Engine Noise / Loud rattling & tapping

[swhatley82]

Please Help...

During a drive out, I was at high speed and during a downshift the engine noise changed slightly, developing what I can only describe as a rapid tapping noise under acceleration.

As I was on a highway (uk motorway) I gently cruised until eventually stopping at the next junction. The engine on idle/tickover sounded fine, only tapping when pressing the accelerator pedal. Obviously at this point I cut the power and had the NSX towed away

Has anyone experienced this before? Can anyone give me an idea of what these symptoms could be? I have the car booked in with a specialist but it’s 2 weeks away and I’m worried sick
I’ve had my NSX now for 7 years and I’s be gutted for her to let me down now

Thanks guys,
Scott

 

[goldNSX]

Let's hope that it's the LMAs. Quite common. Engine failures are very rare in the NSX.

 

[swhatley82]

Only had these fitted a couple of years ago, the parts were from Science of Speed so I’m not sure. Fingers crossed it’s not so serious

 

[sca037]

I've actually encountered a hollow intermittent 'tapping' sound on a NSX that turned out to be a slightly loose Alternator belt.

If you shined a light on it while running, you could see the oscillations right in time with the noise.

Strange, but true!

 

[Old Guy]

Clearly rev limiting does not work on an overly aggressive down-shift. Was there an oops which resulted in exceeding the red line or was this down-shift 'normal'?

I have only heard one example of sticky LMAs. My recollection is that the noise is most noticeable at idle. Also, I expect that noise due to sticky LMAs would creep up on you rather than appear all of a sudden.

With luck, something just came loose. How old are your engine mounts? Perhaps an aggressive down shift broke a tired motor mount allowing the engine to move causing some noise. Have a look for loose parts / covers. Push on the engine to see if it is at all floppy (I know, pretty hard to do).

Depending on the age of the parts, checking the belt tensioners might be useful; but, I would expect a failing tensioner to be noisy at idle and not be a tapping sound unless it has come loose.