Engine noise at 3800 revs

[ESDavey]

when the engine is under load (ie 3rd gear) I have started to get an engine rattle / vibration / tommy gun sound at 3800 revs approx. I can sense this in 2nd gear but very slight. It appears to be on the left side.

Engine has done 24k, pulls well and very smooth. I have noticed that 3800 in 5th is my normal cruising speed but think thats a coincidence

Any ideas ? I'm thinking valve guide, tappet, etc.

[cinquecento]

My 2 cents..Could it be pinking/pinging under load?. You could check your static advance abt 10 degrees would be around right at idle.

[ESDavey]

No, it a metallic rattatatat sound. Maybe something vibrating at the 3800 frequency ??

[GreenV8S]

Does it happen under part throttle and/or full throttle conditions?

[ESDavey]

Both .. even with steady progression through the rev range. The more I think about this, the more I'm thinking vibration of some kind.

[jeffsy]

Hmmmm..fwiw... Id get it checked out as I experienced a similar metallic 'chatter' on my old engine before it melted a few years ago. I too thought it was some kind of frequency/vibration thing (maybe even the bonnet stay coming loose).

Maybe a coincidence, maybe not...

Graham

[GreenV8S]

ESDavey said:

Both .. even with steady progression through the rev range. The more I think about this, the more I'm thinking vibration of some kind.

That's good news, because if it happens at part throttle you can pretty much rule out detonation. I think you're on the right lines looking for something hitting resonance, and the exhaust is a likely suspect. Any contact anywhere along the exhaust can produce strange noises elsewhere as the sound carries through the metalwork.

[ESDavey]

Good news - the vibration has gone ! (maybe something fell off or that rogue screw driver/socket/clip/hammer/beer can has rattled free !!)

..... which makes me think that all of the advice about driving these machines is 100% correct. I did a track day at Brands yesterday and the car now idles properly, runs smoothly and feels REALLY good.

[LordGrover]

Good news.
I think you'd better start touching wood after a statement like that though.