Loud engine knocking noise 3.8 (6g75)

[OutOfTowner]

Hi guys, finally just bought my first 4x4 3 months ago and now my engine has a loud knocking noise from what sounds like the top end. Sounds like a valve and piston are hitting together. The engine is a 2004 3.8 petrol (6g75)

Without opening it up I can only speculate what the problem is so I have a couple of questions.

(1) are the rocker arms designed to break on these engines before causing valve damage like the diesels?

(2) do these engines have a balance shaft?

(3) Initially after reading a few posts about broken rockers I thought it may be the case but after thinking it through I thought if I broke a rocker, wouldn't the valve spring return the valve making it impossible for valve piston contact?

[Pauly Faulkner]

The valves will break before the rocker arm does.
There is no balance shaft.
If a valave wasn't opening you would feel it power wise straight away.
if one of the valves hit the piston it would bend straight away and you would also notice that power wise as all valves on that cam would likely hit as well, not just one.

Lifters and hyd timing belt tensioner are the first things that come to mind.
try and narrow the source down with a bit of hose to your ear.

[OutOfTowner]

Thanks for the quick reply I love this forum already

I'm not sure if there is a loss of power as it happened whilst driving into my driveway and the noise is so loud and nasty sounding I dare not drive it. About 50km before this I noticed it was chugging a little, maybe a slight loss of power but not exactly sure as i was sitting in the passenger seat and driver cant remember but it sounded like something was flapping / flying around under the bonnet. The noise and chugging disappeared after a couple of minutes so didn't think to much about it at the time.

Anythings possible but the timing belt and tensioner were replaced around 25,000 km ago but won't rule that out just yet.

I suppose the only thing I can do to see if its the lifters is to pull it down right?

[OutOfTowner]

Hi guys Thought id post a clip I uploaded to youtube as I still haven't got on top of my engine knock. I tried using a hose to narrow the possibilities but got nowhere. I made this video on my iPhone so the noise is actually much louder in real life. I'd really appreciate any ideas. I'm leaning towards Pauly's hadnt listened to yet theory of lifters. http://youtu.be/GSPoUlzbkUM

[Gen3]

sounds like a stuck lifter to me , any evidence of lack of oil changes ?

[OutOfTowner]

Good point gen3 I only recently brought it and it had just had a service as I was given the receipt but who knows prior to that. Thanks for the reply

[OutOfTowner]

Feeling pretty confident this knocking noise http://youtu.be/GSPoUlzbkUM is a stuck lifter. Should I try an engine flush additive and run the engine or could doing so cause damage

[Goodsy]

Ok stupid question. Have you checked the oil? You mention it just had a service.

[Pauly Faulkner]

Sounds like stuck lifter to me too.
Verify oil level first as Goodsy mentioned.
You can try an engine oil flush but I'm not convinced it will work, nothing to lose other then a few bucks on oil and flush additive. With the additive it needs a good 15mins idle when hot minimum to get to where it needs to be.
Chances are the rocker covers need to come off and the lifter physically cleaned...or just replaced. With covers off you'd be able to check for loose rocker arm to find the stuck lifter.

[OutOfTowner]

Problem solved

Not a stupid question Goodsy...as it was the first thing I checked. I also did an oil change thinking it may help but there was no change.

Pauly, I too was very skeptical about an engine flush doing the trick but as you said "what have I got to loose" I added Liqui Moly engine detox to the oil. After about 2 minutes it started to run rough and then like magic, the stuck lifter freed up and the knocking noise disappeared. I let it idle for a further 20 minutes Engine is running smother than ever. $24 from supercheap auto and worth it's weight in gold ! I'm one happy man.

[Betz]

What a great result!

[OutOfTowner]

Cheers Betz, now I can concentrate on a few mods

[crimespree]

Not a stupid question Goodsy...as it was the first thing I checked. I also did an oil change thinking it may help but there was no change.

Pauly, I too was very skeptical about an engine flush doing the trick but as you said "what have I got to loose" I added Liqui Moly engine detox to the oil. After about 2 minutes it started to run rough and then like magic, the stuck lifter freed up and the knocking noise disappeared. I let it idle for a further 20 minutes Engine is running smother than ever. $24 from supercheap auto and worth it's weight in gold ! I'm one happy man.

Thanks for this, just had the EXACT issue for mine and resolved it in the EXACT same way, Cheers.

[Bama_Kiwi]

Problem solved

Not a stupid question Goodsy...as it was the first thing I checked. I also did an oil change thinking it may help but there was no change.

Pauly, I too was very skeptical about an engine flush doing the trick but as you said "what have I got to loose" I added Liqui Moly engine detox to the oil. After about 2 minutes it started to run rough and then like magic, the stuck lifter freed up and the knocking noise disappeared. I let it idle for a further 20 minutes Engine is running smother than ever. $24 from supercheap auto and worth it's weight in gold ! I'm one happy man.

Thank you for this update. Making a mental note for the day it happens to me.

To clarify, do you then need to subsequently change the oil after the Liqui-Molly has done its job, or do you just carry on per normal?