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Old 12-29-2011, 10:04 PM   #1
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Join Date: Jan 2011
Location: colchester, ct
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Car: 1987 IROC-Z28
Engine: some sort of small block
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Rattling noise under valve cover!

Hey Thirdgen, just installed my new hedman headers and exhaust, and all seemed good until after i drove the car around for a while.

Well heres the problem: At an idle, there is a nasty grinding/rattling sound coming from under the valve cover on the drivers side. its just barely loud enough to hear inside the car while driving, but definitely louder with the hood open. its not constant, its on and off every few seconds.
A few searches have told me this could be a timing problem, exhaust leak, valve lash problem, or a broken lifter.
It seems too grinding/mechanical to be an exhaust leak, but does anyone have any information/suggestions on what to check or do? Thanks for any help!
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Old 12-29-2011, 10:08 PM   #2
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Re: Rattling noise under valve cover!

Exhaust leaks near the header flange sound very much like a valve tap EXCEPT that they get louder the more load the engine is put under. An actual valve tap is consistent in volume regardless of engine load.
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Old 12-29-2011, 10:18 PM   #3
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Re: Rattling noise under valve cover!

ok, so then by simply pressing the throttle under the hood i should be able to tell if its an exhaust leak for sure? i thought i got all the bolts torqued down, but ill double check for sure now
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Old 12-29-2011, 10:24 PM   #4
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Re: Rattling noise under valve cover!

If it's a flange leak you will know the instant you step on the gas to pull away from your driveway. It'll get louder as soon as you put the engine under load. When you let off the pedal and coast down for the stop sign at the end of your block the sound will almost completely disappear. At idle in gear it will be slightly to moderatly noticable.
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Old 12-29-2011, 10:36 PM   #5
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Re: Rattling noise under valve cover!

hmm now that doesnt really sound like what im experiencing, this is really only noticeable at an idle. it sounds almost like someone dropped change or marbles under the valve cover, that kind of rattling/crunching noise. its strange because its not horribly loud, or consistent. doesnt seem to affect performance either
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Old 12-29-2011, 10:51 PM   #6
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Re: Rattling noise under valve cover!

What else did you do to the engine around the time you installed the new exhaust system? If it's not exhaust-related you have to ask why something else would have chosen that moment in time to become a problem.
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Old 12-29-2011, 11:00 PM   #7
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Re: Rattling noise under valve cover!

thats very true, aside from the exhaust i have not touched much else on the engine. i guess im just paranoid, whenever i hear strange noises coming from anywhere near my engine i panic a little.
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Old 12-29-2011, 11:43 PM   #8
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Re: Rattling noise under valve cover!

Pull the valve cover and look at it.
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Old 12-30-2011, 12:46 AM   #9
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Re: Rattling noise under valve cover!

Sounds like one of the pushrods is slapping a rocker arm. I had a lifter go bad one time and it allowed the pushrod to drop and slap the rocker. Was fine at speed but loud as hell as idle. Best thing to do is like Infernal Vortex said and pull the valve cover and check it. What ever it is, you want to fix it before it causes more damage/issues.
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Old 12-31-2011, 04:21 PM   #10
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Re: Rattling noise under valve cover!

huh wow did i feel dumb today, went to go grab the breather on the valve cover and it was shaking like crazy! i replaced the pcv valve and that solved it, even made the car idle better
thank god it was something easy rather than something expensive, thanks for the help again guys!
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Old 12-31-2011, 04:21 PM
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