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Discussion Starter · #1 ·
I have a knocking sound on my V6 only on the first startup.Thought it was the airfilter box,but with bonnet open you can hear its coming from the engine.Its there for a few seconds,but its a hard knocking sound.This is a rebuild motor,it also smokes alot when driving hard.Any suggestion on the sound?
 

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Mine knocks similarly but only under load and is quiet on start-up. I suspect a main bearing. Maybe yours is a big-end? Or piston slap?

Piston slap is common on incorrectly rebuilt motors if the piston to bore clearance is excessive and the pistons haven't expanded yet. It also leads to high oil consumption and excessive blow-by. Open the oil filler cap at idle on cold start and check to see if it is blowing any exhaust fumes from there. This would definitely indicate excessive bore wear or excassive machining of the bores.
 

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If you fast idle on start up ag 1500rpm-2000 and no knock then you can eliminate piston slap . It's not rule of thumb . Some times cam belts if too loose can hit the bottom cover ( aluminium cover around crank) and believe it or not make knocking sound when cold . How long does it take for oil pressure to get up ?
 

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Discussion Starter · #4 ·
@Ian,I checked now with oil filler cap off,there is no smoke.

@Kevin,my car does not have a oil pressure gauge.

With my hand on the intake I can feel the knock when it is there.
 
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