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Knocking sound 2.4 JTD

Ok so the car had a knocking sound, which I suppose has now changed a little, to more of a tap since putting some diesel cleaner in and doing a full oil flush tonight. The knock did used to go away when the car warmed up, or for the most part anyway, which made me think piston slap, but now the tick isn't as loud on cold start as it was when I bought it, but it's more constant, getting louder throughout the rev range and staying persistent when warm. I did do a search, but came up with little specifics tbh, anyone any ideas?
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So out of 37 people who viewed this thread, no one has a single clue what might cause the tapping noise I'm hearing? Seriously? Or am I not liked for owning a 156 or something, lol.

Come on guys, help me please, someone must have a clue what it could be, I mean the usual bottom end bearing issues crossed my mind, but it's more a tapping than a knocking after the oil flush. Piston slap seemed likely at first, but now it doesn't go away when it's warmed up, which suggests something, which prior to the diesel treatment and the engine flush, was being affected by the engine being warm, now isn't. It's crossed my mind that this could be a glow plug that's gone perhaps? Could it just be that one cylinder isn't detonating properly? I need some ideas folks.
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Diesel knocks typically on high throttle low revs situations, worse when cold. Plugs go off soon after starting, my 171k 2.4 rattles when I put it into 2nd gear leaving work and lean on the throttle, it must have 1 or more plug off but thats it, it shuts up after. Plugs not usually needed when up and running about. I am a diesel tech but it's very hard to offer opinions on noises I haven't heard. I also have no experience of JTD's, -despite owning one!
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Yeah I'm an ex diesel mechanic myself, but I can't tell if this is diesel specific or not. Doesn't sound like bottom end to me, it's not a dull enough thud/knock, it's a higher pitched tap, it sounded more like lifters originally tbh, but since putting the engine flush and diesel treatment through I'm not so sure anymore.

Definitely sounds like it's on one cylinder only whatever the problem is, because it's a defined knock that gets specifically faster and slower with the engine, as opposed to a rattle or a multi-thud knock.

I'll get a video of it I think, needs to be heard I agree.
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I'm sure they're not totally bombproof but the engines seem to have a good reputation mechanically, -how many miles, whats the history of oil changes etc? I wouldn't expect plugs to make a difference when hot but easy to check if one off, disconnect leads and check individual resistances. Duff ones usually open circuited.
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I only just bought it so not fully clued up on it's history. I know it just had injectors replaced, I know it was serviced reasonably regularly, supposedly it had the oil changed 10,000 miles ago with the cam belt. It's done 156,000 miles, which for a decent TDi should be bugger all really.

I'm wondering tbh, maybe cam belt 1 tooth out? I just can't figure it out, which is weird, normally I'm pretty good at identifying knocks, maybe I just don't wanna admit it's bottom end I dunno, but I just went to listen to a load of bottom end videos on youtube and I don't think it sounds the same. That said, I can't find anything else that does sound like this to match it to, so maybe it is the bottom end?

