This is interesting and proves that not all ticks are indeed from the liners.

Simple and straight fact - if there are no tell-tale signs of grooves in the gasket firing rings, then the problem is not liners.

Now is the easy part: Continue disassembly until you find the problem. I actually think you are in a great position to find the noise, and to basically rebuild your engine to be as good as new and ready for another hundred thousand miles -something that you wouldn't have been in a position to do if you had never pulled it.
If you haven't got any already, invest in a set of digital calipers. Sure, Mitutoyos are nice, but even harbor freight ones are accurate to 1thou, which is enough for what you are trying to measure.


So, here are some of my thoughts.

Oil pressure is not going to cause the noise unless it is so low all the time that your engine is on the verge of death. Sire, replace the pump gerotor, but also pull the relief valve and make sure you clean all the pump galleries out - basically get the front cover down to the bare casting!

These are what you need to concentrate on inspecting in the engine:

Camshaft (wear on lobes and journals)

Camshaft Axial thrust plate (present, tight, not grooved / worn)

Cam bearings (all 5 - are they worn, are the oil holes aligning with the oil holes in the block?

Rockers / rocker shaft (any major free play? Are the steel seats present and not loose)

Pushrods (bent, are all the same length)?

big-ends (remove rod from block, re-asseble with shells and check diameters then compare to the crank journal diameter it came from.

little ends (check if worn)

piston skirt clearances ( do they still have the machining grooves in them or are they scuffed smooth? Do a quick measurement check and compare to the bore diameter)

Crank: inspect very carefully - all journals and thrust faces. check all oil holes are clean and free of crud. Measure all journal diameters. If they measure up, do the fingernail test to see if it needs regrinding. If they are still ok, I totally reccomend having it micropolished at a machine shop (circa $65). Before any of the above though, screw the front bolt into the crank. Suspend it vertically by the bolt with one hand, and do the "ding" test to make sure it is not cracked - if not sure, have the machine shop do a magnaflux on it (circa $50)

Block Bores: Have a machine shop inspect diameters. From what the UK rover experts say, the bores rarely wear - indeed my old bores at 115K ish miles were still right in the middle of the tolerance zone... Have them perform a very light hone - DON'T do this yourself with the nasty tool from autozone LOL, do it on a real machine.
Before doing this, you might want to go ahead and pin the bores - perhaps in anticipation of something that although hasn't happened yet, might happen some point down the line, and would be a real pisser if you didn't take a few hours of your own time with a drill, tap and screws to do it yourself at the best possible time (block naked and on the workbench) to do it...


Block: Remove the plugs from the lifter oil galleries at the back of the block and use the long brushes (like gun cleaning brushes) to make sure these are clean and free of crud. Also shine a light down there and check the lifter feed holes are clean, not burred up or in any way restricted. Check the fit of the (old) lifters into the holes they came out of - excess radial clearance will mean oil will dump down around the lifter instead of pumping it up... Next, have the machine shop do a full cleaning on the block. Fit the new main bearings to the block (without the crank in place) torque up per the manual including the side bolts, and have the machine shop measure diameters on the bearings. Now compare these numbers to the crank journals you measured and make sure you aren't running excess clearance. Sure, you can use plastigauge, but this is the most accurate way to do it!

Have the deck inspected - while this far in, perhaps it might be better to have the shop do the lightest skim possible to make sure all is perfect - this is definately optional and depends on what the decks look like.

Measure the width between the thrust faces across the centre-main, and compare the the crank to verify your clearance before putting it all together.

Finish by chasing ALL the threads in the block so re-assembly will go as planned.

Heads: Just had these over to the machine shop, along with new stem seals and tell them to re-face the valves and seats and fit the new seals. May as well give them the lightest skim needed to ensure they are perfectly flat. Typical cost will be $250-$300.


What else? Well, go ahead and replace all the lifters regardless - these are cheap and notorious for being a source of noise. Some will say to replace the cam as well - but if it is perfect (as my original cam was at 115K) does it make sense to replace with an aftermarket cam? Some say cam MUST be replaced, but I personally disagree and have run many tens of thousands of miles on engine where I only replaced the cam or only replaced the followers - it all depends on your budget... Also replace the chain regardless, and chainwheels if they show any sign of wear.

I would only fit OE main bearings - I got mine from thse guys, no-one came close to the price for OE stuff: LAND ROVER CONNECTING ROD BEARING SET STD RANGE P38 DISCOVERY STC1426 FEDMOGUL | eBay
As regards the pistons- unless they are badly scuffed, I'm sure you won't need a rebore or oversized, so you will need a set of "standard" rings. Shop around for a good deal on these - OE is ridiculously expensive, so I would go aftermarket.
If you buy the gasket set from roverparts then it WILL come with GENUINE elrings. I got duped by a seller once who claimed his kits had elrings, well - if they don't come in a package with Elring written on them, and an Elring hologram on the package, they probably are Elring clones. Sure, they might work, and there is probably a very believable story about how they buy in bulk, and get them unpacked, blah blah, blah - well so do roverparts, but they somehow do get pukka items.

Finally, get a set of ARP studs to hold it all together.

You might go though all the engine and not find the "smoking gun". You might find two, maybe three "possible causes". What you do need to do is inspect everything - the worse thing you can do is believe you find the problem and be less than carefull in continuing inspecting everything. If you check all I've said above - at least you know the engine has gone back together in such a manner that it will not make a ticking noise... If you are committed enough to remove it and tear into it, then I'm sure you'll be commited to do the rest of the job properly....

 

the short version of above would be to completely rebuild the motor.

 

Different folks have diffrent opinion on what Rebuild means. Some guys replace everything, even the pushrods. Others insist on a +10 on all journals and new pistons, even if the old journals and pistons were perfect...
The above is simple to do and low cost. A true rebuild is definately not low-cost.

 

I did my oil pump, timing chain, gears on my 03. Tick is still present and bothers me like crazy, especially because my old RR runs as smooth as a turbine at all temps. The tick is not consistent with the sound of liners. It sounds terrible from cold, and progressively sounds better as it heats up. In neutral, at 2-3k rpms, it makes a terrible gargling slapping noise. If I had to make a guess, I would say its the cam-shaft, rocker arms, or lifters being worn from long exposure to low oil pressure. I was in an 04 Disco at auction last week that was very smooth, no ticks, had similar miles on it. Had an 01 Disco for a couple months (what a POS that was), sounded the same if not a little worse than the 03 I have now. Similar miles too.

I'm too lazy to do a complete tear down of my Disco. I guess if other ones out there sound similar and just keep going, mine will too. I stopped worrying about it, my disco has had all the major issues addressed, holds oil pressure just fine, doesn't over heat (temps between 194 and 201F) or lose coolant. So I guess I will just keep driving it.

I am very interested to see what else you find though 0304Disco. Keep us posted .

 

I did find both intake and exhaust lifters for the #3 Cyl that had some marking on the faces that could be indication of them flattening out and making the awful tick. The pushrod surface that makes contact with the lifter on one also had wear unlike any of the others indicating some abnormal movement. The lobes look good and measure out within all others. I'm replacing the two lifters for that Cyl along with the pushrods. I know you'll get many opinions on if you can replace just the lifters and not the cam. I'm doing it and will say my prayers that I can get another 60K on this beast.

Cheers