just got the son a nold 84 300sd and it has a knocking in thr valve cover area up front . well 300.000 miles i thouthe valve adj. pulled the cover and checked them and all were fine . started it up and there was no noise. looked in the valve cover and there was chain marks . installed new chain ,and only dropped it in the front cover once .fished it out with a magnet and luckily it didnt jump off of the pump. reinstalled the covet and it seems to be knocking again . any ideas

Maybe the chain guide rail or tensioner are loose/worn out, that might make that sound like that ........thats just a guess though.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I would have replaced the guides/tensioner too...

when they break off is what usual causes the timeing chain to break.....or so I gather from reading this board.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Check the vacuum pump while you're in there. That is a common source for knocking in that area. Because a vacuum pump can disintegrate and wreck you engine, it may be best to pull it to make it absolutely certain that it is not busted before moving on.