97 disco 4.0 tick / soft knock

[mspeters]

My trusty 97 D1 has slowly developed a tick or knock over the past 2 years. My ears are trained to Cummins and VW IDI diesels...hard to discern.

I could use a well-trained ear to get a reading if this is the common rocker arm wear out or the dreaded slipped liner. It just completed a 800 mile trip in Nevada over Jefferson and Ophir Passes w/o incident, less a pin holed ARB air hose.

Noise is somewhat intermittent. More so when warm, although it can make the same sound when cold. It sounds like a fluttering soft knock, and echos via the oil pan. Stethoscope on the valve covers is not discernible to which bank. Just a bit of throttle to 1200 RPM and the noise fades. I detect no knocking when under load.

http://youtu.be/VfRuV2HOz_U

Owned since new. 97K miles, all on synthetic oil. Few problems besides 2x water pumps and tensioners, 2x alternators, and a timing and valve cover gaskets. Only used for Nevada camping trips now. I recently had the oil pan off to change the timing cover gasket. zero sludge. No coolant leaks or vanishing levels in the header tank. It never been overheated. My VIN# is outside of the TSB on the loose steel cups in the rockers.

I am ready to replace the rockers arms as the next step.....or worse.

Thanks
(Cross posted to discoweb also)

 

[David Harris]

How old is the camshaft?

 

[proper4wd]

Slightly increased idle leads me to believe general wear is causing idle oil pressure to be low... possibly leading to lifter noise.

That's where I'd start (checking oil pressure)

 

[XJLI]

my 95 disco "diesels" pretty good. 126k miles on it, fairly good service history (i bought it with 119k). blackstone oil analysis came back with a LOT of copper. motor is otherwise very strong, doesn't burn much, if any oil. i run rotella 15w-40 now, but am doing a change this week to full syn rotella 5w-40. i plan to FIRI til it blows up.

 

[MemphisClassic]

How about exhaust gaskets? Mine 96 devoloped a similar intermitent knock and most engine knocks would be consistent. When you say it happens after warmed up, that is giving the exhaust pipes the chance to heat up and the noise to start. Just my $0.02 worth!

 

[øldabe]

Sounds very much like what's happening with my 4.6. Took it for a drive-by to my local mechanic. He says either a loose cup in the rockers, or a lifter, which is what it sounds like to me.

I did run a quart of atf in the oil which will generally quiet a sticky or collapsed lifter, at least for awhile. No change there. I trust my mechanic when he says that it's a "non-damaging" noise, and to just keep driving it.

it smogs clean, has good compression, and doesn't burn oil.

In my non-professional opinion, your motor sounds good.

 

[David Harris]

Nearing 100,000 the cam is more than ready to be changed. They wear abnormally fast on these engines and then you can do the lifters and refurb the rest of the valve train while your at it. A new cam makes a world of difference and makes the whole engine last longer.