[eagleprime]

I recently started hearing a knocking noise coming from my engine. It seems to be the same knocking sound that a lot of other people on this forum have been wondering about, but never seem to report back on what the issue was.

TL;DR: there's a disconcerting knock coming from approximately the middle of the engine, initially only at low revs, but is now also audible at idle. Video of someone with that same sound:

Full story: I bought an '03 GT V6 Tiburon with 180k miles/294k km on the odo for 2500€ this February. When I got it, it seemed to be running fine, except for a belt squeal, electrical issues and various leaking gaskets, primarily valve covers.

I fixed the belt noise by installing a new Gates serp kit. Car seemed to run fine. I then parked it for about three months while I fixed various issues, including the valve cover gaskets, and installed new spark plugs and leads. When I initially got the car back together (still on the old oil), it seemed to run fine. However, when I started it up the next day and let it warm up, I started noticing a faint knocking noise at mild revs. I drove it for a bit, initially slowly and then using more of the rev range, the noise was not detectable above 2500 rpm or under 1500 rpm.
Thinking it could be a lazy lifter, I changed the oil (looked brown, not black) and added some LiquiMoly Hydraulic Lifter additive to the Valvoline 10W-40 I filled it with. I used an OEM Hyundai filter, the old one was by MannFilter. During this operation I found aluminum glitter/paste in the little groove of the oil cap hole (but none deeper in), and there was faint evidence of metal in the oil, too - the pan I drained the oil into wasn't clean to begin with, so I unfortunately can't be sure of how much metal there actually was. No evidence of glitter in the filter hole, but I've not yet autopsied it. I'll update the post once I get around to that.
After the oil change I took it for a spin, both slow and fast, hoping the situation would change. Indeed it did: the knocking is now detectable at idle.
Engine has no trouble revving, there's no new shaking or instability, just what I think is a harmonic vibration at about 2000 rpm.

To locate the source of the noise, I used a prybar as a stethoscope. I checked both valve covers, power steering pump, exhaust header, serp tensioner, alternator and AC compressor - all steady sounds. The noise was detectable but faint when the bar was against the engine block. The sound could be heard the best with the bar against the thermostat housing. With the naked ear, the sound seems to be coming from the timing belt area.

Speculation:

• Could it have knocked before I got it? Perhaps, but I can't remember such a noise.
• Could I have gotten a piece of gasket silicone into an oil passage bad enough to starve a bearing of oil? Perhaps, but the same noise has been reported by others for the last 14 years, and in only one case valve cover work was involved.
• Could it be a spun crank bearing? Perhaps, but I'd have expected the engine to have seized or at least gotten noisy as hell at high RPM by now.
• Maybe I have too much oil in the engine and the crank is splashing into it a little? The dipstick got hard to read, though I think I was just slightly past the full dot, so.. if I'm off on the measurement, there is a chance I'm off on the oil contents, but at worst I'm 3 dl (about a third of a quart) over.

Looking around for others with the same issue, I found this video with the exact same noise as I'm experiencing:

It's that same sort of soft RPM related knocking that goes away completely at revs.

I'm going to try replacing the timing belt, pulleys, tensioner, mounts and installing the Valeo solid flywheel kit simply because I have the parts, to see if I find something or if the noise goes away, as a lot of suggestions have pointed to loose timing belt tensioner or DMF... But I'm also prepared to accept the fact that I spun some bearing or damaged the oil pump, so in the worst case I'll drive it around town until it breaks properly, after which I'll be storing the car until I get around to either rebuilding the engine or buying a new one.

And I'm quite determined to figure out what's causing this noise, so I'll be updating this post and thread as I gather data. I'll be able to go inspect the filter tomorrow evening.


If anyone knows something about this issue, I'd appreciate any and all insight.

 

[eagleprime]

Short update: I could not find anything out of the ordinary when I dissected the oil filter. This gives me some hope that the problem could be alleviated by installing fresh timing belt components. I'll also be building a catback, as the old one is quite rusty and may be leaking, just to see if something changes.
After that, new clutch. If the knocking gets worse, I'll just have to bite the bullet and pull the engine...

Again, any help or insight would be much appreciated. Right now, I'm kind of throwing parts at the issue. Parts that I was always going to install and bought a while back, but.. eh.

Edit: I think I might want to drop the oil once more and check the oil pan and pickup tube, but I'm going to need a fresh oil pan gasket for that

 

[03tibgts]

Why 10w-40 though?

