I have a 95 12v that had the valves adjusted at 80.000 miles the truck now has 198.000 miles do they need to be adjusted again. Was told that they need adjusted at 80 to 100 thousand as this would broken in then and wouldn't need it after that.

 

Hard to say it depends on how hard the engine was run and oil changes .If it was mine I would have them checked.MY.02

 

I think the cummins service manual says to do it every 24,000.

 

AT our work we tried to get people to adjust them every 50K. But I did my old 92 12v and I could not tell any difference ..I think it had about 112000 the 1st time then we did it again at 150k and still I could not tell..

 

We pull a 24 foot enclosed car trailer every summer and change the oil every 3000-3500 miles? total wgt of truck trailer is 15000

 

The first couple of adjustments are the most critical, 24 and 48k.
After that they don't seem to move. I still check every 100k but haven't had to change anything.
If you don't know the truck's long term history, adjust them and you're good for a 100k.

 

I adjusted mine at 235K, 15K after acquiring the truck. I do not know if they've ever been done before, but mine needed it. It's not a big enough job to put off checking.

 

First time I did mine, 245000km, made a huge difference, ran quieter and smoother, and reved up under load a lot nicer.