OHV valvetrains are the most complex, with lifters that ride on the camshaft lobes, pushrods that transfer motion up to the cylinder head, and rocker arms that pivot on shafts or studs in response to the pushrods and actuate the valves. OHC valvetrains can vary from the pivoting rocker type followers ordinarily used with SOHC (Single OHC) engines, to the simple buckets between the cam and valves common to DOHC (Double OHC) designs.

Reducing internal engine friction helps parts last longer and improves engine efficiency, for greater power and fuel mileage. To that end the lifters and cam followers in most modern engines have rollers that ride on the camshaft lobes instead of flat surfaces. Along with reducing friction, roller lifters also can be used with more aggressive cam lobe profiles that allow the valves to be opened faster. Unlike flat tappet cams, they can also be reused with a new cam. Flat tappet lifters develop specific wear patterns on the lobes, and must be replaced when a new cam is installed.

Valvetrain problems are often caused by excessive clearance. As cam lobes, lifters/followers, pushrods, and rocker arms wear, clearance is increased. Once clearance starts to increase, the pounding experienced by each component becomes greater as the lash opens and is taken up during valve operation. This can result in bent pushrods and broken rocker arms. Clicking noise in the valvetrain area can indicate excessive clearance, which can often be confirmed with a visual inspection. Check pushrods for a bent condition by rolling them on a flat surface. Inspect rocker arms for wear at the pivot and valve contact areas.

The valvetrain converts the rotating eccentric motion of the camshaft lobes to the reciprocating motion of the valves. Valvetrain design and componentry differs according to where the camshaft is located. On Over Head Valve (OHV) engines the camshaft is mounted in the cylinder block. On Over Head Cam (OHC) engines one or two camshafts are mounted on the cylinder head. Whatever the configuration, we have the replacement parts for a successful repair.

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As the engine runs and parts expand from heat, valvetrain clearances can change. There are hydraulic valvetrains with mechanisms to compensate for these changes, and mechanical valvetrains that have a specified clearance, or lash, that ensures the valves can fully close. OHV valvetrains have hydraulic lifters while OHC valvetrains have hydraulic lash adjusters. The plungers, check valves and springs in these devices are supplied with pressurized oil from the pump and maintain zero lash in the valvetrain. The clearance in mechanical valvetrains must be checked periodically and provisions for adjustment are included.

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