gu 2001 4.2t engine tapp

If it sounds like tappet noise it probably is. You may have wear on the face of the rocker which contacts the valve stem. If this is so and you are setting the valve clearences with a feeler strip it will result in a wider clearence than you are measuring. the wear will be at the contact area of the face only and the feeler strip will be accross the top of the valve stem and the unworn part of the face of the rocker, effectively adding the wear to the gap you are measuring. If this is the case you will either have to have the rockers faced or cheat and set them with a dial guage. Hope this helps.

I had a petrol patrol block the feed oil gallery which starved the top for lubrication. The first result was wear in the rocker shafts. Remove valve cover and run to check for oil feed. It won't make too much of a mess. Check for shaft to rocker clearance on the valves which are opposite to the ones you have set on rocking.

Hi are the tappets being set in the correct sequence, the Nissan sequence is a bit different to a lot of other makers
ray

Gday Brenn dog,
procedure for valve clearances is:


No1 TDC set 1,2,4,5,8,9
No6 TDC set 3,6,7,10,11,12 all set to 14 thou HOT setting


Regards
Sevo

Ave a look at the injector pump.. Have heard of this exact noise being from the pump...

Brenn dog,

It is common on that engine, mine did the same, it dissapeared when the injectors were done, it is a knocking noise which accentuates at idle, although mine dissapeared now, it still does it every now and then, it just comes and goes, the diesel specialist said that they did several tests over the years and it is related to the chamber temperatures.
IN mine the noise was there from brand new, I have heard a whole heap of 4.2s with the same noise now..

Mine was very noticeable on very cold temperatures.

Will