Mysterious knock or loud tick in engine

Hello:

The car:
A 1998 P38 4.6 HSE full option with close to 200,000 miles on it. It has always been serviced to the letter by an official Land Rover dealer. I have it a few years and have driven it for about 35,000 miles. My foot is on the heavy side, I always drive in Sports mode and do not shy away from the occasionally flooring it. The engine runs fine, no oil burning or undue noises or smoke -- until now.

What happened:
While merging into a main road I put the throttle a bit more than 3/4 down. All of the sudden it makes a sort of rattling noise, a bit like the fanshroud hitting the fan. I immediately lift the throttle and the noise goes away. As soon as I load the enige however it returns. When I stop and open the hood, nothing seems amiss save a faint ticking sound which becomes louder when I rev it cautiously. I am able to limp home (about 10 miles). I have the impression that, by now, it is louder and more like a flappin or loud ticking. It is not a rod which is deeper in tone and originates from the bottom, it is not like a broken piston neither. It is more like a valve, a flat piece of steel acting as valve, which closes violently, slamming against its seat.

Symptoms:
The noise seems to come from somewhere under the inlet manifold. It does not seem to originate from within the valve covers. We are unable to locate it positively, even not with an automotive stethoscope. It is not directly related to the revs and is not synchronous with them neither. It is not constant even, it goes tak tak tak and then all of the sudden taketaketak, not always the same order. It becomes very loud when the engine is loaded however. The engine rocks very gently, almost inperceptly on idle in drive with the AC on indicating a pretty even combustion in all cylinders.
I took off the inlet plenium and did not see anything out of the ordinary save that the air "trumpet" of the 8th cylinder was a bit black with soot, the others were just the normal slightly oily black. with no soot.

Additional info:
Recently the engine was severely overfilled by an @#$%#@ of a mechanic. Depostits in the engine came loose and at one point the oil pressure light came on and the valves started ticking. The engine was immediately stopped and the car towed to the shop. The the pan was removed and the mesh on the oli pump cleaned, also the sump. New oil and a new filter were installed. This is alreay about a thousand of miles ago.
What could this be ??
One theory is that an hydraulic lifter got some dirt in it and did pump up too high, the valve got hit by the piston and is now bent. This could explain the soot on cylinder # 8. If the valve is very slightly bent then the engine would still run pretty evenly. BUT this does not explain what the noise is and certainly not why it is not synchrone with the revolutions. The noise defenitely does not originate from that corner, it would more be like in the center or towards the # 1 cylinder but then still under the manifold. (I know I first should measure the compression but had no time yet ).

About me:
I am a professional mechanic with 40 years experience on all sorts of cars, rebuild numerous engines from basic to Lotus 16 valve, Jaguar 6 es and Maserati DOC V8's. I mention this not to boast but to put my story in perspective, I know what I am talking about. This however is something I never heard of nor experienced, maybe somebody had a similar experience or a suggestion.

Any help/suggestion is more than welcome

Thank you

Andre

First job compression test. With your experience surprised you came on and asked that. If you can't sort who the hell can? All the lifters should be compressed before refitting in the engine and allowed rest then turned by hand to check for fouls before startup you should know that.

little end?

Liner starting to slip?

StuckAgainSteve said:

Liner starting to slip?

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A possibility, a man of his skills a head off, sump off and piston out

wammers said:

First job compression test. With your experience surprised you came on and asked that. If you can't sort who the hell can? All the lifters should be compressed before refitting in the engine and allowed rest then turned by hand to check for fouls before startup you should know that.

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I say it in the post, I should do a compression test but had no time yet. And a compression test will only tell me which cylinder is faulty, the fault iI should be able to see when the head is off but still not the cause. I thougt this is maybe a thing which is common to these engines.

StuckAgainSteve said:

Liner starting to slip?

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The engine did not overheat and I do not have any loss or contasmination of fluids

Hello:
At this point it seems to be that nobody had an experience like this before. I thank all for their suggestions but would like to ask, unless you experienced this phenomena firsthand, to refrain any further posting at this point untill I post the results of the compresison test and the sparkplug color.
Thank you
Andre

Well I have experienced a Rover V8 engine with a weird tick years ago, it was assembled after a rebuild with the cam timing 1 tooth out.

andreh said:

I say it in the post, I should do a compression test but had no time yet. And a compression test will only tell me which cylinder is faulty, the fault iI should be able to see when the head is off but still not the cause. I thougt this is maybe a thing which is common to these engines.

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To be honest my friend with your posted experience you should not have needed to ask the question. You should just have got on and sorted it. It's much the same as any other engine the crank goes round and the pistons go up and down the valves open and close. Repairing them is simplicity itself. Just get on and do it.

Unlikely to be a broken valve - this will make a loud noise at all engine speeds - speaking from experience

And I second what others have said - there are several places to look for common faults, so you could do that - you'll quickly find out what's common and what's not. But when you get stuck, or hopefully work out what went wrong and how to fix it, then post here - I am sure others would be grateful, or at least interested in your story.

wammers said:

To be honest my friend with your posted experience you should not have needed to ask the question. You should just have got on and sorted it. It's much the same as any other engine the crank goes round and the pistons go up and down the valves open and close. Repairing them is simplicity itself. Just get on and do it.