 

[chase206]

Why 10w-40 though?

This right here is the question I have. You should be using 5W-30 synthetic year round. In hotter climates a thicker oil could be used in the summer time but even that's not necessary.

If the car sits for too long all the oil drains out of the head and your hydraulic lash adjusters "deflate" so it's recommended to start it up once a week at the minimum even if it can't be driven. To build up pressure in the HLA's you need to drive it down the road and put a light load on the motor. It will idle all day like that and the HLAs will chatter until you put a load on it and build oil pressure. But I'm willing to bet your oil choice is a factor especially if you are in a colder Scandinavian climate.

There are some conditions where the timing chains between the cams stretch and make contact with the "guides" causing glitter to appear in the oil pan and oil filter. It makes a "clattery" sound if that makes sense. The guides are steel IIRC so the glitter from that should be magnetic. Did you do the magnet test with your glitter? One other thing to check is your thrust tolerances when you pull the transmission for your clutch job. I'm willing to bet with your mileage that your thrust is out of spec and the engine may be eating the thrust bearings which would produce glitter as well.

 

[eagleprime]

Why 10w-40 though?

This right here is the question I have. You should be using 5W-30 synthetic year round. In hotter climates a thicker oil could be used in the summer time but even that's not necessary.

I have no idea what was in the engine to begin with - this was the first oil change I performed on it, but given that it's a high mileage engine, I wanted to see what difference (if any) the thicker oil would make. It did quiet down the engine a bit, from a slight constant rattle to more like a hum - the thicker oil should be taking up some of the looseness caused by normal wear. Also: the knock was there BEFORE I dropped the thicker oil in. To my knowledge, the last oil change was performed at a dealership service center.
The car is kept in a heated garage and will not be driven during the winter, except for a trip to the local MOT inspection center. If that changes, I'll of course drop lighter oil in - for $30 a bottle, it's not exactly financially ruining.

If the car sits for too long all the oil drains out of the head and your hydraulic lash adjusters "deflate" so it's recommended to start it up once a week at the minimum even if it can't be driven. To build up pressure in the HLA's you need to drive it down the road and put a light load on the motor. It will idle all day like that and the HLAs will chatter until you put a load on it and build oil pressure. But I'm willing to bet your oil choice is a factor especially if you are in a colder Scandinavian climate.

The weird knock is not audible through the valve covers or side of the head, which it logically should be if a lifter was stuck. I.e. the knock is there, but it's unlikely to be a lifter. Besides which, the knock got audible at idle after I drove the car and stopped outside the garage, without turning the engine off. Before I set off, it was audible after the engine had warmed up to operating temp and when light throttle was applied.

There are some conditions where the timing chains between the cams stretch and make contact with the "guides" causing glitter to appear in the oil pan and oil filter. It makes a "clattery" sound if that makes sense. The guides are steel IIRC so the glitter from that should be magnetic. Did you do the magnet test with your glitter?

I didn't have the wherewithal to check the glitter that had collected in the oil cap area and accidentally got rid of the evidence by wiping it off with my finger when I first discovered it. I'm kind of new to all this, the Tiburon is my first proper project car, I haven't quite developed all the right instincts and reflexes yet. As for the stuff in the oil I drained out, I did get a very light coating of glittery gunk on my neodymium magnet. The glitter was enough to make me concerned, so I dissected the oil filter, but couldn't find anything metallic there - just some pieces of non-metallic carbon deposits and a few small flakes of silicone sealant that dropped in as part of the valve cover gasket job.
Given that I did find the deposit in the valve cover, at the oil cap, I'm inclined to believe that that particular metallic material came from the head, and it may very well have been from chain grind. I'll check the guides the next time I have the valve cover off (though a proper inspection is going to involve cam removal, and I'd rather not do that on a hunch).

Edit: I should also add that I didn't detect any slapping, clattering or grinding sound when the engine got started up - but I do have a pod filter in place of the airbox, and the engine is very noisy while it's warming up, making metallic sucking noises. It's done this since the beginning, and I've seen it on videos, so I assume this is quite normal.

I'll take some videos when I get back to the garage again - it's not located where I live, I have to travel there by car when I'm off work.

One other thing to check is your thrust tolerances when you pull the transmission for your clutch job. I'm willing to bet with your mileage that your thrust is out of spec and the engine may be eating the thrust bearings which would produce glitter as well.

Good call on the thrust tolerance check, I'll do that when I get to the tranny out. I can probably also try giving the crank a bit of a wiggle while I'm doing the timing components.