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Tapping noise made by my Alfa Romeo 156 2.4 JTD - YouTube
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A tooth off on the cam would affect all cylinders equally, a knock sounds like only on one. I did my belt with no special tools, wasn't difficult so you would hope yours was done correctly. Bottom end noises are usually awful on cold start up shutting up when oil gets round then coming back as oil warms and thins, depending on how badly worn shells etc are. I haven't heard of any particular JTD weaknesses.
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Well I'm taking it to see my long standing mechanic of the last ten years, who advised me not to buy an alfa with an engine knock (lol) to see what he says (Other than, you're an idiot). He's been my mechanic for ten years and our families mechanic for twenty, he tends to know his stuff, so hopefully he'll be able to diagnose it. The thing is, I don't think there is any drop in performance (Although I had never driven this particular car without a knock, I had driven my friends 2.4 Sportwagon, which didn't have a knock). I guess will have to wait and see what my mechanic says, if he thinks it's a shell or a bearing, I'll grab some, pull the motor, whack it on my stand and repair it I guess. Just really hoping that isn't the case.
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It's a big heavy lump, it'll take a bit of handling.
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Yeah, so is the VG30DETT I'm building for our 300zx , that's still sat on the garage floor at the moment though, so the stand is free if I need it. I'm still hoping it's not the bottom end, as I really don't want to pull the motor out, but I suppose if it is and I catch it before it lets go, could still be a good engine. That said, it seems I can get a replacement 80,000 mile motor for between £400 - £700, just depends on the prices for the bits I need I guess.
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I have the exact same noise with my engine. Could never pinpoint what was causing it! Thought it was the tensioners or idlers, had them replaced noise still there. Then i thought the exhaust was knocking so i hate CAT removed and the cross member changed as it was blown and still no luck. Now my gearbox or clutch has gone bang so ill see if the noise goes once it has been replaced. If all else fails then ill just leave it cause Ive almost run out of things to change. This is my 2nd engine after the sump cracked on the original one which was as a quite as mouse apart from the usual diesel noise and now this engine has been like that since being put in. That was over a year ago so I know its not the big end thats gone. Let me know how it goes for you... Im thinking it could be injectors, Ive got 2 glow plugs not working but Its a pig of a job to replace so **** it for now
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Doesn't sound dieselly or plug related as the noise seems to still be there when off the throttle when no injection taking place. If you can't place it top or bottom by listening pull the cam cover off and have a real good look, then test oil pressure see if that's down with worn shells etc.
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how do you test the oil pressure?
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Well, my mechanic isn't quite sure either, he says it could be something in the cam area, but thinks it's too loud for that and therefore likely the little end maybe breaking up. Basically no way of telling without taking stuff apart. I'm inclined to think this is bottom end to be honest, so what I'm planning to do is, at the weekend, I'll flush the engine again, now the clean oil has been in it for a week, then depending on what happens during the flushing stage (i.e. if the noise goes away or not) I might take the sump off while it's up in the air and have a look at what's what.
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im getting a really bad feeling that it is the big end if it is ill have no choice but to throw the car away, not going to buy another engine for it. From what i remember taking the sump off will tell you straight-away if the big ends are shot?
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Sounds like bottom end to me..
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Originally Posted by bear1 View Post
im getting a really bad feeling that it is the big end if it is ill have no choice but to throw the car away, not going to buy another engine for it. From what i remember taking the sump off will tell you straight-away if the big ends are shot?
All depends just how shot they are, but yeah, removing the sump should give me a clue. It's definitely not big ends, because there is no apparent loss of compression or smoke, or in fact any tell tale sign other than the knock. So it's either little ends, bearing(s), shell or a rod, guess we'll see.

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Sounds like bottom end to me..
Yeah unfortunately. Guess we'll see at the weekend when I get the sump off. Depending how much the bits are and how quickly I can get them, dictates whether I just buy a £400 engine off ebay or repair this one.

I'm not going to replace the entire bottom end and faff around, if I repair it I'm just replacing whatever is broke, lol. That won't make it last the longest I know, but it was a £500 car, my repair limit is around £500 before it becomes not worth it.
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Originally Posted by HollowPoint View Post
It's definitely not big ends, because there is no apparent loss of compression or smoke, or in fact any tell tale sign other than the knock
Big-end shell going shouldn't affect compression or emit smoke .. it will manifest itself as a knocking/rumbling sound which gets louder as you rev and as the oil warms up and thins.

If it's a tapping sound, it's not likely to be the big-end .. it's more likely to be top end. Not familiar with a diesel engine and how it's constructed, but it's possibly the cam or rocker related. Don't think it uses hydraulic cam followers (or does it?). Might be the little end (piston pin end of conrod).

Have you tried the old mechanics trick of placing a long screwdriver or metal bar against the engine and pressing your ear against the handle/end? Move the screwdriver around on the engine until the noise transmitted through the screwdriver is loudest. Or even a stethoscope if you can get hold of one!

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Big-end shell going shouldn't affect compression or emit smoke .. it will manifest itself as a knocking/rumbling sound which gets louder as you rev and as the oil warms up and thins.

If it's a tapping sound, it's not likely to be the big-end .. it's more likely to be top end. Not familiar with a diesel engine and how it's constructed, but it's possibly the cam or rocker related. Don't think it uses hydraulic cam followers (or does it?). Might be the little end (piston pin end of conrod).

Have you tried the old mechanics trick of placing a long screwdriver or metal bar against the engine and pressing your ear against the handle/end? Move the screwdriver around on the engine until the noise transmitted through the screwdriver is loudest. Or even a stethoscope if you can get hold of one!
On most cars, the big end going will make it loose compression (Albeit only a little until it really does go) and on a diesel, should produce a fair bit of smoke because of the lesser compression. I think it has hydraulic cam followers, but I don't know this engine at all yet, so maybe not.

Haven't tried that trick yet, one of my favourites too, but I haven't even had the plastic top cover off the engine just yet, I will be doing. I'll be disconnecting the injector plugs one at a time too, see if the noise continues or goes away. I might do that tonight if I get time and can brave the cold long enough.

I have a nasty feeling it really is bottom end related, the guy at Auto Lusso reckons the big ends are the most common to go on this engine, but will just have to do some more diagnosis and find out. Think tonight will be injector plug removal and the screwdriver test, shoot out to Halfrauds and pick up some more flush, oil and filter then on Saturday I think I'm going to do the flush again and if the problem still isn't solved, I'll pull the sump off to confirm bottom end.