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OK, tell me where to start, take off both heads ? Chances are indeed the I see more, like a loose liner = unecessary work as enigine is trash. Chances are that I see nothing. It is just to maximize efficiency that I ask your knowledge base, more know more and this is something I never experienced nor heard of, apparently unheard of in Land Rover circles as nobody could give a coherent answer so far.
It is not my habit to take out the engine to replace the sparkplugs so to speak (except with the first generation Porsche 911 Turbo where is was almost a necessity). I want to have a fair idea of what it could be what is causing the trouble.

awillemsen said:

Unlikely to be a broken valve - this will make a loud noise at all engine speeds - speaking from experience

And I second what others have said - there are several places to look for common faults, so you could do that - you'll quickly find out what's common and what's not. But when you get stuck, or hopefully work out what went wrong and how to fix it, then post here - I am sure others would be grateful, or at least interested in your story.

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I know many things make sense and then are countered by others. Like the absense of any knock the first few seconds after starup, this could indeed point to a loose liner as could the unsynchronized frequency. But this is countered by the fact that the car has been driven for more than 60 miles now in that condition, it does not overheat, nor did before, and there is no metal shavings nor contamination or whatever of the oil. I will look further into it and keep you posted.

andreh said:

OK, tell me where to start, take off both heads ? Chances are indeed the I see more, like a loose liner = unecessary work as enigine is trash. Chances are that I see nothing. It is just to maximize efficiency that I ask your knowledge base, more know more and this is something I never experienced nor heard of, apparently unheard of in Land Rover circles as nobody could give a coherent answer so far.
It is not my habit to take out the engine to replace the sparkplugs so to speak (except with the first generation Porsche 911 Turbo where is was almost a necessity). I want to have a fair idea of what it could be what is causing the trouble.

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If it's engine speed it's crank, rods, pistons. If it's half engine speed it's cam, followers, pushrods, rockers, valves/springs. What else do you want me to say? My crystal ball is away for service.

wammers said:

If it's engine speed it's crank, rods, pistons. If it's half engine speed it's cam, followers, pushrods, rockers, valves/springs. What else do you want me to say? My crystal ball is away for service.

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I know, my ball too it fogged up. The fact is it is NOT in sync with the enige speed, so it is NOT crank or camshaft related not valve related. It IS load related, gets louder with engine load. It is not even constant, sometimes it knock at a steady rithm and then, all of the sudden accelerates the rithm without relation of the engine revs.
I considered a loose liner as this is one of the weak spots of these engines. But after nearly 200,000 troublefree miles and without ever overheating ? The noise starts only after a few seconds at starup, which could be consistent with a loose liner (I guess as this mishap is not in my experience). BUT this is countered by the fact that the owner drove it for over 60 miles, albiet at reduced speed = less than 60 miles ! The car did not overheat nor did things got worse. Also the oil is not contaminated in any way. And the car idles still pretty smoothly, so smoothly in fact that a layman would maybe not notice it, but surely not complain. This is NOT consistent with a loose liner. :scratching_chin:
I am at a loss and that's its why I try to consult the knowledge base and you christal balls and experience in the hope that somebody had this before and could tell me: "oh that's the gizmo from the whatsmesit which knocks against the thinghy, you just have te retighten it . . ."

andreh said:

I know, my ball too it fogged up. The fact is it is NOT in sync with the enige speed, so it is NOT crank or camshaft related not valve related. It IS load related, gets louder with engine load. It is not even constant, sometimes it knock at a steady rithm and then, all of the sudden accelerates the rithm without relation of the engine revs.
I considered a loose liner as this is one of the weak spots of these engines. But after nearly 200,000 troublefree miles and without ever overheating ? The noise starts only after a few seconds at starup, which could be consistent with a loose liner (I guess as this mishap is not in my experience). BUT this is countered by the fact that the owner drove it for over 60 miles, albiet at reduced speed = less than 60 miles ! The car did not overheat nor did things got worse. Also the oil is not contaminated in any way. And the car idles still pretty smoothly, so smoothly in fact that a layman would maybe not notice it, but surely not complain. This is NOT consistent with a loose liner. :scratching_chin:
I am at a loss and that's its why I try to consult the knowledge base and you christal balls and experience in the hope that somebody had this before and could tell me: "oh that's the gizmo from the whatsmesit which knocks against the thinghy, you just have te retighten it . . ."

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Sorry mate i don't know. Sat here as i am and the car with you it is almost impossible to guess what it could be. Could it be vibration related? If it is touching things with a screwdriver when the noise is there could find it other than that i am as wise as you are.

wammers said:

Sorry mate i don't know. Sat here as i am and the car with you it is almost impossible to guess what it could be. Could it be vibration related? If it is touching things with a screwdriver when the noise is there could find it other than that i am as wise as you are.

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No problem, i know it is next to impossible unless one experienced a similar thing. And NO, it is not vibration related. And, strangly enough, we cannot locate it not with the screwdriver trick nor with an automotive stethoscope. it oroginates "somewhere" under the inletmanifold, from the engine or what, impossible to say. :scratching_chin:

Something else, a few years back, well about 10 to 12 I helped build a Staggerwing from a Griffon kit, quite interesting and a gorgeous plane with interesting stall behaviour. :cool2:

andreh said:

No problem, i know it is next to impossible unless one experienced a similar thing. And NO, it is not vibration related. And, strangly enough, we cannot locate it not with the screwdriver trick nor with an automotive stethoscope. it oroginates "somewhere" under the inletmanifold, from the engine or what, impossible to say. :scratching_chin:

Something else, a few years back, well about 10 to 12 I helped build a Staggerwing from a Griffon kit, quite interesting and a gorgeous plane with interesting stall behaviour. :cool2:

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I was not suggesting putting the screwdriver to your ear. But putting pressure on components with it, sometimes a loose heat shield Etc will cause an intermittent noise.

@ this point it must be allowed to throw in a wild guess - clutch or area

Perhaps it's exhaust related. When the weld on the collar of the pipe to manifold failed on mine it made weird intermittent noises until it broke completely. It was easy to figure out after that.