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The engine has developed a knock

14K views 90 replies 12 participants last post by  darkman 
#1 ·
A little back story, because I like to tell a story. Bought a season pass to the drag strip, opening day is today. Fire the beast up this afternoon and I hear a slight knock, most people wouldn't hear it. I blow it off. Get to the track and take a breather and gather my bearings because I'm still getting used to 600+hp, hopping on the freeway I gave it in 3rd gear and I got the "traction engaged" message! Not bragging, but more adrenaline rushes when I drive this car than the 150hp (02 suzuki gsxr 750) sport bike I used to know as the only thing to get my adrenaline going. Ten minutes pass and I get in line, I'm two cars to the tree sitting next to a building with my window down, I hear the knock echoing off said building. I ask the traffic director "Is that me" he replies, "yes". I ask how to leave and he tells me to pull out through an opening, and states "don't blow it up"

We first thought rocker, but it may also be a bearing in the charger. It's not a bad knock, but it got worse from the drive there (20 miles) so I know it is something.
I have yet to tear into an engine, so I don't know much about them. I still have 30+ lbs of oil pressure at idle, I don't think it's that big of a deal, but, like I said, I haven't torn into an engine and have no idea what I'm getting into.

I know my description isn't much to go by, here is a video I took earlier today (before I left for the track). You probably won't hear the knock (drivers side is where it sounds like it's coming from) but I'm trying to give as much info as I can.

http://www.youtube.com/watch?v=7k-eyBRWH2c

I plan to get another video when I take the stethoscope to it to hopefully find out where it's coming from. I don't want to fire it up if I don't have too.

What I know about the heads is:
Ported and polished by BES engines
Patriot Gold Dual springs and Ti retainers
Comp cams 7.450 pushrods with Yella Terra rockers

I will ask the previous owner if he can find out more about who did the work (the guy he bought it from had the work done).

For those who want to help me figure this out, but don't know the car:

http://www.cadillacforums.com/forums/2004-2007-cadillac-cts-v-general/284959-i-bought-one.html
 
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#6 · (Edited)
the frequency of it should tell you something--crank- vs cam-centric (not official terms; made up by me just now)

...or ignition-centric.

...the crank turns twice for every revolution of the cam. the pistons and rods are tied to the revolutions of the crank, and everything in the upper half (heads/valves) are tied to the revolutions of the cam.

and if it only happens during a spark/cylinder ignition, that's significant as well. you can isolate that by disconnecting plugs one at a time.

you can also get yourself a cheap listening tool, basically an aluminum rod that will allow you to localize the sound by touching it to different parts of the engine

to get the most accurate indicator of the revolutions of the crank, use a timing tool that flashes a light at every ignition of one of the cylinders. a flashing light is easier to interpret than trying to keep track of the markings on the harmonic balancer with the un-aided eye.

it's pretty easy to tell whether a sound is at the same frequency as the timing light, or twice as frequent (or another rate altogether/irregular)

also check for a smell in the exhaust. oil smells like burned oil, coolant smells like... burned cat urine-ish.

//I just had a listen, that's more of a rattle, sounds rather irregular. how does it change with increased RPMs? (sort of a two-person job, one person to man the camera/mic).



who pulls a tune? the man admitted he's never torn an engine apart. he's here for help. what would you do with a tune, izcain? do you know how to read one? do you know someone who does?

like you wouldn't jump on a V with that motor in it, as long as it sounded fine. I would, no doubt in my mind.

//...wait. is it for sale? (discount for the noise?) :-D I'm such a dick. I'm just teasing, I think it's gonna be OK--I was expecting worse--like, an obvious knock due to blow-by (gouges in the cylinder walls).

truth be told, I don't have any personal experience with valvetrain failures nor have I heard them first-hand, so I am not qualified to say it isn't a pushrod or broken spring, or anything else loose under the valve covers (especially not from here). I've had everything else go wrong with engines of mine, though.

I was at one time long ago, an ASE cert-holding Air Force mechanic.

//izcain is just mad that you have a super ****in' awesome car. I think he's one of those guys who can't just be -happy- for people who have nice things

//so far it's been robojesus and izcain to the rescue. God help you

where are you? Los Angeles area, by any chance? I have... nothing going on Fri-Sun (full-time student now. your mom goes to college!).

oh nevermind. you're way up there. damn... that's you? shit, man, um...

ok, to share exactly what I'm thinking, I am curious exactly how much driving you did on the motor before the sound started. I wonder this because there are things like Lucas oil products that will thicken the oil and hide sounds and symptoms temporarily, say, long enough to sell a car.

