Mark Houlahan
Tech Editor, Mustang Monthly
September 11, 2013

We've seen factory hydraulic roller cam engines easily surpass 100,000 miles of use, and even our own 347 stroker with stout hydraulic roller cam, double springs, and roller rockers made it to 118,000 miles of daily beatings before a lifter failure took out a few cam lobes. It is common to pull a hydraulic roller cam out of an engine for an upgrade and see little to no wear on the lobes due to the roller cam's low-friction roller tappets. Even OE shop manuals state that roller tappets can be reused with a new cam and maintaining lifter-to-cam lobe pairing isn't critical like it is with a hydraulic flat-tappet cam where the lifter base and cam lobe wear together in a marriage of sorts. Of course, this is all only possible with a thorough inspection and finding the used lifters in sound order. Any question and you should replace the lifters when swapping from one roller cam to another—stock replacements are dirt cheap at about $100 a set.

Your typical street engine sees valvetrain loads in excess of 1,500 pounds per square inch as the valvetrain is compressed by the lift of the cam lobes. These loads are actually higher than the buckling load of your standard 5⁄16-inch hollow pushrod. However, the load is applied and released so quickly that the pushrod does not have time to buckle from the pressure! A flat-tappet cam tends to have higher acceleration rates to make up for some of the limited velocity and lift that is inherent to the cam design. This, in turn means, just as high, if not higher, loads as a roller cam profile. Interestingly, most people associate high spring loads as the main contributor to valvetrain stress and failure, when in fact the valve mass, rpm of the valvetrain, and profile acceleration rates are much more critical to valvetrain stress and associated failures, Billy explained to us.

Arguably one of the worst "cons" to retrofitting a roller cam to a classic Ford engine setup is the cost; especially if you are using a retrofit kit of matched parts with link-bar style lifters. You'll spend anywhere from $700 to well over $1,200 depending upon cam grind, type of roller lifter, roller retrofit hardware, valvesprings, pushrods, and so forth. Meanwhile a traditional flat-tappet camshaft and matched lifter/spring/timing set kit is roughly going to set you back around $450. So you can see how just shopping by price makes a roller cam conversion a bit of a bitter pill to swallow. However, spending that extra money up front (especially if you're building a complete engine) is cheap insurance, as there are thousands of horror stories across the Internet of brand-new engine builds and crate engines not making it through their flat-tappet cam break in, and taking bearings and other hardware with it during the failure.

16. Once the solid or modified lifters are installed, assemble the rest of the valvetrain on that one cylinder and set the valve lash to zero. Essentially, you want to adjust the rocker until there is a slight drag on the pushrod (spin it with your fingers as you tighten the rocker arm)—you don’t want to pre-load the valve spring. You can then continue with standard piston-to-valve clearance checking steps.

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19b. We’ll close with one last word on flat-tappet cams. If you must run a flat-tappet cam (original 289 Hi-Po, race class rules, and so on), Comp Cams offers the ability to have any of its flat-tappet cams (hydraulic or solid) run through the company’s new in-house Pro-Plasma Nitriding service. This industry exclusive machine uses a patented pulsed nitrogen plasma process to infuse nitrogen ions into the cam, strengthening and hardening the metal surface on a molecular level.

Gears of Change

One of the most confusing aspects of converting to a roller cam in an early non-roller application is that of the distributor gear material, and what material is compatible with what cam. More confusion ensues when you consider that even within one manufacturer (like Comp Cams), there can be several different cam gear requirements depending upon the roller cam line being discussed. For OE-type camshafts, the roller cam is high-grade steel, sometimes billet, and that includes the cam gear. Ford, in turn, used a treated steel distributor gear. This offers the best life and wear and is compatible with many aftermarket roller cams as well. It is imperative that you know what your aftermarket roller cam material is and if the gear itself is the same material. Some cams utilize a pressed on gear to allow compatibility with flat-tappet iron distributor gears while others, like Comp Cams, use a ductile-iron cam core that is austempered on the lobes to harden just the lobes for the roller tappets, leaving the cam gear area as the standard ductile iron and compatible with iron gears. These cam cores are called Selective Austempered Ductile Iron (SADI) and are denoted by the "-8" on the end of their part numbers.

For the longest time, the sacrificial bronze distributor gear was considered the answer for roller cam use. This may have been fine for a weekend race car that gets constant tear downs and inspections, but for a street driven car, it can quickly become a nuisance. Worse yet is using too hard of a distributor gear and destroying the gear on the camshaft. Besides bronze gears and the stock treated steel gear from Ford, you'll find additional options such as aftermarket steel gears and even polymer gears. When purchasing a new roller cam, the cam manufacturer can point you in the right direction for the proper matching gear, or they can tell you if the gear you have now on your distributor is compatible. Ensuring you have the right hardware means a long life for your camshaft and your distributor.