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Discussion Starter · #1 ·
Okay, so like the title states, my engine has developed a knock. But first here's a little background on the engine:

a few weeks ago i let my dad borrow my 95 firebird (lt1 150xxx miles) since he was having vehicle issues himself, and it was running in fine condition at this point. when i got it back, it ran like garbage. it had an awful sounding knock and it felt like it wasnt running on all 8 cylinders, so i instantly thought "oh great...another head gasket blown" (i have had bad luck with head gaskets in previous cars) so i just drove the car about two blocks to get home and parked it. next day i went out to get an idea what was wrong with it and started it up and the knock mysteriously went away but it was still running like crap. so i read a TON of threads on here and alot of my symptoms matched that of a bad opti, so i went and replace the whole opti, plugs, wires, serpentine belt, waterpump, crankshaft seal, thermostat, fresh 10w30 synthetic oil, (was no metal shavings in oil) and thought i was in the clear. started it up, and it ran much better, but that "knock" came back. its strange because it is ONLY at idle or low rpm and kinda smooths out when driving, but if you take your foot off the gas and cruise the car runs rough (slight vibration) and you can hear the knock. same thing when parked, it will knock until you hit the gas and pick up the rpm's and then it smooths out. after reading through a whole ton more threads, only two things have come up that seem similar to my issue, 1: collapsed lifter or some sort of lifter issue,, 2:i have a "dead" cylinder.

so after throwing a decent chunk of money at this issue already, i was hoping someone on here could help me diagnose this before i just start throwing random parts at it and wasting money? i will try to get a video and upload it tomorrow. sorry for the mega long post, and thanks for reading :LS1LT1flag:
 

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Damn knock!!

I had the exact same problem with my 96 SS, but mine came at only 65k on the clock. Like you said, mine ran like dirt after it developed the knock. The knock came from no where, I parked it one night after work, came out and started it the next morning and there it was. I called my step dad who sold me the car, and is also a mechanic, and he promised me nothing was wrong with the car. So I continued to drive it. I could here the knock when starting it up, and low rpms, but when I put my foot down a little it was gone. Beware it doesn't stay that way forever. I took it to a mechanic, he told me a needed a tuneup, even though it had only been 10k since my last one. I decided to get the tuneup, and $500 later sure enough the knock is still there. Nothing was getting worse, so I continued to drive it, and everything was fine for about two months except for the embarrassing knock. I came out and started the car one day for my lunch break and the knock was ridiculous, but no extra loss in power, and no money until payday I decided to drive it until I got my check. WORST DECISION EVER. Each day the knock got worse and worse, but still no noticeable loss in power. Then while driving to work on the highway the car just jerked back and started hopping I pulled over into the shoulder, but before I came to a stop I heard a loud pop, and smoke went everywhere. When I got out of the car I noticed all of my oil from the from the car to about ten feet away. Towed it home and decided to play mechanic which is something I've never done, took off the valve covered and under the passenger side cover I noticed a rocker arm just laying in there not connected to anything, I called my step dad who looked at the car, and I had thrown a rod. I suggest you drive it as little as possible, and have it checked out by a credible mechanic, and get the problem fixed before you wind up like me. I wound up spending over $3,500 for something that probably would've been somewhat of an easy fix. I don't know much about cars I just like to drive, and if you have the same problem I did you won't be driving after long if what happened to me happens to you as well. Sorry for making this so damn long, I hope it was at least a bit helpful.
 

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Discussion Starter · #3 ·
Wow! Thanks for the insight! I'm taking it to my buddies shop tomorrow so we'll see. Did you ever find out what was causing your knock however?
 

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Before you check for the worst, try removing the serpentine drive belt and see if noise goes away.

Of course take 96S's advice and drive car as little as possible, but you might get lucky and find one of your accessories is making the noise. If not, check the valve train for loose rocker arms, bent push rods, broken valve springs.

If no, then jack engine up high enough to pull oil pan. Check your rod bearings first as they are the most likely suspect for your knocking noise. If you find a spun bearing, or one that is completely worn out, you will also need a new crankshaft.

New rod bearings by themselves won't fix the problem. And when you hear bearing knock, the crank 99% of the time is worn so bad it can't be turned down to fix the problem.
 

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Discussion Starter · #5 ·
I really hope it's nothing major :( and it will be driven very little, I live in town and my buddies shop is right around the corner. I'm sure if I baby it it shouldn't get worse.

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Discussion Starter · #6 ·
Also from what I can tell the knock isn't from the bottom, it really sounds like it's somewhere up top

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Discussion Starter · #7 ·
Before you check for the worst, try removing the serpentine drive belt and see if noise goes away.