I hope that's not the case... that the sale was driven by an imminent problem.

maybe there's just a switch you missed in the cockpit, or you gotta jiggle the handle or something. (just don't jump through the phone at 'im! [especially not on account of what I just said about the Lucas oil])

//I like stories, and humor. I was also a medic, and know that telling and relating to stories is an indicator of a favorable prognosis. having a name like robojesus is not.

//k i'm done. I'm not always like this. it's only when I'm awake. sorry
 
#4 ·
I didn't pull the tune, I was assured numerous times by the seller that it is tuned for safety. I'm set up to have it towed to a speed shop tomorrow. I will most likely have them dyno tune it (after they fix it). I just had my neighbor have a listen and made a small video. The beginning of the video is of the drivers side of the engine and then moves to the passenger side. The noise sounds like it's coming from the drivers side.

http://www.youtube.com/watch?v=***0IYKQGMQ
 
#7 ·
I haven't revved it since the noise started, but it's consistent with idle. I drove it 600 plus miles home, the noise came only 50 or so miles after that. I don't believe the seller tried to screw me, he has numerous thousands into it to make it good in the few months he owned it. The oil was changed hundred or so miles before I Bought it with Mobil one. I was told to change the oil before taking it to a shop, I think I will do this. Any filters and weight recommendations? I'm not even sure how much or if The pan is still a stock ls 6 I'll get under it as soon as I have the chance.
 
#8 · (Edited)
man, I forgot about how loud the exhaust is.

assuming:
-your oil pressure is 30 idle/40ish above-idle,
-you have fluid in the cooling system, and the temps are fine...
-and you don't smell oil or coolant from the exhaust...

try to:
1: isolate the sound with the stethoscope,
2: do this rev test (and get a recording of it):

4k (midrange) and hold,
then 5.5k (high-ish range) and hold.

sounds are more telling as you raise the RPM. as the engine speeds up, the duration of all the actions in the motor are shortened... this causes some things to float, others to bang harder... the timing advances, and oil pressure rises... the balance of rotating parts can improve or worsen (temporarily, through the different RPMs).

depending on the issue, the sound could simply speed up with the motor(in "lockstep"--you'll be able to tell, and it would indicate something linked directly to the crank or cam, and 2:1 crank to cam rotational ratio is key in determining that), but it could also get louder, get softer, or go away (indicating something secondary to the crank or cam, such as lifters, pushrods, rocker arms, springs, valves)

so. a useful sound bite would be bumping the rpm a few times ("stoplight revs"), and holding it at 4k and then 5.5k-ish.

doing it while rolling and accelerating under load might produce different results, as well.

and then there's figuring out where it's coming from--high/low? front/back? left/right... also try unplugging the power to the coils one by one (isolate cylinder spark/ignition)

also try disconnecting and reconnecting the battery to see if doing a "soft" reset of the computer makes the sound go away. (for the MAF and the speed density tune you have, which I'm not familiar with, but it's worth a try to "turn back" an error counter that the computer might have decided it had enough of--though 600 miles is a little long, and if what you say is accurate, the sound has grown louder...)

If you could reduce the sound coming from the exhaust, -somehow- that would help with this endeavor. maybe extension pipes trailing out the back end of the car, and under the garage door... I don't have ideas for that one, other than something like an exhaust extractor (like they use in shops).

It could also be something -really- simple, like loose exhaust flange bolts, or the headers coming loose from the block. aftermarket headers tend to come loose, constantly. exhaust leaks can sound like knocks but they'll also have a "putt putt putt" quality to it. see real quick if the sound is more noticeable under the car, nearer the transmission.

I should invest in a code reader; I would like to hook one up for this. they're inexpensive and they make bluetooth enabled ones that remain plugged into your computer and will send real-time readouts to your smartphone.. sub-$100 range, if I recall correctly. Ebay, and I've seen auto parts stores carry them)

lastly: do you still have full power out of the motor (has there been a noticeable drop in power)
 
#10 ·
D3,
I applaud your efforts to help Matt. I can also understand why you would suggest Lucas oil being used to hide noise. I want to ensure you and Matt that this was not done. Actually, you can tell if Lucas was used by looking at the dipstick and even more so when changing the oil. I would not of spent over 5 grand on the car before selling it if I was trying to hide anything.
To me, it sounds like lifter tic. There are common reasons for this. Deposits in the oil, bad lifter, low oil, or bent push rod. Although the oil had about 1k miles on it when he took it, I suggested he change it out and maybe put a slightly heavier weight in it just to ensure any deposits were not the issue. From there, taking off the valve covers to see where it is coming from is next.

----------

I just read your comment about a loose header. That is a possibility also that I did not take into account. A long time ago, I drove one of my dad's hot rod's. I down shifted at a high RPM so they exhaust would pop. One too many times and it back-fired pretty loud. A similar noise, as a lifter would make, came afterwards. It ended up being a blown header gasket.
 
