So been to view an engine to replace my knackered one!

Sounded perfect on idle and perfect above say 1500rpm but it's got a slight knocking/rattling at about 100-200rpm above idle.


So I've left it and said I'll get a second opinion and go back the weekend.

Anything common or is this a tricky one??

 

Was it stone cold when you started it and heard it running? F20's do suffer from piston slap when cold due to the fact they're a "forged" engine. Mine sounds a bit rattly at and around idle when it's cold but it's fine once it's warmed up.

Other than that i'd be checking the obvious tell tale things like oil colour and level to get a rough indication of engine care. It may or may not tell you anything but if it's black and grotty looking then it indicates to me that it's probably not been looked after all that well.

Tricky to say without hearing anything though.

 

If it's black it may indicate the oil is doing its job, and if golden it may indicate a fresh oil change to cover something up

I've not heard of piston slap due to it being forged? Only forged part are the Pistons. Timing chain tensions can cause a slight rattle, lots of videos on here for that.

A nock / rattle is not a good sign though.

 

Probably valve lash clearance
would do a comp test if i was buying

 

That's also prime time RPM territory for heat shield rattles! Could be something as simple as that, so see if you can isolate where the noise is coming from.