africa (M88)
* E24 M6/M635Csi (M88)
* E26 M1 (M88)
* E28 M5 (M88)
* E30 320iS (S14)
* E30 M3 2.3/2.5 (S14)
* E34 M5 3.6/3.8 (S38)
* E36 M3 3.0 (S50)
Due to a relatively soft spring they really need some internal oil pressure to
function right. This means the timing chain is prone to some rattling at cold
starts. As the chain gets some free play this can also cause some cogwheel
wear.
The S52 tensioner has a stronger spring and has a telescopic
design making it more closed. These differences ensure more pre-tension at cold
starts and most times takes all rattles away, both at cold starts and at high
revs. The BMW part # is 11 31 1 405 081.
Note: if it doesn’t take away the rattles, it is about time to inspect
your chain and cogwheels as they can be worn. If you leave that unattended the
chain might skip one day whcich can cause a major engine damage.
Throttle cable clip(s)
After stepping on the accelerator fiercely, the throttle cable jacket can pop
out of its holder on top of the airbox. With this
simple steel clip this can be prevented. It costs close to nothing and is
fitted within seconds.
BMW # 35 40 1 165 393. If your car has cruise control
you need two.
Suspension
The 320iS basically shares most parts with the euro 320i and 325i rather than
the M3, it also has the 4 stud wheels. My 320iS was on OEM BMW/Boge shocks all round when I bought it. Good stuff but I
now fitted even better Bilstein Sprints.
The springs were the original Sportfahrwerk
units. They lower the car only a little bit, my guess is about 12-
The front struts are equipped with new top bearings, OEM stuff. The rear
stabilizer links didn't look too good and were replaced by new aluminium
examples.
The rear shock mounts/bushings: the original ones look a bit thin. The
E36 version fits perfectly and is larger and stiffer. Part #
33 52 1 137 972. I recently heard that the E46 convertible mounts also
fit and are even stiffer. And you can also fit Group N bushings (part # 33 31 1
417 247) although I've never tested the improvement in stiffness, but they are
known to pass on more suspension/road noise.
The most recent mods:
I fitted the E30 M3 quick steering rack which was a straight swap)
Pro-Auto solid and eccentric front control arm
bushings 
(click for enlargement, link to Pro Auto
website on 320iS main page), new front sway bar bushings. The new control arm bushes were a
tremendous improvement in feel, steering and braking!
Last but not least I fitted the E24 gearbox bushings. Takes quite some ‘stock’ free play out
of the driveline (stock bushes are really soft even new) and makes shifting way
smoother!
'iS' deep front spoiler
This is an upgrade that doesn't look too aggressive, especially if you paint it
black like the original spoiler, like I did. It fits in the same clips and
requires no further changes. It improves high speed stability.
Air intake
There are some well known upgrades here, like:
* Evo III lower air filter box, improves air flow
towards the original air flow meter
* Sports intake filter (K&N, Green, …): replaces
the OEM panel filter. More sporty sound, slightly more mid-range torque, fitted
a K&N myself
* Open air intake filter (like K&N 57i), also improves air flow
towards the original air flow meter, but is more vulnerable to humidity and
dust
* Carbon fibre airbox (as used in Germanys DTM).
Produces a beautiful roar from the intake and improves air flow and torque
tremendously. But... it also requires a different air flow meter combined with
different engine management, like Alpha N. Expensive though! I heard some
people are working on a carbon fibre airbox that fits
the factory setup, so it uses the regular air flow meter. I’ll keep you posted
on that.
Update: currently I am running a stock air filter after stories about
K&N letting through more dust. With re-adjustment of the engine, there
shouldn’t be much of a difference.
Brakes
Here we also see the parts we know from the Euro 320i/325i. Apart from a
rebuild they are stock. The OEM rotors are supplied by Até.
At the front I fitted Até Powerdisc
rotors. They are the same rotors as OEM equipment, but with oval slots. Current
pads are OEM BMW.
There are several E30 big brake kits, but they all require
Strut braces
I used to have a three-piece single tube front brace, but I recently replaced
it by a single piece dual tube example. They seem hard to find but Dutch based Improve
Tuning can help you out as they helped me out.
Haven't tried a rear brace yet.
Oil leaks
The oil filter manifold is known to leak some engine
oil. The oil thermostat cap is most likely to be the cause. I replaced the cap
and its seal, but the oil pressure sender was also leaking. It is the same
sender as in most contemporary BMW’s and as far as I know it is a common
problem.
Ignition
OEM spark plug cables, rotor and distributor are supplied by Beru-Bremi.
Wear on rotor and distributor is easy to recognise. But as the spark plug
cables are fitted in a narrow harness they tend to affect each other inside.
Open the housing at least once a year for a check. The cables can be ordered
through any Beru-Bremi reseller and come as a
complete set, complete with the rubber cap over the ignition coil (even marked
with BMW logo) and the wiring harness.
BMW only recommends Bosch 'Super 3' X5DTC spark plugs so there was no doubt for
me there. Fit them with a torque wrench at abt 23Nm.
Engine bay work – replacing hoses
After the third coolant hose was ripped
apart I decided to do something to prevent this from happening in the near
future. The original coolant and fuel hoses were still in the car so it was
about time to replace them. Since it were the hoses to
radiator and thermostat that fell apart I reckoned the engine mounts could have
something to do with it as well. I replaced these first, just OEM E30 M3 stuff.
In the near future I will replace the gearbox bracket bushings as well,
probably by the slightly stiffer E24 6-series examples.
I removed the air filter housing with air
flow meter, the air accumulator and the alternator to get some room. After that
all coolant and fuel hoses in the engine bay were replaced.
Photos: In the
process
Thermostat
housing rebuild with new switches and hoses
New OEM fuel hoses fitted (behind them you can
clearly see one of the old coolant hoses coming from the cylinder head, marked
with build year 87. It was replaced of course)
And when in