#11 ·
D3, you crack me up. :thumbsup:

Actually, I had a header leak that may have sounded like this, but mine was more subtle, and my hearing wouldn't allow me to hear it though EVERYBODY else said they could. Had new gaskets put on, buttoned up really nice, and now it's quiet. The sound in your video does sound like that kind of leak, only more pronounced than mine. Sure wouldn't want you to undertake that kind of effort (and expense) unless you were pretty certain that's it, though.

Question becomes how best to determine if it is a header leak. D3's "stethoscope" recommendation is probably the way to go. Even a portion of a doggone garden hose with one end at your ear and the other end moved around and positioned down near the exhaust ports might work. You just need to focus such a listening device at the location of the noise and get it to your ear to determine exactly where it's loudest then better problem identification can occur.

My $0.02.
 
#12 ·
I know the stethoscope method is widely recommended but on a recent issue w an ls1 this proved to be ineffective for me. You could hear the tick everywhere. It turned out there was a bent pushrod, bad lifter, and damaged cam lobe. There really is no replacement for opening the engine and investigating.

The garden hose should help to find exhaust leaks but if you have an aluminum block the stethoscope may not help localize the issue. Pulling the valve covers and checking for a bent pushrod and loose or failing rocker is pretty easy. Going further will likely require pulling the heads.
 
#13 · (Edited)
:-D

I did not mean to offend! the thought crossed my mind "what if" the previous owner is on the forums, but I did not consider it would be an apache pilot (gimme a break! lol are you WO or O-type?)

umm funny story about Rucker... anyway.

I feel like I should have asked:
-does it have solid lifters, or rollers, or hydraulic rollers...?
-did you gain altitude between the sale location and your home, by any chance. I have never messed with timing on OBDII engines, but... what's that about advance--maybe you need more octane...... (what does the +1 advance mean/how was that accomplished, I wonder)

what octane does it use? was there an explanation for the 8:1 compression and low boost? just curious

there is a huge chance I am wrong about everything I say, but if I'm wrong, might as well be wrong strong
 
#15 · (Edited)
the whole thing? I did not see that coming.

//the more I think about it, the more the MAF delete bugs me. Try... an octane booster additive, one of those $5 bottles from Wal Mart or a parts store. Couple bottles of it, even

Assuming everything is in the same working order as when you picked it up, the only things that changed are the car's location (altitude, temp, humidity) and the fuel (octane)...
 
#16 ·
what is "so far it's been robojesus" and "god help you" supposed to mean? i don't think you have a clue who you're talking to kid. news flash my dude, i'm not someone who puts 8 inch kickers in the footrests of the rear seating area.

when you've built a few engines, and done work on your car other than changing fluids, you can talk to me like i'm retarded. you're no expert. i wouldn't trust your ass changing my oil.
 
#18 ·
HA! Success! Funny you mention the subs, this was 100% about your previous subs comment :)

And I know exactly who I'm talking to! Youre robojesus!

WIN. Made my day

//I misspoke earlier. A timing light will flash with each revolution of the cam, not the crank.

C'mon guys, don't be like that--OP shouldn't suffer for my behavior--if you have something to suggest, say it!
 
#29 ·
Exactly which previous subs post are you referring to " some of ago"? I think you have the wrong guy pal

.

----------

I haven't read the codes, I trusted the previous owner on this. He said there is a way to turn it off, I just haven't messed with the efi live yet.
I agree. That would be one of the first things done with a speed density tune imo. It was either overlooked, or the tuner isn't worth a shit and probably broke the motor with his neglectful tuning.
 
#19 ·
Alright, back to trying to help this dude fix his issue.

deltaecho said that the headers back off of the block. They DO NOT back out of the block... they can unbolt from the head due to engine vibrations. Spray carb cleaner around the headers where they meet the head. If there is bubbling, then you will know you have an exhaust leak, not a surefire way, but it's a viable way. This is best case scenario, but highly unlikely.

second, you need to pull the valve covers. unbolt your rocker arms and remove the entire pedestal. you can tap on each lifter with a pushrod LIGHTLY with a mallet or hammer, if it goes down pretty easily, you have a lifter that is collapsing and is reinflated over time. That being said, if it's collapsed bad enough, the pushrod will be noticeably deeper down than the other 15 pushrods.

third, drain your oil. check for abnormal metal shavings. take your filter out, slowly cut it and strain it through a paper towel into a basin... then again, closely examine for excess metal shavings.

