Finding the Right Installed Height & Proper Spring Load
In the world of performance engine tuning, valve springs are one of the most critical and overlooked components in your engine. They are selected to complement the system and must be matched with the entire valve train in order for the engine to reach its full potential. The valve spring is basically all that holds the valve train together.
Thanks to the vast array of unique cylinder head options, the days of ordering a valve train "kit” (one deal fits all) are gone. You need to know the dimensions (size) of the spring pockets in your head and how much height you have to work with, in order for the manufacturer to get the valve springs that will work for your application.
Installing a cam that will rpm to 8000 does absolutely no good if you don’t have the correct valve springs. If the valve springs are not designed for the same rpm, the spring load (the force applied by the spring, measured in lbs.) will limit the amount of power the engine makes, or worse, cause severe damage to the engine. Not enough spring load can cause major problems, including premature loss of valve train control (valve float). Too much spring load, however, can wear out flat-tappet cams and prematurely collapse hydraulic lifters (make lifter noise).
1000 lb. Rimac Valve Spring Tester
Use only valve springs that will give the correct spring load with the valve on the seat (seat load) and at maximum lift (open load). The outside diameter of the recommended spring may require that the spring pocket of the head be machined to a bigger size. A spring that is properly contained at the retainer and the cylinder head will offer the longest possible service life.
When installing springs, use COMP Cams® Valve Train Assembly Spray (Part #106) to ease assembly and improve the life of the spring.
COMP Cams® has matched each set of springs for load consistency. A variance of + or - 10% is acceptable for new springs. When checking the spring load on a load tester (Part #5313), measure the thickness of the retainer where the outer spring sits.
Assemble the retainer on the spring and place on the base of the spring tester. Compress the spring to the desired installed height. This is the measurement between the top of the spring (on the bottom side of the retainer) and the surface where the spring rests on the head.
Since the retainer is installed in the spring when checking the spring loads, make certain that the thickness of the retainer is not included when calculating the installed height and is accounted for when compressing the spring. The spring load checker will show to be higher with the spring installed at the correct height.
Too much installed height for a spring will give too soft of spring load, causing valve float and lead to broken parts. Too little height for a spring, will give too much spring load, and may even coil bind the springs, which will break rockers, bend pushrods, etc.
Before installing the spring on the cylinder heads, check the installed spring height (Diagram A).
Finding the Right Height for Optimal Spring Load:
Valve Spring Height Micrometer
1. Install 1 intake and 1 exhaust valve.
2. Get the correct retainer for the spring and correct locks for the retainer. Pull the retainer tightly against the valve locks while holding the valve assembly steady.
3. Place height micrometer (Part #4928 or #4929) or a snap gauge and a pair of calipers on the valve between the spring seat and the outside step of the retainer and turn the height micrometer counterclockwise to establish valve spring height. After you have measured all the valves, find the shortest height. This will become the spring’s installed height on your heads.
4. Add shims until proper height is obtained on the remaining valves.
5. Take the height micrometer and retainer to valve spring tester and check valve spring load at that height.
Before removing the retainers, measure the distance between the bottom of the retainer and the top of the valve seal (Diagram A). This distance must be greater (approx. .045” more) than the lift of the valve. If not, the guide must be machined. This is a very common cause of early camshaft failure.
COMP Cams® # 986-16
Seat Load 132 lbs @ 1.750"
Open Pressure 293 lbs @ 1.250"
Spring rate 322 lbs per inch
Coil bind 1.150
Seat load is with valve seated against the seat @1.75" tall. Open load is with the valve open to 1.250". Spring rate means that for every inch the spring travels, the rate increases 322 lbs. Coil bind means the spring will only compress to 1.150", this means the spring is solid.
Another example, we are going to install this spring on a head. We check our intake spring height, it is 1.810" tall. We would need a shim .060" thick to install @ 1.750".
Next we will check the exhaust. It checks 1.840"; we would need to add a .030” and .060” shim to install correctly.
Once the valve springs have been installed, it is important to check for coil bind. This means that when the valve is fully open, there must be a minimum of .060” clearance between the coils of both the inner and outer springs. If this clearance does not exist, you must change either the retainer or the valve to gain more installed height, or change to a spring that will handle more lift or machine the spring seat for extra depth.
Always check for clearance between the retainer and the inside face of the rocker arm. This will be most evident while the valve is on the seat. Rocker arms are designed to clear specific spring diameters, so you should check to see that you have the proper rocker arm/retainer combination. This situation can also be the result of improper rocker geometry and may be corrected with different length pushrods or a different length valve.
To aid in the engine break-in process, spray the springs, rocker arms and pushrods with COMP Cams® Valve Train Assembly Spray (Part #106).
Check out the COMP Cams® website