What could this noise be?

dikidera · Post by **dikidera** » 18 Nov 2023, 10:40

So on my 2.4i NA 140hp engine I started to hear a particular sound when first started. The sound changes with rpm and is metallic in nature and repeats about 3 or 4 times per second at idle. It feels like someone is knocking on the bottom of an old empty canteen although muffled. More noticeable from inside the cabin.

On closer inspection in my opinion, it seems to be coming from the bottom end of the engine and is slightly more audible at 1000rpm.

The only things I can think of aren't good and that is main bearing or rod bearing noise. While the sound feels like it gets quieter with engine Temps, it does not fully disappear becomes just less perceptible and you need to really tune out all noises to hear it.

Suggestions?

Post by **vtl** » 18 Nov 2023, 13:45

dikidera wrote: ↑18 Nov 2023, 10:40 Suggestions?

Make a video.

dikidera · Post by **dikidera** » 18 Nov 2023, 13:47

I will try tomorrow , but it will need processing with Audacity to clear out the frequencies.

adblock · Post by **adblock** » 18 Nov 2023, 13:55

Try placing a large screwdriver on different parts of the engine and sticking your ear to the end of the screwdriver, you will be able to target the noise

We are waiting for your beautiful video, good luck!

dikidera · Post by **dikidera** » 19 Nov 2023, 03:22

This is the sound as heard from the cabin between idle and 1000rpm

You can hear how it's rhythmic knocking.

And here it is outside under the right tyre but at idle

I have too big of a suspect list, the harmonic balancer isn't in quite good condition in my opinion, then we have water pump which I need to replace in the near future, then my other suspects are bearings and this is potentially rod knock or even main bearings, and then detonation and piston slap.

So just doing some basic math, 750 RPM / 60 seconds = 12.5 revolutions per second so the crankshaft is rotating that fast, but you can clearly hear that this rhythmic sound is slower than that and the rhythmic noise if I can trust my counting half that between 5 and 6 knocks per second.
But from what I googled, it's the camshaft that spins 50% slower or half as fast as the crank.

Post by **vtl** » 19 Nov 2023, 08:08

I think it's a VVT hub. This is how my B5244S sounded back in 2011.

It had more funny grinding noises in 1400-1500 RPMs range when intake timing starts to change, yours will probably develop into that soon.

dikidera · Post by **dikidera** » 19 Nov 2023, 11:56

Well I am not sure. The noise could not be pinpointed to the hub when it's occuring. I was very close to it .

Post by **abscate** » 20 Nov 2023, 04:16

Use a hose in your ear to isolate the sound to the nearest few cm to help the ID

Post by **scot850** » 20 Nov 2023, 23:33

Check your water pump bearing.

Neil.

dikidera · Post by **dikidera** » 21 Nov 2023, 09:00

I'll try and isolate the sound via a stethoscope tomorrow, as for the water pump I have a brand new one from INA with gasket ready to be replaced, it's just that the old pump was sealed with gasket maker and not an actual gasket and I think I will have hard time cleaning the old stuff from there.

So, the noise quiets down when the engine warms up. However I then noticed a slight whistling sound at 1000RPM, yeah could be a vac leak, but could also be an exhaust leak or from something else, unfortunately I have no one smart enough near me to operate the pedal at precisely 1000-1200RPM but myself.