When I spun my rod bearing(s), I was unable to maintain good oil pressure, and the car had very little power, especially up top. This is rod knock in an LS6... I do not think this is what your car has.

Forward to 0:37 in this video. This is what my cars valve train sounds like all the time, due to a massive cam and noisy ass dual valve springs. With the higher open seat pressure of the springs, the valve snap back to closed a LOT harder than what you're used to hearing. A quick google search of "dual valvesprings noisy" brought this thread. In my estimation, I would not be surprised if you had:

1. Collapsed lifter.
2. Bent/Damaged Pushrod
3. Exhaust leak.

I do not think you have:

1. Spun rod bearing
2. Spun/damaged cam bearing.
3. Bad main bearing.

If you could get me a higher quality sound clip, I could make further guesses.
 
#20 ·
oh, yeah. right... headers bolt to the heads (you sure?)

umm... the troubleshooter in me would like to know the location of the noise in relation to cylinder, and which cylinder's ignition it coincides with. you could narrow it down to a single set of lifter, pushrod, rocker, spring, and valve (based on the four cycles of intake, compression, ignition, exhaust compared to which cylinder's ignition spark corresponds to the noise). ideally.

an example of a useful finding: "the noise happens when cylinder 4 fires, but it's right above cylinder 1"

that's if the noise occurred cleanly, but that rattle sounded fast, like once per cylinder.

I've rebuilt one or two engines a year since 2003, of my own but usually someone else's to lend a hand. I'm not familiar with our motors and I tackle issues as they happen.

I'm rusty.
 
#21 ·
Please tell me you're not on a car forum suggesting that I'm incorrect in stating that headers connect to a cylinder head, rather than a block, all while insulting me?



see the pairs of valves here in a 243 casting head? INTAKE AND EXHAUST MAKE A PAIR.

See the fancy orange stuff covering the strange shaped holes? Those would be the exhaust exits.

Your easiest bet is popping a valve cover and taking a look around, not sure why you're suggesting he use octane booster LMFAO.

And pertaining to the "rusty" comment, I'm afraid you're just not as smart as you think you are. The LS1 based engines are EASY and basic as hell to figure out.

And why does the MAF delete both you? Have you never heard of a speed density tune?


OP, I glanced at another video of yours, and I need to know why the CEL is illuminated in this video:

http://www.youtube.com/watch?v=m9MBFy__V2M


and listen to this video:

http://www.youtube.com/watch?v=fJCjjhcaTEM it's a dodge with a header leak.
 
G
#22 ·
D3 - You were going strong with the frequency of the noise but lost all credibility with what seems like drunken babbling then suggesting an octane booster.

carsaremytoys - Check the headers for a leak then remove the valve covers and take a close look at everything. You can also run the motor at idle with them removed without oil squirting all over. It's also real easy to pull the rocker arms and pushrods so you can see the individual cam lobes.
 
#23 · (Edited)
naw, i mean if it's a rattle more than a solid once-per-cycle sound, I'm thinking it could just be an altitude difference the engine can't handle as well as if it still had the MAF. and no, i'm not familiar with a tune that doesn't use a MAF to (I dunno) accurately measure how much O2 is entering the engine....

this is not a normal motor we're talking about, and we have ignored the CEL.

Vegas is 300 miles from me, and it's an altitude change of 2200 feet. OP drove 600 miles from where he purchased it? OP if you dropped significant altitude, it's effectively increasing the compression in your cylinders. 8:1 and 5.5lbs sounds weird-low, I wonder if it's that way because it's compression-sensitive (OR SOMETHING)

or the 8:1 compression ratio is inaccurate and it's actually higher

robojesus, I was kidding, yes you're right... man i was just playin' about asking are you sure...

look i'm sorry, I more than got you back for the sub comment in that thread some weeks ago

wow, I got you good, I even made you pull a head to prove a point!

//I would quit the internet forever if it turns out to be an octane/altitude issue(and I'm right). i promise
 
G
#25 ·
If the MAF has been tuned out, the cel should be turned off in the programming also. It's very simple to do and doesn't make sense why the code would not be disabled. Have you read the fault codes with a scanner lately?
 
#32 ·
Sorry haven't got back to this. been pretty busy. To answer a few comments. The MAF delete is because of the SD tune. The CEL was not on when I bought the car. I had the clutch replaced and when they hooked the battery back up, it was there. It was scanned and found out to be the MAF. I picked up the car and was told it need to be re-flashed with the tune to have it Permanently turned off. I do not have the knowledge to do that nor the balls to reflash it without thinking I would mess it up. The more I here it and think about it, I think the header gaskets may be leaking. Hope this helps. I will butt out of this conversation so others don't think I am trying to make excuses.

OP, give me a call if you need anything from me.
 
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