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Old 05-23-2014, 07:27 PM   #1
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ive got a 1990 cavalier 2.8 v6 auto. the other day i shut it off for a few seconds and when i restarted it it had what sounds like a loud rod knock. this doesnt make sence, it never gave any indications of a rod brng noise. good oil pres, never a rod noise at start up and only 60k miles. its a fast knock (crank speed not cam speed) this is a loud knock , it sounds vary mechanical but someone told me there car did the same thing and it turned out to be a cam sencer. my check eng light is not on. anybody got any ideas what it could be ( other than a rod). thanks for any help.
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Old 05-23-2014, 10:34 PM   #2
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Your car doesn't have a cam sensor....

Even though it'* only got 60K miles on it, it is a 24 year old engine....

So this noise just started out of the blue, and hasn't gone away? Does it get louder with higher revs?
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Old 05-24-2014, 01:02 AM   #3
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ya it kinda gets louder. funny thing is it changed pitch a couple of times, like something was moving inside, like a broken rocker arm. i put a piece of garden hose to my ear and held it to different places on the engine. it was loudest under one end of one of the valve covers. it sounds to fast for aa top end prob though. and of course it has to be under the one thats hard to get off.i geuss ill take it off on the wknd. it really does sound like a rod though . but all i did was start it. no abuse, ever no bottom end noise at all... then knock knock, damb, it got such good mpg to. lol. what do you think?
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Old 05-24-2014, 09:39 AM   #4
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How has this car been driven over the years? Lots of short trips with the engine never really getting up to operating temperature for very long? I ask because your symptoms sound suspiciously similar to one encountered by a neighbor of mine many moons ago. He had a cutlass with a V-8 that had never been abused and suddenly it developed a hellacious noise similar to the one you're describing. He had the engine torn down to find out there was nothing wrong other than a chunk of carbon had come loose from one of the heads and it was probably causing interference with valve operation. Not saying this is your problem, but maybe one of many possibilities.

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Old 05-24-2014, 11:09 AM   #5
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Broken rocker will give you a engine misfire. Possibly a broken flywheel or a rod or main bearing comes to mind. Piece of carbon is a possibility as well. Pull the dust shield of the tranny to inspect the flywheel.
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Old 05-24-2014, 09:32 PM   #6
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ok, i pulled the starter & insp cover & turned ring gear 360. bolts tight & no cracks. looks good. pulled both valve covers, all rockers & valves & pushrods good. this isnt looking good, not much left but bottom end. looks like its crusher bound. crazy, no noise at all before this then stopped at the store for 5 min started it back up with full blown knock.
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Old 05-24-2014, 09:45 PM   #7
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Drop the oil pan and check the connecting rods for play.
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Old 05-24-2014, 09:54 PM   #8
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ya, thats what im thinkin . if its a rod its gone but the pan is easy to get off so i think ill have a look. thanks for the help.
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Old 05-24-2014, 11:53 PM   #9
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Okay, so is the engine running smooth other than the knock? Does it by any chance sound different like maybe a low popping noise from the tailpipe? Another thing that happens on engine shutdown at 60K to 70K with belts or plastic coated gears is they jump timing! On start-up, you might well hear a piston smacking a valve if that happens. Looking at a parts list for those engines, it also shows it has a tensioner assy. If that snapped or was way worn, it may have let it jump. Try the dollar bill on the tailpipe test. Hold a fairly crisp bill up against the tailpipe while it'* idling and it should be blown away in a steady motion. If the tailpipe sucks it back up against the opening and then it blows away from it again really quick, that means it'* sucking air back and that is usually a dead miss OR bent valve. God, I'm showing my age now.

Just a theory based on other situations with other engines that shut down fine and then woke up sounding like someone dumped bolts in the intake or oil pan. Rods and bearings just usually, keyword here being usually, don't go **** up on shutdown.
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Old 05-25-2014, 12:34 AM   #10
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That trick with a dollar bill also could be because of a broken exhaust valve spring....
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