Random Knock
Random Knock i have a 94 lt1 formula m6 with 120,000k. it is a DD. i run premium and dont give it too much hell. I have a random knock that just started occuring after i changed my oil. it is on the right side of the engine. when i first heard it from inside the car i thought it was a rod, but when i got out and listened it sounded like it was on top. i took off the valve cover and let it run and made sure all of the rockers were tight and the push rods and lifters were ok(when i listened to it, it sounded like it was a top end prob.) its not a rythmic tic like a valve or consistent low knock like a rod. it is random and odd sounding, anyone have any ideas? thanks for any input.
oil pressure is good so i know its not a cam bearing. rods, valve springs and rockers seem to be good and tight. it does it a little worse when its coming down from a rev but its not louder its just more. im thinking it might be the dowel that connects the piston to the rod (sorry for lack of terminology) but that is the only thing that i can think of b/c it just doesnt sound anything like a main. thanks
Launching!
Joined: Sep 2007
Posts: 245
Likes: 1
From: Clover, South Carolina
Take a long screwdriver, put the handle to your ear, and cup your hand around it to isolate outside noise. Put the head end on your valve covers and intake manifold. Which position is the noise louder in?
thanks for the screwdriver tip thing. im a tech apprentice so i have a good understanding of what it is and could be. that was the first thing i did adn i realized it was coming from the right bank under the valve cover so i took that cover off, put oil slingers on and run it and made sure all of the rockers are tight and everything is working right on top and it is. its not a valve b/c its not a tick + its not rythmic. its not deep enough to be a rod at all. so my conclusion is that it is a wrist pin. im guessing that either the piston or the rod is wore enough to create slop and when firing its making that piston slap around. next thing im gonna do is pull the front 2 plugs ( one at a time) and run it and whenever i dont here the knock, ill hopefully know what clylinder its coming from. does this seem like a good way to diagnose it anyone? I feel like i am on the right track now and im trying to get more opinions. thanks again.
10 Second Club
Joined: Oct 2007
Posts: 2,630
Likes: 28
Sounds like a good diagnostic. Another thing that you should do first, is disconnect the drive belt. Then start the motor for a few seconds. This will eliminate a potentially bad alternator bearing, power steering pump, air pump, a/c compressor noise, etc..... My friend had an a/c compressor go bad and it sounded EXACTLY like a ticking lifter. It's really hard to pinpoint where the noise is coming from when everything is bolted together so tight. Sound travels EXTREMELY well in a solid. My old LT1 motor that was spent had a bad water pump gear bearing. The part that is pressed into the block by the lifter valley. At low rpms it would rattle around and drive me nuts.
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Thanks for the advice joelster. your diagnostic is good too but all of that has been eliminated now. i know its hard to give advice on a knock when you cant hear it. now im starting to think that it might be a rod but idk.
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