Long time MB/BMW Tech here with first experience in LR's.

So I bought this '95 Discovery with 172K on it for the girlfriend. I checked it over, everything seemed hunky dory except for a slight valve tick. No big deal. Well about a month later we head out to do some camping, I get in it and there it was "the dreaded knock!" Not sure how, butshe has grenaded every engine she lays her hands on...

So here's the deal, lets see what you guys know:

-The guy that had it before changed the oil with 5w-30 syn.

-After I discovered the knock I changed the oil and put in 15w-40
A. I sawit recommended on another forum.
B. Thought it might help me figure out what the knocking was.

-The knock starts after the car is warmed up and under slight load (1/4-1/2 throttle). Will do it underload standing still as well (power braking).

-I put an oil pressure gauge on it. Got about 38 psi cold and about 32-34 warm at about 2000rpm. Right around 20 psi at idle warm.

So I'll make this multiple choice:
A. Rod Knock
B. Main Bearing
C. Wrist Pin
D. Loose Bolt on Flex disc
E. Bent Push Rod
F. Something in the trans
G. other suggestions

If it is a rod knock:
What's the best way to go about this (Cheapest and Easiest)?
A. Can I drop the pan and throw some rod bearings at it?
B. Pull the whole engine and do pistons, mains, rod bearings, rings etc?

 

A. Could be a rod knock. From what you're discribing, it's very possible
B. Main bearings usually make noise only at start up when oil pressure is low. Once pressure buildsmain bearing nosieusually goes away.
C. Wrist pins can have the same knocking noise like a rod
D. Loose flex bolt is also another possibility, but since we're dealing with a Land Rover withtheir infamous oil pressure, oil sludge problems,I wouldn't think it's not a loose flex bolt
E. See answer D.
F. See answer E.
G. My only suggestion is to do a cylinder cut-out while the engine is knocking. Simply disconnect a spark plug wire or fuel injector harness one at a time to see if you can isolate which cylinder is knocking. If you disconnect the plug wire or fuel injector harness and the knocking stops, you've just found the which cylinder to concentrate on.

I just purchase a Disco that had excess sludge from top to bottom. Oil pan, oil pick up tube, rocker shaft assembly, engine valley lifter areaandvalve covers. Unlike yourself, I had less than 10psi of oil pressure, which slowly droped as the engine got hotter.

99.9%of vehicles(engines) on the road you can drop the oil pan and change rod bearings with little to no problems. Fortunate for you (and me)Land Rovers are no different.Here's a pic of myoil pan removed showing easy access to the rod caps.



I haven't had a chance to check my rod bearings, but that's definately on the to-do list.

If it does turn out to be a rod knock, I wouldn't necessarily pull the engine fora mild to complete rebuild.There are a lot of other variables I would consider before pulling the engine.

[ul][*]What's your intent for the truck[*]How long are you planing on keeping it[*]Sounds like your mechanically incline, so you would probably will be doing your own work.[*]Do a compression test. Better yet, do a compression test and a leak down test. That will tell you how efficient your cylinders are sealing.[*]If all those look good and it's just the rod bearings, why pull the motor. [/ul]
I have a detail thread in the Disco section showing my adventures with mytruck from day one

Good luck

 

generally a rod knock will present itself right off idle, itll be a double knock, blip the throttle cable and see if you can hear it then. if its only happening under a load, you might want to check youre not dealing with detenation, what kind of gas, wheres your timing set at. main bearing will be a single knock, and usually these engines either dont throw mains, or spin them and youre done, not much grey area on those. wrist pin and rod will be double, cut cyl to check where as said above. seen these flex plates crack, itll be a make noise at more random intervals, and as for push rod, thatd be top end, more of a valve click

 

Thanks for the input. I was leaning toward your suggestion on the rod bearing replacement. I just freak out after I do a 4 hour job and I drive it down the road to find out that it was something else! So....I literallybusted out the engines 101 book from mechanic school. Here it is verbatum.

Crankshaft bearing:
"Sound Identification: Dull, Heavy pound or thud - especially noticable during periods of heavyengine loading. Frequency is related to crankshaft RPM. The loose bearing may generally be isolated by shorting spark plug. When the plugs inline with the affected bearing are shorted the sound will change."

Connecting Rod Knock:
"Sound Identification: The connecting rod is usually more evident when the engine is floating(not accelerating or holding back on compression) at speeds around 30 mph(48km/h) in direct drive. The knock, a regular light metallic rap, can either be eliminated or greatly subdued by shorting out the cylinder concerned."

I wanted to do the mains because I saw "under periods of heavy loading" in the crankshaft bearing section; however, while writing this I got to thinking that it doesn't occur under periods of heavy load. It stops when I floor it. It happens more at like 30 mph under slight load. Not heavy. Also, I don't think it's so much a "thud" as it is a "rap." SO...with all that I'm gonna:

A. drop the pan
B. clean out the poo
C. check therod journalsforout-of-round
D. replace the rod bearings
E. get back on here and lay blame to everyone else if this doesn't fix it

Question 2....
Valve tap.
A. Think I can replace the affected lifters/push rods or you think I need to replace them as a set. Since they're supposed to be lapped in with the cam.
B. How might I go about figuring out which lifters/push rods are the culperates?


I'll get some video of this noise. That should make things way cooler!

Thanks for the help guys! I'll let you know how everything goes....

 

Problem Solved!

I started pulling plug wiresand the noise started changing. I noticed it changed whenever I messed with a plug wireon the right bank. So I pulled all the plug wireson the right bank. The Catylist got red hot and the noise went away. So I let it cool down and tried it again. This time with me under it. And sure as ****! There it was the cat was rapping away just like a rod. I pulled the plug witresagain and got the cat red hot again and the noise has all but vanished! THANK GOD!!! I tried to get some footage so you guys didn't think I was nuts, but the noise went away. I'll post up a video if/when the noise starts again. I've heard alot of cats rattle around in my day but never one that sounded just like a rod. It's in tune with the engine and everything. CRAZY! Well thanks for everyone's input and help.

 

coincedence??? as to the cat gettin red hot, youre dumping fuel into a hot cat when you remove the spark. call me a skeptic, but im iffy at best with your fix man

 

I think he realizes the final fix will be a cat replacement.

BTW, yes you're lucky.