Sorry for the novel, and thank you for the reply

 

[WessGM]

Hope that knock sound is just oil related. Update us when you figured it out.

 

[eagleprime]

Hope that knock sound is just oil related. Update us when you figured it out.

I've been struggling with work and personal issues, but I've been meaning to get back to the garage to remove the lower oil pan to check the pickup for debris. Good thing to do in any case.
Personally, I'd be more inclined to believe that the noise is coming from a worn timing belt tensioner or water pump bearing - but we'll have to see about that once I get to it.
Life has a nasty habit of slowing down the progress on hobby car projects.

I'll be sure to update this topic once I know more.

 

[eagleprime]

OK, update / new development.

The oil told me nothing. What I dropped out of the engine had only been used for a ~100 km one night's test drive, after which the knocking got worse. The oil was dark in color, but contained no large particulate, glitter or anything. This suggests to me that the knock is unlikely to be caused by a failed bearing, because since the knock worsened, I should have found more metal in the oil as a bearing would have disintegrated due to the tight tolerances required to keep them working.

The engine knocked pretty bad when I got the engine sealed up again and fired her up with fresh oil. Here's a video of the noise after the engine had settled...

Tiburon V6 engine knock, cold start after fresh oil

youtube.com

Once I took that video I figured I'd take the car for a test run to see what would happen (I was mentally prepared to have the engine fail) - but first I needed to refuel. On a whim (thinking 'it couldn't hurt'), I grabbed a bottle of injector cleaner I had lying around and headed for a gas station and filled her up with the STP and about 40 liters of 'premium' gas (98E5). Not 5 minutes after leaving the gas station I could no longer detect the knock while the car was warm. I found this rather odd

Today I went for another test drive. Here's a video I took of the engine running after it had time to settle after a cold start - it didn't sound rattly at all when it was warming up, but then settled into a somewhat less harsh knock.

Tiburon V6 engine knock, cold start, next day

Added STP injector cleaner the previous night while refueling, and the knock went away during that night. I expected the engine to knock the next day, as wel...

youtube.com

As I headed off for the test drive, I couldn't really notice any knock from inside the cabin. I drove around town a bit, putting maybe 30 km on the engine. As I got back to the garage, I took another video..

Tiburon V6 engine knock after driving around a bit

This is the same engine on the same day as https://youtube.com/shorts/jn5iYtNXL2w - only it's been driven for a while.

youtube.com

Worthy of note: during my test drive, I stopped at a store. When I fired up the engine in the parking lot, I got a good whiff of gasoline that persisted for a good while.

So: what have I learned here?

• This is not a spun bearing - there would be a piston rod poking out through the side at this point if I'd spun a crank or rod bearing. I'm also now skeptical of it being even a slightly worn bearing: because the engine isn't shaking violently at idle and runs very smooth when some RPM is added, it is unlikely to be caused by slop in the rotating assembly.
• Because injector cleaner helped, my suspicion turns to fuel delivery. Given the smell of gasoline as well as a tendency for the exhaust to give a meaty burp when the throttle is blipped, I'm starting to suspect a worn injector.

Besides the smell, there is no external indication of a fuel leak.

I can try to confirm a rich running condition once I get the FTDI cable I ordered so that I can try to gain access to O2 sensor data through the ECU, using the HiScan emulator available here on the forum.
Before you ask: no, MIL ('check engine' / 'money light') is not lit.

Since I'm going off mostly on guesswork here at least until I get the cable or until the engine grenades itself, I'd appreciate any further input you guys might be able to provide. For now, I'll keep driving the car and seeing if something changes.

Oh, and thanks for putting up with me, I know I have a tendency to ramble.



Edit: finding injectors is a PITA - the local stealership quoted me at 180€ per injector and told me that they'd need to be ordered from the manufacturer and the delivery time is "likely several months". eBay offered a bunch of super sketch Chinese knock-offs, so I took a hard pass on that. At this point I'm at a loss at what to do about the engine other than "hope it fixes itself", so I decided to fire the cheapest parts cannon load I could: I wound up ordering a set of injectors (along with clips and a pressure regulator and some other assorted parts) from SpareKorea, which is suspiciously cheap, but that has previously delivered me several less-essential Hyundai branded parts that look to be old OEM stock or very high quality fakes - for the stuff I've gotten previously I'm quite fine with either. However, I'll be taking the injectors to a local shop to be tested before I install them, to be safe, so that I don't inadvertently lean out the engine and fry the rings.
Best case: the injectors are just old stock parts, at worst requiring new O-rings.
Worst case 1: they're fake and I'm out a couple hundred €.
Worst case 2: they're real, but the knocking is due to something different and the engine self-destructs.