I did see a piece of shiny metal in the oil pan when I did the last change, but I had to muller the sump plug to get it off for one thing and for another we only just broke a car for parts a few weeks back, so there are plenty of shards around the garage, could have been from either tbh. Guess I'll do some more testing and come back to you all, lol.
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The tappets are solid with shims, not hydraulic. Our 2.4 courtesy car's bottom end let go at 160-odd thou but the oil that came out of it was like sludge, God knows when it was last changed, so I think that was the culprit.
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Yeah just been on the phone to one of the guys at Auto Lusso again, this time a tech though. He says the only time the 2.4 tends to go, is when someone knocks the sump off at the bottom and drops the oil.

Sludge-like oil would definitely do that too, I've seen it, not pretty, lol.

Supposedly these bottom ends are rock solid and barely EVER go, so speaking to the guy at Auto Lusso I am now wondering if it might be that someone just screwed up installing the new injectors, potentially one of them is just pouring diesel into the cylinder at all times, rather than bursts.

Supposedly top end problems on these engines are common, bottom end are rare as hell. This one has done a good 150k+ though, so I just dunno. Going outside now to test the injectors, see what I come up with, fingers crossed that's it, because funnily enough, the tapping started to get worse when I first put the diesel cleaner in it, then gradually got louder and worse. Potentially as the diesel cleaner worked it's way through the system?

Just went and put some different diesel in it and topped up the oil (Only just realised needs 5.5 litres, I only put 5 in, but that wouldn't cause this) and some more diesel cleaner, doesn't seem any different yet, but the missus is going to take it to work tomorrow, 100 mile round trip, if anythings gunna sort it or kill it, I reckon that'll be it, lol.
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Yeah just been on the phone to one of the guys at Auto Lusso again, this time a tech though.
Did you get the name of the person you spoke to? The techs only really see the problems that people bring to us to fix, I've seen a few over the years that have had bottom end problems and I've also sold a few cranks & oil pumps for 2.4 JTDs.. Top end problems are usually cambelt failure, injector troubles etc. We do tend to see more of these but I think partly the reason for that is that they are cheaper/easier to fix, whereas if the bottom end goes then people just tend to get rid of them.

If one of the injectors was leaking fuel into the cylinder, would it be possible to leak enough to be partially hydrolocking that cylinder, causing the knock? I think if that much fuel was leaking through though then you would get lots of smoke.

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Leaky or incorrectly atomising injectors will cause a knock, as said they will also cause a lot of smoke and usually a misfire. It usually also stops when off the throttle and no injection
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Originally Posted by Pud237 View Post
Did you get the name of the person you spoke to? The techs only really see the problems that people bring to us to fix, I've seen a few over the years that have had bottom end problems and I've also sold a few cranks & oil pumps for 2.4 JTDs.. Top end problems are usually cambelt failure, injector troubles etc. We do tend to see more of these but I think partly the reason for that is that they are cheaper/easier to fix, whereas if the bottom end goes then people just tend to get rid of them.

If one of the injectors was leaking fuel into the cylinder, would it be possible to leak enough to be partially hydrolocking that cylinder, causing the knock? I think if that much fuel was leaking through though then you would get lots of smoke.
It was me he talked to

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Did you get the name of the person you spoke to? The techs only really see the problems that people bring to us to fix, I've seen a few over the years that have had bottom end problems and I've also sold a few cranks & oil pumps for 2.4 JTDs.. Top end problems are usually cambelt failure, injector troubles etc. We do tend to see more of these but I think partly the reason for that is that they are cheaper/easier to fix, whereas if the bottom end goes then people just tend to get rid of them.

If one of the injectors was leaking fuel into the cylinder, would it be possible to leak enough to be partially hydrolocking that cylinder, causing the knock? I think if that much fuel was leaking through though then you would get lots of smoke.
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Leaky or incorrectly atomising injectors will cause a knock, as said they will also cause a lot of smoke and usually a misfire. It usually also stops when off the throttle and no injection
There's no smoke and no misfire and it continues on tickover. I got the old screwdriver out tonight and it sounds like it's the cylinder closest to the gearbox, I also found out the guy before me only replaced the injector furthest away from the gearbox and replaced an o-ring seal on the one next to that.

Un-plugging the injector does seem to get rid of it a bit, but not entirely, so I'm gunna say it's bottom end at this point. It's definitely not top end that's for sure now. There's potential for hydrolocking, but I'm doubting it heavily at this point. I think I'll drive it until it throws something through the side of it, then buy a replacement engine and just drop it in. I'll flush it again this weekend as planned, if I feel so inclined at the time, I'll take the sump off and have a gander at the internals, if it looks terminal (Thinking it will tbh) then I'll sort out an engine sooner rather than later so it's here to drop in as and when I get time or it's needed.
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