Hachiroku said:
and the damn thing (89 GL AWD Hatch) is STILL making a loud ticking noise!
Actually, it went away once I ran the car more than a couple miles...
I asked a Subaru tech about this for my aunt's Subie. Mine doesn't make
the ticking noise (until it warms up) but her's does. I thought it
might be something like worn valve lifter but he said that the pistons
are actually looser (more free play) in her model. That noise is the
pistons rattling in the cylinders until it all heats up and expands. I
don't recall what the excuse was for greater piston slap other than
maybe using aluminum in the heads (which has a larger coefficient of
thermal expansion). They want to lower the mass of the heads to improve
fuel efficiency.
To reduce mass, the cylinders are an aluminum compound. Aluminum
expands and contracts more than iron. When the engine is cold, the
aluminum piston is smaller in comparison to it's iron cylinder in the
block. The hollow sounding piston slap occurs most when you start the
engine when stone cold. As the engine heats up with running, the
aluminum head expands more than its iron cylinder so the tolerance
between head and cylinder diminishes with heat up.
I've heard the following used as a test to check for piston slap. First
thing you do after the car has been sitting for many hours, like
overnight, is to start the engine up but let run it for only 15-20
seconds while listening to the sound. Turn off the engine, remove the
spark plugs, squirt in a little engine oil, reinstall the plugs, and
start the engine again and listen. If the problem is cold-starting
piston slap, the noise will be significantly reduced or gone after
adding the oil but only for about another 15-20 seconds (until the oil
has been blown out).
