Cummins Valve Lash
I've adjusted a lot of valves but never on a Cummins. The manufacturer recomends adjusting them every 24K miles on the 5.9L 12 valve engine. The valves tend to wear into the head reducing the valve lash. The valve lash takes up the thermal expansion so ideally the lash is 0 when the engine is hot. As the valves wear in and the lash is reduced the valves will not completely close when the engine is hot. This can lead to hard starting when the engine is hot and loss of power. In the long term it can lead to erosion to the valve seats and valves.
The first problem on the Airstream is finding a way to rotate the engine. Cummins designed a handy hole on the transmission mounting flange and a barring gear that slides in. I picked one up at the local Cummins shop for $36. (first Picture) The tool slides into the hole and engauges the ring gear on the flywheel like the starter.
There is a plug in the hole. I was told it was rubber but its actually plastic with an O-ring. Be careful prying it out as you might break the plug like I did. The hole is opposite the starter side of the engine.
Cummins also built a nice plunger on the timing gear case to locate top center on the compression stroke of the number 1 cylinder. It located right under the injector pump. Unfortunatly, the air/power steering pump is located there also. You han not reach it or see it if its even there.
I used the companion cylinder (cylinders that are TDC and the same time)technique. Rotate the engine (normal rotation) and watch the number 6 cylinder lifters. The exhaust closes and the intake starts to open at top dead center. Make a mark on the harmonic ballancer. This is the top of the compression stroke for number 1.
At this point you can adjust half of the valves. Check/adjust intakess 1,2,4 and exhaust 1,3,5. Cummins calls for .010" for the intakes and .020" for the exhaust. This must be done on a cold engine. The book says to let is sit a minimum of 4 hours.
Next rotate the engine 360 degrees based on the mark you made.
Now you can adjust the intakes 3,5,6 and Exhaust 2,4,6.
Torque the adjuster nuts to 18 foot lbs and remember to remove the barring tool before you try to start it. Pretty straight forward.