strange intermittent rattling noise

Hello,
I'm trying to find what causes this sharp intermittent noise, when valves cannot be the cause. I cannot figure out where it is coming from. And I know
noone who would use a stethoscope.
It is especially there when cold, and is quite bright. You can hear it at idle, and even warm, but then it is less bright. Sometimes it is there when accelerating, not all the time, more when cold. When revving up at idle, there's also a short moment of intense rattling, just when the rpm lowers again. The frequency makes me think it is on all cylinders. Someone said it could be a "floating valve". I think I heard that with respect to racing cams. Also I heard piston wear could cause this. It may be possible advance ignition was set at a lower level, would this cause piston wear and this noise ? I heard other wear, bearings, would be lowered through this setting. On the other hand, pushrod shells were the first thing I thought of.
I will try and find more about this on usenet, but I'd appreciate any comments,
Thank you,
Peter
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peter wrote:

Make, model, engine, year?
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Hello,
Possibly more could be said about known engines with specific problems, but I hoped this question could be answered without referring to the model. I have my reasons.
I can say it has an ecu, multipoint injection, sohc and it has four cylinders, 16 valves ( no tappets, but correct valve lash set ) with an aluminium head. I'm using 10W-40 semi synthetic, and the oil is 200 mi, changed with oil filter OEM. It uses oil however, about 0.5 l on 2000 miles.
It is relatively new, 40.000 mi, petrol and has not been worked on yet. Only, it has had some mishaps, like a power test about 3000 mi ago which has loaded the engine far heavier than anytime before. It may have caused problems, but compression is still good. It has also been filled once with 1.5 l too much oil, but without apparent problems. It was drained 250 mi later. It can have overheated when changing coolant running at idle, but it seems the engine still has power.
I wonder if injectors make such loud noises, like while the rpm settles down again after revving up from idle ? For all I know, it could be cheaper to have a replacement engine instead of trying to find the error through rebuilding, but the engine itself could be ok and is new ...
Ask me anything, except please for the make of the car. Sorry for that,
Regards,
Peter
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peter wrote:

What possible reason in usenet anonymity could you have for not giving the make of the car? I'd like to see at least one.
In any event, can you tell us the make of the engine? Displacement? FWD/RWD/AWD/4x4? Transverse or longitudinal? Compression ratio? Recent or long-term issue? Factory set-up or mods? AT or MT? Korean, US, Japenese, German, Swedish, British, or what heritage?
It could be normal detonation issues to a loose shield or pulley somewhere... or an accessory bearing. Buy a stethoscope... we need something to go on here...
Rob
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Hello,
No need for further enquiries ( ;-) or :-{ i don't know yet)
The rattling noise I described is coming from the outlet valves, because of a bad distribution belt which had missed a tooth long ago. Since then I had a car which did not drive like it should.
Thanks for replying !
Peter

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