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Modern Engine Blueprinting Techniques: Choosing Valvesprings

by Mike Mavrigian

(Taken from Modern Engine Blueprinting Techniques by Mike Mavrigian) 

Valvesprings control the energy transmitted from the camshaft to the valves. It’s critical to understand the springs’ role and dimensional/clearance concerns.


Valvespring manufacturers apply an antirust coating, which should not be removed. Do not clean new springs with any type of solvent. Handle springs carefully to avoid causing nicks or burrs that could lead to stress riser failure.


When measuring spring load, place the retainer on the base of the spring and note the thickness of the retainer where it makes contact with the outer spring. When measuring installed height, deduct the thickness of the retainer.


Before installing springs, install one valve at a time along with its retainers and locks. Fully pull up the retainer to seat the valve in the closed position. Using calipers, measure the distance from the outside step of the retainer and the spring seat. After measuring and recording each valve’s location, examine the data. The shortest height recorded is the installed height for all springs (spring shims may be used to adjust the remaining valvespring installed heights). Final installed height should be within .020 inch of the specification provided by the cylinder head or camshaft manufacturer.


Before removing the retainers, also measure the distance between the bottom of the retainer to the top of the valveguide seal to verify that the retainer doesn’t contact the top of the seal or guide. Note the maximum valve lift of the camshaft with rocker arms. The distance between the retainer and guide/seal should be at least .090 inch greater than the maximum valve lift. If this clearance is too tight, you may be able to machine the top of the guide to achieve enough clearance.


Inspect for spring coil bind with the springs installed. With the valve in its fully opened position at maximum lift, maintain at least .060 inch. However, depending on the specific type of spring, the recommended minimum clearance may be tighter. Always refer to the spring manufacturer’s specifications. If clearance between coils is too tight, corrective choices include using springs that are rated for greater valve lift, obtaining longer valves, machining spring pockets deeper, or choosing a different spring retainer design.


Be sure to closely inspect for possible contact between the rocker arm and the spring retainer when the valve is in its closed position. If there is a clearance issue, it may be corrected by using a different rocker arm design, or by a combination of different pushrod and valve lengths (shorter valve and longer pushrod).

With dual springs, the inner spring is typically .100 inch shorter than the outer spring. The retainer must be designed with steps to accommodate the inner spring(s). (Photo Courtesy Comp Cams)

 

Installed height is measured from the bottom of the retainer, where the spring makes contact, to the bottom of the spring where it contacts its seat. In the valve-closed position the distance between the bottom of the retainer boss to the top of the valve guide seal must be greater than the max valve lift in order to prevent the retainer from hitting the seal. (Photo Courtesy Comp Cams)

 

 


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