Re: remove carbon from pistons?

["Michel Drainville" <MDrainville@xxxxxxxxxxx>]

Do it!
I just finished a profile gasket job on my 91 318ic yesterday night, and
since the head had to be removed, I jumped on the occasion to clean the top
of pistons, combustion chamber + valves and also the intake runner tubes. I
was surprised to see how much carbon was on these parts since the car is
only 180000km (108000mi). It's certainly not because I don't rev the
engine, the small 4cyl/16v likes to rev.

Anyways, to remove the carbon, in the combustion chamber, I arranged the
cams so the valves were closed so I could spray some carb cleaner in it.
Then, I brushed with a tooth brush and wiped with a rag. The same thing
applies to the intake runners.

The pistons were another story. First, to keep debris from falling in
between the piston and the cylinder, I followed the suggestion given in the
Haynes manual, which is to bring the piston to TDC, then fill the gap with
white grease or equivalent. First I tried to spray some carb cleaner
slowly, in small shots, so it was absorbed gradually and there was no leak.
After the piston was soaked, I tried the tooth brush trick but the result
were less than acceptable. The carbon was so hard. So I changed my
strategie. I took a small screwdriver ( a plastic or wooden equivalent is
recommended to avoid making scratches on the pistons, but since I had none
available, and I was confident with my dextirity, I took the screwdriver),
and a Shop Vac vacuum, and I started scraping gently the top of the piston
using the shop vac to suck everything. I suggest you don't hold the
screwdriver like a scraper but like a pencil, so more precise movements can
be acheived.

When the piston was done, I cleaned with some carb cleaner, then moved the
piston as low as possible, then wiped the cylinder walls and coated them
with a fresh coat of oil.  I was doing 2 cylinders  at the time since it's
a 4cyl.

Result, everything looks like new, or almost.  And I also found like you
say, that the cylinder walls are still like new! I still can see the
honning pattern on the wall, like a new engine!

Do an oil change and put new BMW antifreeze and enjoy.

Michel Drainville
91 318ic with brand new profile gasket!


PS: I don't know if your like me, but when I disassemble something on my
car, I like to clean the most parts as possible and paint them if they
require it. But this time I went overkill, I polished (shinny) every
aluminum parts that I could get my hand on. So now I have a highly polished
intake manifold, valve cover, front timing cover and thermostat housing.
Looks better than corroded + cosmolined aluminum.
That made a 10hrs job evolved into a many weeks project....