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Valvetrain Service and Adjustment

Valvetrain Service and Adjustment. Camshaft R&R, Valve Adjustment, Valvetrain Geometry Check, Camshaft Degreeing, Valve to Piston Clearance Check. Camshaft R&R. Many vehicles can have the cam replaced “in-chassis.”

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Valvetrain Service and Adjustment

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  1. Valvetrain Service and Adjustment Camshaft R&R, Valve Adjustment, Valvetrain Geometry Check, Camshaft Degreeing, Valve to Piston Clearance Check

  2. Camshaft R&R • Many vehicles can have the cam replaced “in-chassis.” • If a cam lobe goes flat the metal may have embedded itself on the cylinder walls; The chilled iron will seriously score cylinders. • When replacing a cam “in chassis” use a cam handle to remove the cam without damaging the bearings. • If a cam handle isn’t available, one can often be made by welding a length of pipe to the old timing gear.

  3. Camshaft R&R • NEVER use used lifters on a new cam. They develop a wear pattern and if used a new cam they will prematurely wear the cam. • New lifters may be used on a used cam. • Always use a quality cam break in lube. • When breaking the cam in, follow the cam manufacturers procedures (2000 RPM for 30 min).

  4. Valve Adjustment • Be aware of whether the valvetrain needs “lash” or “pre-load” • DO NOT adjust valves with engine running • Use manufacturer’s procedure if using stock camshaft • The following procedure will work on any engine regardless of cam design • Turn engine over by hand; When exhaust valve starts to open, adjust the intake valve. When the intake valve starts to close, adjust exhaust valve

  5. Valve Adjustment • If the cylinder head or block was machined, or non-stock valvetrain components are used on an engine with non-adjustable valvetrain, lifter pre-load should be checked. If no specifications are available from either OEM or aftermarket lifter manufacturer pre-load the lifter .030.” ( .010”) • If the valvetrain is non-adjustable, shims may be used under the rocker arm studs/bolts to raise or lower rocker arm. • The valvetrain may also be able to be converted from non-adjustable to adjustable by using locking type nuts or poly-locks (different studs may also be needed).

  6. Valvetrain Geometry Check • Whenever significant (more than .005”) machining has been done to either the head or deck, or non-stock valvetrain components are used; Valvetrain geometry should be checked. • Areas that should be checked are: • Rocker arm to valve spring/retainer clearance. • Rocker arm to rocker arm stud interference. • Proper rocker arm to valve tip contact. • Pushrod to cylinder head/guide plate interference. • Valve retainer to valve seal clearance. • Coil bind.

  7. Rocker Arm to Valve Spring/Retainer Clearance • Check for interference on the side of the spring as well as on the top • Check through the entire range of valvetrain motion

  8. Rocker Arm Stud to Rocker Arm Interference • Check that the slot is long enough to clear stud at max valve lift (min .050”)

  9. Proper Rocker Arm to Valve Tip Contact • Rocker arm moves across the valve tip as valve opens because rocker arm moves in an arc while valve moves straight up and down • At mid-lift valve should be at centerline of valve tip and at no point in the range of motion should be more than .080” from centerline • Different length pushrods will adjust contact pattern Ideal Contact Pattern

  10. Pushrod to Cylinder Head/Guideplate Interference • Check for interference between pushrod hole in head and pushrod through full range of valve motion • Check for interference between guideplate and pushrod through full range of valve motion

  11. Valve Retainer to Valve Seal Clearance • Check clearance between PC seal and retainer at full valve lift (min .050”) • With spring removed and retainer installed, use a dial indicator to move valve to max lift, then measure clearance

  12. Coil Bind • At max lift you must have a minimum of .040” between the coils of the valve spring • Subtract valve lift from valve spring installed height to find the height of the valve spring at max lift. Compress the spring to this height in the valve spring tester and measure the distance between the coils with a feeler gauge

  13. Camshaft Degreeing • Degreeing a camshaft ensure that the camshaft was ground correctly and that the cam drive is marked accurately. • Cam degreeing is advised but not mandatory on stock rebuilds. • If cam timing needs adjustment, adjustments can be made with multiple keyway gear sets or offset cam dowel bushings.

  14. Cam Degreeing • There are two methods generally used to degree a camshaft • Intake lobe centerline method • The intake lobe centerline (degrees ATDC that the intake is at max lift) is determined and compared with the cam card • Valve opening method • The valve opening points are determined and compared with the cam card • This method is also useful for finding the measurements of an unknown camshaft

  15. Valve to Piston Clearance Check • Valve to piston clearance is critical and must be checked on any engine built using non-stock camshafts or that have had significant (more that .005”) machining done to the heads or deck surface • Valve to piston clearance is the lowest between 15 BTDC and 15 ATDC • Check valve to piston clearance at 5 degree intervals

  16. Valve to Piston Clearance Check • Insufficient valve to piston clearance can be corrected by flycutting the pistons (machining the valve reliefs deeper) • Use a dial indicator and checking springs to measure valve to piston clearance • 1. With cam degree wheel still attached to engine, set cylinder head (with checking springs installed in #1 cylinder) on engine • 2. Mount dial indicator so indicator rides on the valve tip and is parallel with valve travel • 3. Turn the engine over until it is at 15 degrees BTDC • 4. Push the valve down until it contact the piston, read the valve travel with the dial indicator • 5. Add the thickness of the head gasket, subtract the valve lift, and compensate for any deck clearance variations (this is the valve to piston clearance) • 6. Minimum clearance IN - .100” EX - .120”

  17. Piston to Head Clearance • Piston to head clearance must be a minimum of .030” • On wedge type heads piston to head clearance should ideally be between .035” and .050” • This optimizes squish and quench • On wedge type cylinder heads with flat or dish pistons, piston to head clearance is the thickness of the head gasket plus the deck clearance • On other engine types install the cylinder head on the engine without a gasket and put a small ball of play-dough on the piston top. Rotate the engine one revolution and the remove the head and measure the thickness of the play-dough

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