Hello All!
So long story short, I'm a newer member, bought my 2003 Discovery knowing it has an engine noise but now I need to figure out what it is so I can go about fixing it. It's making a tapping noise only when it gets to operating temp, dead silent when started cold and for about the first 5-10 minutes of running. As of right now I have the top decently torn down and have an inspection camera coming in the mail. I thought it might have simply been a broken rocker arm or something obvious once I pulled the valve covers, but still don't see anything obvious wrong. Maybe I've got a liner or 2 wandering around? If I stick the inspection camera in the cylinder would I be able to visually tell if one has slipped around or not? Just trying to get myself a game plan so that I can make 100% sure I get the problem fixed the first time around. It's a pretty dang loud tapping and everyone stares as it drives past hahahaha. Thanks in advance for any light anyone might be able to shed on the situation!

 

I doubt you will be able to see a slipped liner with the inspection camera.

 

You need to remove the heads and run your finger nail across the liner/block seam. If you feel a ridge at the seam it's dropped or proud of the bore. Straight edge (machinist rule) works too, looking for daylight under the rule. A dial indicator on a beam works too. Measure the block deck, measure the liner height. Usually when they travel with the piston you'll see a pronounced seam (darker, larger) whereas between one that doesn't move the seam will almost disappear against the block. Coolant will cause discoloration at the seam, it's another sign it's moved.

What I would do since you know it has a high probability for liner movement already why not just have the block top hatted and be done with it? I'd toss some other goodies at it as well and then button it up and call it better than new.

 

Gotcha, that's what I wondered if it was going to be obvious enough to see it with the naked eye or not. I literally just bought this thing as a toy so I'd rather have the least amount of commitment to get it going decently. Going for that low hanging fruit first before I dump a ton of my time into it for what might be no reason yet, that's all. But yes, I agree if it does in fact have a liner moving then the entire thing is definitely getting pulled and machined for flanged liners. Anyways I'll keep you guys updated, I just got my camera today and I have a 180* t stat to put in, also going to retorque the rocker arm shafts etc to see if that changes anything. I figure it can't hurt, I've definitely heard a few of them with what sounds like the exact same noise and they were curable by simply changing the oil and putting in the lower temp t stat.

 

Sometimes it is and sometimes it isn't obvious. The other issue with the 03/04 blocks is cracks behind the liners which again might be or might not be obvious. Being over ten years old there's a chance it's poor oil changes that have rockers a knocking and I guess you'll know when you know. I went through my engine the first time I cracked it open and found all kinds of neglect including occluded oil galleys all throughout the top end to include the rockers themselves. I was fortunate enough to get to it when I did otherwise there would have been a sure failure.

 

Yeah, well that's what I'm hoping for is literally something just that simple before I go yanking the entire thing out of there. I did check the rocker bolt torques, all correct, none loose. Like you're saying though with some of the neglect issues, this may be along the same lines. Places around the rockers where the oil has a tendency to puddle it's extremely sticky like burnt oil or honey, but dark brown/black. My guess is that most of the oil passages are probably about the same so I'm going to tear the rocker arms all down and pull the pushrods to clean them all up, then I'm thinking just reinstall everything real quick to see if I've in any way changed the noise at all, then go from there, maybe a good can of seafoam? Lol.

Also another weird thing that I forgot to mention before is that even with the loud tapping/knocking, the knock sensors aren't picking up anything at all. It even passed smog knocking away like crazy. Just found that peculiar and maybe a really good clue however I'm not really sure what that would mean for sure.....

 

you will not see a slipped liner with an inspection camera, but what you probably will see is a nice shinny piston.

If you have one of two pistons that are not black like the others, then they are being steam cleaned somehow.

as long as you have the camera you have nothing to lose

 

Yep! I was buying the camera regardless because it just seemed like it could have a zillion other uses. I pulled all the plugs and peaked down into each cylinder, every one seemed extremely consistent with one another, none shinier than the others, all just look exactly like any other motor with 100k miles that I've pulled apart. No mixing of fluids either, all the coolant I drained was very clean, same with the oil, other than just being rather old there was no milky or sludgy to it, no coolant smells. At this point I figure I'll clean what I can and put it all back together and if I still can't get it to quit then out she comes for a complete teardown and rebuild!

 

If you can, perform a compression test on the engine fully warmed up. I'm not saying it's the be all, end all but it might give you readings on cylinders to look at if you do pop the top. The compression test is one of my favs because of the high pressure.

When you look at the push rods they're supposed to be round like a ball, not mushroom shaped. Rockers oil from the shaft to the rocker to the push rod cups. That's where I found mine occluded, hard carbon. A soak in Chemtool did most of the work on em. A dental pick did the rest. Also looking for missing buttons on the rockers, they contact valve stem, spin it. Not uncommon to find one missing.......... clack, clack, clack.

 

Well I went ahead and took the rockers off tonight. Haven't had a chance to actually tear the shafts and rockers themselves down, however they all seem ok enough to where I wouldn't think they should be making the kind of noise this thing is making. Anyways, one thing I did notice is that the pushrods are a bit worn/mushroomed like you had a said. I measured one of the worst ones and saw about a 20 thousandths difference in diameter between the top and bottom of the pushrod. Still, not sure that's really enough to cause my noise (which if it were in anything else I would be convinced was simply rod knock). I didn't see any obstructed rocker arm oil passages, at least near the pushrod seat, the openings all appeared clear, and I'm not missing any of the buttons on the valve stem side and wear on those appears normal and pretty consistent. Any other ideas before I try putting her back together? I figure pulling the heads will be saved for another day if I put it back together and the noise remains. Also, again about he knock sensors not picking up the noise, is it just a possibility that maybe the noise is coming from the oil pump/timing cover and it's just not close enough in proximity to the sensor to cause it to retard the timing? Ever heard of that making noise like that? Thanks for all of the awesome help so far by the way, I at least feel like I've got some direction now other than just simply tearing it 100% down and hoping that completely rebuilding it takes care of the issue, lol.

Before I forget, those rocker mounting bolts, are those a torque to yield bolt? I didn't think they were but I can't remember off the top of my head so better safe than sorry, haha.