Of course take 96S's advice and drive car as little as possible, but you might get lucky and find one of your accessories is making the noise. If not, check the valve train for loose rocker arms, bent push rods, broken valve springs.

If no, then jack engine up high enough to pull oil pan. Check your rod bearings first as they are the most likely suspect for your knocking noise. If you find a spun bearing, or one that is completely worn out, you will also need a new crankshaft.

New rod bearings by themselves won't fix the problem. And when you hear bearing knock, the crank 99% of the time is worn so bad it can't be turned down to fix the problem.

well i wont be able to get around to tearing anything apart until atleast tomorrow, but in the meantime heres a short video, sorry for the terrible quality it was a cell phone video :(

LT1 knock? - YouTube
 

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coco is right, check all the stupid easy stuff first. i dont' have sound at work so i cant view your video, but..

start with the accessory drive, and pull your AIR pump relay if the air pump still exists,

hold a long screwdriver to your ear, run it, and hold it against the valve covers.

dont have to tear anything apart to do the initial checks. de-belting the lt1 takes 10 seconds. trying to isolate the noise takes 10 seconds.

check for big exhaust leaks yet? get 'er hot, pull a vac line (the egr one is convenient) and throw a few drops of ATF in there, have a buddy hold some rags over the tailpipes so you get some extra backpressure. see any smoke billowing out of your manifolds?

i swear to god every time i think i've thrown a rod, i've opened my hood and found an exhaust stud has rusted off or something.
 

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Discussion Starter · #9 ·
Thanks for the info guys! Ill be sure to try this. I didn't notice any exhaust leaks and its all stock nothing deleted.

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the thing about rod knock, if you have it, is many times it sounds like it's coming from the upper engine parts, when it really is coming from below.

One way to diagnose rod knock is to run engine with one spark plug disconnected at a time. If you do have rod knock, when you unplug the spark plug from the affected cylinder, the noise will get much quieter. I forget which cylinder it is but sbc's and lt1's have a favorite rod that fails first and causes the knock.

I'm sure another member who remembers which cylinder it is, will chime in.
 

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ha thats funny i just got my car going last sunday and same thing, i changed oil and didnt help, so please keep us updated on what you find out, im trying to decide if i want to try these things or drink my sorrows away?:craz28:
 

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My step dad said the heads were worked on for better performance, and that after about 10,000 miles I should've re-torqued everything, and since I didn't have that done it caused me to throw a rod. At least that's what I got from his explanation.
 

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So I think it was just a loose rocker arm at first, and then it turned into a major problem. It doesn't take very long to check, all you have to do is take off the intake and the valve covers. It only took me about an hour to take everything off and put it back on.
 

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I just watched the video, I didn't see the link first time around. Your knock sounds exactly the same as mine, and like you said, mine didn't sound like it was on the bottom either, it was definitely up top.
 

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My step dad said the heads were worked on for better performance, and that after about 10,000 miles I should've re-torqued everything, and since I didn't have that done it caused me to throw a rod. At least that's what I got from his explanation.
i can't think of any situation where a couple of loose head bolts would cause damage to a connecting rod... unless it pissed so much pressurized coolant into a cylinder that it hydrolocked. and you'd feel that one.
 

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Sounds like your step dad may be a lil shady. At any rate follow all the advice hear. If you continue to drive it just pour in some thick oil. If I were you I would find out how your step dad used the car and what all he has done to it from A-Z. Or he should buy it back..just saying. At any rate a good solid rebuild may be in your future. Have you searched your possibilities yet?
 

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Your step dad ripped you off, he sold you a clunker...

Yeah check your valve train, pull the covers and check your rockers, rocker preload, pushrod straightness, and your valvesprings. Also let it idle with the covers off, look for any weird movement.
 

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Discussion Starter · #19 ·
I just watched the video, I didn't see the link first time around. Your knock sounds exactly the same as mine, and like you said, mine didn't sound like it was on the bottom either, it was definitely up top.
sounds like a loose rocker to me,possibly collapsed or stuck lifter

man, i'm glad to be hearing this! hopefully when i tear into it tomorrow this is what i find, or maybe ill luck out and it'l be something really simple and stupid :D we'll see. thanks for all the responses and input guys, really appreciate it!!
 

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drive it as little as possible

From the sounds of that thing, You could not pay me to drive it. It sounds like a broken pushrod or something that could be catastrophic. Don't drive it. Drive it straight to the shop, tear off the valve cover, inspect, it sounds like it's coming from the drivers head, i'd start there. Good luck man, keep us posted.
 
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