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Old 01-22-2008, 01:28 PM
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Ford 4.6 knocking.

My older brother has a 1998 Ford F150, its got around 160,000 miles on it. 4.6 liter V8 thats been well mantained. It's developed a knock on the drivers side valve train. the noise traced with a mechanics stethiscope is deep and loud with no echo on the very front of the valve cover, the timing chain cover seems to have a echo to it, as does the rear of the valve cover, so the source is at the very front. I don't know much about OHC engines but I know how they work. Funny thing is about this is you can shut it off at any engine temp, then restart after a minute, theres no noise, after a solid minute has went by the noise starts to slowly come back, it starts as a light tap, then goes back into sounding almost like a diesel. We removed the serpentine belt to make sure we eliminated any other noise possibility. What usually wears out in these engines valvetrain wise? I know the timing chains have tensioners, and the rockers are of roller design, but I know rollers can wear out. Is the rocker or rockers shot? possible valve guide going south? Any help is appreciated.

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Old 01-22-2008, 03:04 PM
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Although I am a Ford guy I have limited Mod motor experience. I do however keep up with all things Ford and I believe that the cam chain tensioners need replacement periodicly. From the description you've given I would guess that to be the problem. Datsuns had a similar problem in the 510 days.
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Old 01-22-2008, 06:59 PM
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the 4.6 in my 97 Bird is still very quiet after 200,000+mi

Altho it has begun to use coolant---dunno where it is going
and from the day I bought it----even Ford cannot get the check engine light to stay off.

But----this is "apples to fruitcake" comparison, and mine was never used to haul anything but people and groceries. Pretty sure the pick-up won't fall into that catagory.
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Old 01-23-2008, 07:14 PM
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Worn chain that is allowing the cams to move back and forth due to the loosness of the chain. We have seen this on a few v6 overhead cams. The last one we did was on a Nissan with the distributor in the front middle and it sounded just like the distributor was junk. Very hard loud knock.
I would take a good look at the chain. If there is any slack in the section between the two cams this is most likely the issue.
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Old 01-23-2008, 07:16 PM
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Also on those Fords if the tensioner start breaking up the pieces like to head straight into the oil pump. We have seen this a few times on exploders (explorers).
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