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[miggy]

Hi All, long time no speak, could someone advise please, when i start the car from cold there seems to be a vauge knocking/pinking from the engine when its slightly revved (1500rpm), sounds as though its from the mid to bottom, knocking is the wrong word really, its more like a pinking, after the car has been revved slightly it goes and never returns, its only from cold starts.
Any ideas would be greatful
Miggy

[miggy]

Just one thing further to the above post, its only been doing this for a week, before then no noise

[The Red Baron]

what engine?. 

[Phil L]

I get exactly the same on my 2003 2.6.  Been doing it for about a year now - a slight knocking in the lower front of the engine and only on cold start up & lasts for around 10 seconds.  Car runs sweet as a nut otherwise.
Phil

[miggy]

what engine?. 

2003 2.6 V6 CDX AUTO

Any ideas??

[miggy]

I get exactly the same on my 2003 2.6.  Been doing it for about a year now - a slight knocking in the lower front of the engine and only on cold start up & lasts for around 10 seconds.  Car runs sweet as a nut otherwise.
Phil

did you get to the bottom of it or is it still doing it

[Phil L]

Still doing it-my friendly mechanic has no idea what it could be and to stress, once it's stopped the car performs normally.
My recommendation is let the car tick over until it stops then drive !
Phil

[miggy]

Still doing it-my friendly mechanic has no idea what it could be and to stress, once it's stopped the car performs normally.
My recommendation is let the car tick over until it stops then drive !
Phil

Same with mine, after a couple of seconds and a slight rev it goes, car runs perfect, strange how its only been happening this past week. Wonder wether it could be the water pump

[pauls]

It sounds like the ghost i have in my car for the last 6 years. I have replaced waterpump,altinator,aux belt and tenshinors ,every time my mate comes to listen it of couse isnt there. I have just had cambelt kit fitted and it still does it. I think it is something to do with one of the pulleys, but due to the car running sweet I have now left well alone. (ps sorry about spelling)

[Webby the Bear]

i have exactly the same thing 

i stuck a load of wynn's lifter fluid in with my last oil change... no improvement.

even though its not due for a year id like to check the timing. having said that common sense says that if the timing is out the noise wouldn't go away 

so other than that no idea 

[Phil L]

I've just seen this on a Cadillac Owners forum that seems to be repeated elsewhere if you do a Google search...
'Re: Rattle/engine knock on cold start up?
What you are experiencing is called piston slap aka "cold carbon rap". There is a carbon build up on the head from granny driving. The piston hits it, causing it to rock on the wrist pin and the skirt "slaps" the cylinder wall. The repair is simple (and fun). Take it out and drive it like you stole it...'
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Any views ?

[miggy]

I've just seen this on a Cadillac Owners forum that seems to be repeated elsewhere if you do a Google search...
'Re: Rattle/engine knock on cold start up?
What you are experiencing is called piston slap aka "cold carbon rap". There is a carbon build up on the head from granny driving. The piston hits it, causing it to rock on the wrist pin and the skirt "slaps" the cylinder wall. The repair is simple (and fun). Take it out and drive it like you stole it...'
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Any views ?

  I dont drive mine like a granny, far from it, she is used daily and i pull the caravan regular

[noel]

have the same problem with mine,and i dont drive like a granny either .
mine sounds like its coming from the cams

[Andy H]

I've just seen this on a Cadillac Owners forum that seems to be repeated elsewhere if you do a Google search...
'Re: Rattle/engine knock on cold start up?
What you are experiencing is called piston slap aka "cold carbon rap". There is a carbon build up on the head from granny driving. The piston hits it, causing it to rock on the wrist pin and the skirt "slaps" the cylinder wall. The repair is simple (and fun). Take it out and drive it like you stole it...'
------------------------
Any views ?

'dangle berries'
Piston slap is caused by over large clearances between piston and cylinder. Thermal expansion of the aluminium pistons is much greater than that of the cast iron cylinders so it doesn't take long after the engine is started for the pistons to expand and reduce the clearance.
Carbon build up in the cylinder head sufficient to strike the top of the piston can occur but I have only seen it in 2 stroke engines or 4 strokes that were consuming prodigious quantities of oil. That much carbon would cause pre-ignition (pinking) before it hit the piston.

If carbon is soft enough to respond to an Italian tune up then it isn't going to be hard enough to cause any audible noises IMO.

Revving the nuts off a cold engine is absolutely the worst thing to do. If it slaps when cold it is a sign that it is worn so the kindest thing to do is to allow it to warm up gently.

[Andy H]

The three most probable causes are piston slap, blowing exhaust gasket or noisy lifters (possibly all three together)

My 2.6 does it. I don't think it is lifters. It only does it for a few seconds, I can make it louder by pressing the throttle and then it stops. (on balance I think it is manifold gaskets)