Well JACK,s been complaining that his big block 454 engines just not reving to the same peak rpm levels that it used to, so I suggested he come by for a tune-up, during the process I naturally adjusted the valves and during that procedure I leaned on a few valve springs as a un scientific test to see if any felt a bit worn out.
well I found a few that didn,t feel correct so I suggested we test a few and it was obvious that the seat loads varied quite a bit, Keep in mind valve springs are an alloy steel thats been heat treated and the constant flexing tends to rapidly heat the valve springs, that heats counter productive and it will reduce the spring tension. testing has consistently proven at least 40% of the heat a engine produces is related to friction in the valve train.
its fairly common for valve springs to loose 10%-25% of the installed tension loads keeping the valves seated,over time.
this is frequently the reason an engine seems to gradually loose the ability to rev as high as it originally did as a freshly built engine over time, a set of valve springs that were installed height ,at lets say 1.900 inches and 120-140 lbs for a flat tappet cam application, might only test at 90-100 lbs after a year or two of being raced or driven on the street!
This loss of valve spring pressure reduces the engines ability to maintain lifter to cam lobe contact and valve train control.
its not horsepower, its the stress on the valve train, that makes a rocker stud girdle and its increased rigidity useful,
and thats more closely related to average stress levels, RPM and VALVE SPRING LOAD RATES
any time your occasionally exceeding 6000rpm or getting close too 330 lbs of open valve load rate Id strongly suggest screw in rocker studs
any time your intentionally exceeding 6000rpm and exceeding 350 lbs of open valve spring rate a rocker stud girdle might be a good idea.
and if your regularly exceeding 6500rpm and 400 lbs of open valve spring load rate its use is going to become almost mandatory
http://www.summitracing.com/parts/pro-66950
http://www.summitracing.com/parts/sum-141010
additional oil spray directed at the valve springs, thats used to absorb and cool the valve springs will usually add durability and life expectancy to the valve springs
COMP Cams POSTED THESE TIPS
The Truth About Valve Springs
Valve springs are one of the most critical and most overlooked components in your engine. Proper selection of the valve spring begins with identifying the application and selecting all of the valve train components to achieve the engine builders’ goals.
The spring is selected to complement the system and must be matched with the entire valve train in order for the engine to reach its full potential. It does absolutely no good to install a cam that will rpm to 8000 if you do not have the correct springs. Improper selection of the wrong valve spring is one of the most common causes of engine failure. Other common causes are the incorrect installation and improper handling of the valve springs.
Selecting a Spring
1. Use only the valve springs that will give the correct spring pressure with the valve both on the seat and at maximum lift.
2. The outside diameter of the recommended valve spring may require that the spring pocket of the head be machined to a bigger size.
3. One of the easiest and sometimes most costly mistakes made in racing engines is not positively locating the spring. A valve spring that “dances” around on the cylinder head or retainer causes harmful harmonics and excessive wear. A spring that is forced onto a retainer is likely to fail at that coil. That is why we have such a large selection of steel and titanium retainers, hardened steel spring seat cups and I.D. locators to better match our springs. A spring that is contained properly at the retainer and the cylinder head will offer the longest possible service life.
Proper Spring Handling
1. Handle springs with care. Never place in a vise, grab with pliers or hit them with a hammer. This will damage the surface of the spring, which will cause a spring to fail.
2. When separating double or triple springs, use only a durable plastic object that cannot harm the shot-peened surface of the spring. Never use a tool or hard metal object like a screwdriver.
3. Valve springs are shipped with a rust preventative coating that should remain on the spring throughout engine assembly. Do not clean springs with acidic or evaporative cleaners. This causes rapid drying and promotes the formation of rust on the surface, which can cause catastrophic failures. Even a slight amount of corrosion can grow to be a problem.
4. When installing springs, use COMP Cams® Valve Train Assembly Spray (Part #106) to ease assembly and improve the life of the spring.
Checking Loads
1. COMP Cams® has matched each set of springs for load consistency. A variance of + or -10% is acceptable for new springs.
2. When checking the spring loads on a load tester (Part #5313) measure and note the thickness of the retainer where the outer spring sits. Assemble the retainer on the spring and place on the base of the spring checker.
3. 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 where the outer spring sits) and the bottom of the spring on the base.
* NOTE *
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.
Installation
1. Before installing the spring on the cylinder heads, check the installed spring height (Diagram A). This is the distance from the bottom of the retainer to the surface where the spring rests on the head. The valves, retainers and valve locks will be used in this step. First, install the valve in the guide, then install the retainer and valve locks. Pull the retainer tightly against the valve locks while holding the valve assembly steady.
Measure the distance between the spring seat and the outside step of the retainer using your height micrometer (Part #4928 or #4929) or a snap gauge and a pair of calipers. Repeat this procedure for all the valves and record your Information. After you have measured all the valves, find the shortest height. This will become the spring’s installed height on your heads. If your combination includes a dual or triple spring assembly, it will be necessary to allow for the inner steps of the retainer.
2. Once you have determined the shortest installed height, it will be necessary to use shims to obtain this height (±.020” is acceptable) on the remaining valves. These are available through our catalog or at any of
your local COMP Cams® dealers.
3. Before removing the retainers, measure the distance from the bottom of the retainer to the top of the valve seal (Diagram A). This distance must be greater than the lift of the valve. If not, the guide must be machined. This is a very common cause of early camshaft failure.
4. 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.
5. 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.
6. To aid in the engine breaking process, spray the springs, rocker arms and pushrods with COMP Cams® Valve Train Assembly Spray (Part #106).
Breaking In a Spring
1. It is important for new springs to take a heat-set. Never abuse or run the engine at high rpm when the springs are new. Upon initial start-up, limit rpm to 1500 to 2000 until the temperature has reached operating levels. Shut off the engine and allow the springs to cool to room temperature. This usually will eliminate early breakage and prolong spring life. After the spring has been “broken-in”, it is common for it to lose a slight amount of pressure. Once this initial pressure loss occurs, the spring pressure should remain constant unless the engine is abused and the spring becomes overstressed. Then the springs must either be replaced or shimmed to the correct pressure.
inding 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.
IMPORTANT: 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.
EXAMPLE:
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).
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