Valve lash, for example, is something that should be checked at least every 135,000 miles on a Cummins diesel engine, although many people adjust it even sooner.

The last of the 5.9L 12-valve engines (also known as the 6BT) hit the market in 1998, the same year Cummins released the engine's successor, the 24-valve ISB.

Valve lash, for example, is something that should be checked at least every 135,000 miles on a Cummins diesel engine, although many people adjust it even sooner.

But among Cummins' 1990s offerings, the 12V designation is pretty important, as it refers to the sort of 12-valve engines that tend to rank among the manufacturer's best loved.