To most auto enthusiasts, nothing sounds sweeter than the high-powered revs of a racing car or the sound of a modified car?s exhaust. It?s also the sort of sound that elicits appreciation from the most unexpected quarters ? my 70-year-old mother for instance, who had me totally thrown one night while I was going pedal to the metal through the gears in the family Padmini in Ballygunge ? ?Nice sound?, she said.

In fact the best thing you can do for your car is to listen to it. This can prove useful when one has to diagnose a fault ? especially an engine one. It can also be fun trying to guess what the problem is ? a blown head gasket or timing off ? just by listening to the sound the engine is making. Of course, it?s not as easy as it looks ? or sounds ? and there is a very good chance of the diagnosis being wrong. But if you?re a DIY type of guy or girl, then there?s no harm in trying to diagnose the fault on your own.

I recall a time when our family car, the aforementioned Padmini, developed a strange high-pitched whine that occurred only when the car was in motion and in gear, but not while stationary with the engine running. Upon inspection, nothing wrong was found with the drivetrain, wheel bearings or any other bearings. Nothing operated at that speed to give off that kind of a whine. It didn?t come from the engine bay nor from the passenger cabin or boot. All was revealed one day, when the speedometer needle started quivering when the whine was as loud as ever. Suddenly it stopped working. And the whine stopped as well. The little speedometer cable pinion at the instrument end had been the culprit all along.

When diagnosing engine noises, you have to rely on your ears. The job can be made easier by purchasing a stethoscope but if you can?t get your hands on one, there are two simple but crude options that can work as well.

The first option is to use a screwdriver with a long shaft. Put the handle end to the ear and apply the tip of the shaft to the noise source. The other alternative is to use a hose and stick one end in one?s ear. Of course, neither of these methods will be as accurate as a real stethoscope.

Step one is to check the accessories like the alternator, power steering pump and AC compressor. If the noise seems to be emanating from any of these, isolate it by taking the belt off. If the noise remains, the problem is elsewhere. You need to isolate the source of the noise in order to make an accurate diagnosis.

If the engine is carburated, check and see if it has a mechanical fuel pump. After protecting yourself from being burnt by a hot engine part, put your hand on it ? a noisy pump can be felt.

Use the stethoscope to track the noise down. Trained mechanics can actually say which piston is slapping. DIY people are also pretty good at it though every one really starts out as a novice. So don?t lose heart. Keep trying if you fail.

As you practise, you will get better at differentiating between the several noises a mechanical device like an engine makes. For example, noise from the engine cylinders can be diagnosed better once the problematic cylinder has been located. Once this has been done, short the cylinder plug wires. The traditional Indian roadside mechanic?s way of doing this is to use a screw driver blade and create a short circuit between the plug top and a common grounding point. But a better way is to use an insulated wire or a low-voltage test light. If the noise changes, it is likely that it is coming from the bottom end.

If the sound does not change, then the noise could be due to the piston slapping sideways against the cylinder wall. There is a test to determine this and it is particularly applicable to engines with aluminium pistons and iron blocks. When the engine is cold, on starting, it will make a hollow knocking noise. This is because there is a gap between the aluminium piston and the cylinder as the bores are different. However, once the engine warms up a bit, the piston expands and takes up the extra clearance and the noise goes away.

One can test an engine for the absence or presence of piston slap. Start up the cold engine, run it for 15-20 seconds and then shut it down. Take the plugs out and squirt a little engine oil into each cylinder. Put the plugs back and restart the engine. This will make the engine quiet but only initially, if piston slap is present. The noise returns as oil film breaks up and the piston starts slapping against the cylinder wall.

This is only the tip of the iceberg as far as fault diagnosis through noise goes. Almost every moving component in a car makes a noise, though cars with good NVH treatment are very quiet. However, there is satisfaction in knowing that your diagnosis was bang-on correct. And hey, even if it wasn?t, there?s always next time!

My dream car

Jimmy Tangree
radio jockey

I’m a person with an adventurous streak and so I’m always drawn to speed and good looks. That’s why my fantasy on wheels has to be the Ferrari. It’s got the looks and of course, one mean engine under its hood. I can’t remember the exact model number but about two years ago, Ferrari launched a model with receding headlights. That’s the one I’d love to have and it would have to be in my favourite colour — flaming red.

While the Ferrari is my dream car, my dream bike would be the Honda CBR or a Kawasaki Ninja. Both of these score on speed, looks and the safety aspect. I’d love to zip down Red Road on one of these at 200 kmph. What a rush!

In fact that’s something I used to do in the 80s when I had an MBX 50cc bike, which came with six gears, an LC engine and a top speed of 120 kmph. Over the years I’ve also owned a Honda VT250F and a Yamaha DTLC.