Mechanic Warns 2019+ 6.7L Cummins Owners of “Number One Problem” That “You Cannot Avoid”Dave from Dave's Premium Engines isn't afraid to tell it straight. Working through three fifth-generation 6.7L Cummins blocks in his engine machining shop alongside technicians Jake and JJ, he landed on a verdict that owners of 2019-and-newer Ram 2500s and 3500s need to hear: the factory valvetrain is a ticking clock, and unlike some of the other failure modes he pulled apart on camera, this one isn't conditional."This is the number one problem in the 6.7 Cummins," Dave said. "I tear down these – this is the one that you can't avoid. You cannot avoid it, okay?"Why the Fifth-Gen Valvetrain Is a Problem From Day OneEvery Cummins-powered Ram from 1989 through 2018 ran a flat-tappet valvetrain that required periodic valve lash adjustment – and earned a long reputation for durability. In 2019, that arrangement gave way to self-adjusting hydraulic roller lifters, which eliminated the maintenance interval and quieted the top end.AdvertisementAdvertisementIt sounded like progress. It wasn't.The core issue isn't the switch to hydraulic lifters in principle. It's more about the specific design of the hydraulic lifters Cummins chose. Among several red flags, the rollers lack needle bearings. Compare that to Ford's Power Stroke units, which do have them.Dave's teardown made the mechanical failure sequence visual. A roller lifter is precision-dependent: it must travel straight up and down in its bore. When the bore has excessive clearance, the lifter starts rocking sideways with every cam rotation. That side-to-side movement creates fretting on both the roller and the cam lobe, accelerating wear that eventually scatters metal throughout the engine.When a roller seizes and stops rotating entirely, it drags across the cam lobe, destroying it and sending debris through the whole oiling system. That contamination circulates to bearings, oil galleries, and every surface the oil reaches.AdvertisementAdvertisementThe pushrod and rocker arm side of the equation is equally compromised. Dave held a first-through-fourth-generation pushrod assembly next to a fifth-gen unit and pointed out what changed: the older design had a small oil reservoir at the cup that kept lubricant at the rocker contact point even after a cold overnight sit. The new design drains dry. Every morning startup is effectively metal-on-metal until oil pressure reaches the top end. The worn rocker arms and pushrods Dave pulled from all three blocks reflected exactly that – pitted contact surfaces and metal degrading in real time, with nowhere for that material to go except back into the circulating oil.In some fifth-gen engines, lifter noise begins within the first 10,000 miles. Making it past 100,000 miles without a problem is considered a high-mileage result. That's a far cry from the durability every earlier Cummins generation delivered.What makes this particular failure mode stand apart from the injector and piston damage Dave also uncovered in the video is its inevitability. A runaway injector can be caught early with an exhaust pyrometer. Maintenance neglect – thick sludge caked across the entire valvetrain deck of one of the three blocks – is a choice. The roller lifter geometry issue is factory-built into every 2019-and-up engine. You can do everything right and still be working against the clock.The Fix Involves Going BackwardHamilton Cams' flat-tappet conversion kit reverts the late-model 6.7L back to the proven arrangement that was standard for 30 years.AdvertisementAdvertisementThe all-inclusive kit pairs DLC-coated tappets with Hamilton's 178/208 efficiency camshaft, upgraded pushrods, and adjustable rocker arms fitted with DLC-coated trunnions and improved oiling passages, giving the contact surfaces both lower friction and better lubrication.Dave unboxed a complete kit on camera and confirmed his shop stocks around 30 of them. The first instruction in the kit paperwork, as Dave noted with a laugh, is "Pull Cab." This isn't a shade-tree job. Getting at the rear cylinders properly means lifting the cab off the frame, which is why Dave's shop ships completed trucks back across the country after doing the work in Utah.Failure typically announces itself as ticking, misfires, rough running, or metal contamination found in the oil. Left unaddressed, the damage can escalate to a full engine replacement.Worst-case repair bills for 2019-and-up Ram owners have reached $25,000 and beyond. The 6.7L Cummins is a great engine – except for this generation's valvetrain. Take care of it and it'll take care of you. But with this particular design flaw, "taking care of it" means dealing with a problem that Cummins built in from the factory.