Four basic lifter (tappet) types are used in Clevelands: fl at-tappet hydraulic and mechanical, and roller-tappet hydraulic and mechanical. Flat-tappet lifters were original equipment in all 335-series Cleveland engines. Roller tappets were increasingly used in Ford factory V-8 engines after 1985, which is when aftermarket manufacturers began to make them available. More and more engine builds are witnessing the use of roller tappets because there’s less friction, smoother operation, and the ability to run a more aggressive profile without the drawbacks of a radical fl at-tappet camshaft.
Roller tappets are more costly than fl at tappets due to tighter tolerances and a greater number of parts. Their cost puts them outside of the budget-engine category, but they’re worth every penny in what they save in wear and tear. They also give you an advantage if you run a more aggressive camshaft profile.
Although hydraulic lifters saw more widespread use beginning in the 1960s, their use dates back to the 1920s. Hydraulic lifters don’t require periodic adjustment as do mechanical or solid lifters. As the camshaft and valvetrain wear, hydraulic lifters expand with the wear via oil pressure to take up clearance. This keeps operation quiet and reliability sound.
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Hydraulic lifters do well until camlobe and valvestem wear is so excessive the lifter can no longer take up the clearance. Then you hear the telltale “click” or tapping of rocker arm noise, especially when the engine is cold. Sometimes rocker arm click is a faulty lifter (leaking hydraulic pressure) or an excessively worn rocker arm. The first indication of an excessively worn rocker arm is the “clicking” that occurs at any engine temperature. It can also mean oil starvation at the rocker.
Lifter and cam-lobe wear and failure are rarely caused by a manufacturing defect. They fail because you don’t give them a good start when it’s time to fire the engine in the first place. Flat-tappet camshafts must be broken in properly or failure is inevitable. Moly coat must be applied to the cam lobe and lifter face when you’re installing a fl at-tappet camshaft. The engine must be operated at 2,500 rpm for 20 to 30 minutes after the initial fire-up to properly wear in the lobes. Synthetic engine oil should not be used until after the break-in period. During this period, check the pushrods for rotation.
Roller tappets don’t require breakin because rollers and cam lobes enjoy a good relationship to begin with. The lobes are already hardened and the rollers provide a smooth ride. Flat-tappet mechanical camshafts are good for highrevving engines where the inaccuracies of hydraulic camshafts (lifter collapse) are unacceptable. Mechanical camshafts give you accuracy because there’s nothing left to chance. The lift moves with the cam lobe with solid precision. Given proper valve-lash adjustment, mechanical lifters do their job very well. The thing is, mechanical flat and roller tappets have to be adjusted periodically, which can be annoying on a daily driven street engine. This is where you need to do some soul searching before selecting a camshaft.
Written by George Reid and Republished with Permission of CarTech Inc
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