Edit 2: I'll see about changing the timing belt, pulleys, tensioner and water pump just in case, when I have the time. Just something I'm gonna need to schedule an entire day and a buddy for.

 

[eagleprime]

Had a nice ride until I started smelling gasoline. Engine seems to run fine now but there's a minor gasoline leak somewhere; car is parked in garage until the faulty part can be identified, my head can't take more fumes tonight so I'll have to resume this later on in the week. Smell seemed strongest on the driver's side (left hand side) of the engine, between the intake and the battery.
So, the good news is that the engine isn't knocking for now... but there's definitely something funny going on with the fuel

I'm just really happy that it's not a busted bearing. Trying to fix a fuel leak sucks a whole lot less than a full rebuild.

 

[chase206]

Great to hear! I was concerned it was an internal problem to be honest. Fuel may have been old and as it ages it loses its octane rating a little bit and causes ignition knock or pre-ignition. We have a stout compression at 10:1 so I would imagine old fuel may pre-ignite.

If you are smelling fuel and it's on the driver's side of the engine bay you may have a bad soft line between the bank2 fuel rail and the hard line mounted to the firewall. If that's not leaking then you may have raw fuel coming up the other line in the EVAP system. The EVAP purge valve under the throttle body can end up with a charcoal pellet stuck in it and it will stay open allowing raw fuel to pour into the throttle body when the tank is mostly full or you take a hard right hand turn.

 

[eagleprime]

Okay, long time no update - the car's been stowed in the garage for most of the winter, we fiddled with the oil a bit, and discovered that adding a thickening agent made the knock worse*. Running the engine in the garage with the car stationary occasionally made the knock go away. Since then the car's not been run, while we've concentrated on fixing other issues, mostly related to rust and such.

On the research side, the sound I was hearing sounded like piston slap, but that was ruled out as "improbable" with a borescope, as the cylinder walls all seemed fine (apart from normal wear and tear on a 180k mile engine). Another video I found described the exact sound and symptoms, and found the source to be the hydraulic timing belt tensioner. The timing belt job is still waiting to be done, but now I'm hoping both that the actual source of the noise is a bad tensioner and that the engine has not skipped time. At least the borescope did not show any valve impact marks on the pistons, which had an appreciable coating of carbon on them.

While draining the oil in order to check and clean the oil pickup tube, we found minor glitter in the oil and pulled the sump, only to find large pieces of plastic in there. Since there's almost no plastic in the entire assembly, we went looking for the source of that, and we found it in the heads - both cam chain guides had been obliterated, neither of them had the rubbery plastic coating they should have had on them, and the one on the rear head had deep grooves cut into it by the chain. I'm at least relieved to have discovered the likely source of the metal, and that it wasn't from crank bearings.
New guides have been installed, and new chains have been purchased, but not yet installed as the thinking last time we were fiddling with the engine was that the chain swap was a lot of effort for questionable gains - though I'm thinking I might as well go through that bit of extra effort, just to make sure the engine does run in exact time once installed, just in case the chains have worn over time or have taken damage from grinding against the metal in the guides, but that requires removing the cam sprockets, which requires removal of the timing belt, which is still pending.

While I was at it, I did replace the evap solenoid, fuel pressure regulator and injectors, as the FPR was showing signs of a minor leak and the evap solenoid was ticking in time with spark (and was old enough to be due for a replacement anyway).

I wish I'd be able to offer a more definitive update on this, or news of success, but there's a lot to do on the car, I'm quite new at all this mechanic stuff, and Real Life with jobs and relationships and everything needs to happen in between.

Oh, since my last update I did get new freer flowing exhaust bits installed (resonator, pipe, sport mufflers), and aside from the engine ticking/knocking noise, the car did sound quite awesome.

Here's to hoping she'll live to see another ride...

*) The working theory behind the thicker oil making the knocking worse is that as the oil pressure increases, the valve lifters cause more drag on the camshafts, causing both the chain rattle and the possible tensioner looseness to be amplified. Lighter oil causes the lifters to be more compliant, making the noise less problematic.

Edit: typos begone

Edit 2: yeah, the gasoline smell I was getting was coming from a bad piece of fuel hose, that got replaced.