Valve Springs

[akadeutsch]

When I set out to find valve springs I could not find a descent article that put everything in one place. So that is what I've tried to do here.

Probably the most important factors in selecting valve springs are coil bind height, correct seat pressure, and correct open pressure for the camshaft you are using. We must also note the physical dimensions of the spring to insure that they fit into our chosen cylinder head.

Springs not only come in different lengths and pressures they also come in different diameters. Generally speaking when you increase the spring pressure you will also increase the diameter of the valve spring itself. The cylinder head you are putting these springs into may not be machined for this diameter so you will need to machine the spring seat to accommodate the larger spring if you wish to increase seat/open pressure.

Coil bind refers to the distance the spring can be compressed before the coils come into contact with one another. When the valve spring is compressed until its coils touch one another and can travel no further, it is said to be in coil bind. To measure this you must install the retainer in the valve spring, then compress the spring until it coil binds; Now measure from the bottom side of the retainer to the bottom of the spring. This measurement is the coil bind height. This can be done on the cylinder head with a spring compression tool, in a bench vise, or in a professional valve spring tester.

Now, subtract the coil bind height from the valve spring installed height. The difference is the maximum spring travel. Spring travel must always be at least .060" greater than the full lift of the valve. This safety margin of .060" (or more) is necessary to avoid the dangers of coil bind and over-stressing the spring. If coil bind occurs, the resulting mechanical interference will severely damage the camshaft and valve train components and could cause catastrophic engine damage.

Spring pressure is also one of the key factors in determining which spring should be used for which application. Use only valve springs that will give the correct spring pressure with the valve both on the seat (open) and at maximum lift (closed). Seat pressure also keeps the valves from bouncing on their seat. If the valve bounces, cylinder pressure (power) is lost. Repeated bouncing of the valve is like a Jack hammering action, and can result in the head of the valve deforming or ("tuliping") or actually breaking from the valve stem resulting in catastrophic engine failure.

When choosing a valve spring start with your chosen cam manufacturer. They will be able to give you spring rate and lift values for your chosen cam shaft…and can probably recommend the right spring. Then look at your head or get your OE spring dimensions and make sure that your springs will fit into their seats.

Am I missing anything?

[GP Jeeper]

Akadeutsch,

Great posting. This is some of the fundamental, basic info needed to clarify (de-mystify) key aspects of home building a Jeep Stroker. I am planning my first Jeep stroker and am trying to gather as much info as possible before jumping in, so this article is much appreciated. I am currently in Afganistan so at this time planning, reading, learning, dreaming is all I can do...
When I get home, the patient will be a 2004 Jeep Grand Cherokee Freedom Edition. Plans are: Mild lift, 31-33" tires, larger wheel wells via Bushwacker flares, custom front bumper/winch, and STROKER 4.6L!
It will be used mostly for daily driver, towing, and deerslaying trips to Michigan's northwoods.
Thanks for the info.