Art, to answer your question ( sometime between 15,000 and 60,000 miles ) or between
the first and fourth oil change. Note: it spells out very clear to check / adjust and there is
.003 plus or minus window before adjustment is made. If you go Ask Dave, I can provide
hard copy of what is required in addition to checking valves and spec's. Same time checking
valve lash the engine compression brake and electronic injector requires attention.
Dave Atherton Retired Cat Mechanic