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Author Topic: Valve Spring Tech Info  (Read 7376 times)
woody
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« on: June 15, 2006, 07:41:57 pm »

Your valve springs and the way they function and fit on your heads can't be stressed enough. They are absolutely vital and if you overlook some things, it may be doomsday for your motor and your bank account.

Valve Spring Pocket Clearance
Valve spring pocket clearance is the gap between the inside diameter
of the valve spring pocket (or cup, if used) and the outside diameter of
the valve spring.



  • Too much clearance will result in the spring "dancing" around in the
    head, which "beats up" the spring mounting surface and the spring
    itself. If this is the case, a spring cup may be used. Additional
    machining of the spring pocket may be required to accept the spring
    cup.
  • Not enough clearance will bind the spring in the pocket,
    overstressing the bottom coil by limiting its movement and not allowing
    the spring to "grow". This will cause the bottom coil to wear against the
    head and/or prematurely fail. Machine the valve pocket using a Spring
    Seat Cutter if not enough clearance exists.

Valve Spring Retainer Fit
The valve spring retainer should fit the valve spring being used. A
slightly snug fit is acceptable, however a fit that is too tight can
overstress the top coil, and cause it to fail. A fit that is too loose can
lead to spring "dancing."

Valve Spring Installed Height
The installed height of the valve spring is the distance between the
valve pocket (or cup, or shims) and the outer edge of the spring
retainer (which is the height of the valve spring) when the valve is
closed. To check installed height, follow the following procedure:
....1. Install the valve in the guide.
....2. Install the retainer and valve locks.
....3. Install all spring cups and/or valve spring shims (basically,
everything except the valve spring).
....4. Hold the valve closed by pulling the retainer up tightly against the
valve locks.
....5. Measure the distance between the outside edge of the valve
spring retainer and the spring seat. A snap gage or a height
micrometer should be used.
....6. Check the distance against what is recommended on the
camshaft specification card. An installed height of +/- 0.020" is
acceptable. ....7. If the installed height is not within 0.020", either
machining the valve pocket, or removal/installation of valve spring
shims is necessary.
....8. Repeat this procedure for the rest of the valves.

Spring Retainer to Valve Seal Clearance

The distance between the innermost step on the valve spring retainer and the valve guide
must be 0.090" larger than the maximum valve lift of the camshaft
Measure the distance between the top of the valve seal to the bottom
of the valve spring retainer. After adding 0.090" to your measurement,
it should still be larger than the maximum valve lift of the camshaft. If
not, machining of the valve guide in necessary for adequate clearance.



Valve Spring Coil Clearance
Coil clearance is the distance between the valve spring coils when the
valve is it maximum lift (fully open). A minimum of 0.060" must exist
between the coils at maximum lift. Coil bind is when the valve spring is
compressed fully-to the point that all of the coils are "stacked up" on
top of each other. A clearance of .100" is recommended for high RPM
applications. Coil bind is a catastrophic condition that will result in valve
train failure.

Disassemble each spring (if multiple springs are employed at each
valve). Check all the springs (both inner, and outer springs) If there is
not 0.060"- 0.100" minimum of clearance between the coils, the
solutions are: the valve retainer, the valve locks, the valve, or the
spring must be changed; the spring pocket must be machined. Keep in
mind that these modifications will change the valve spring installed
height.

Retainer to Rocker Arm Clearance
When installing the rocker arms,
check to see that the inside of the
rocker arms clear the spring
retainers. Many rocker arms have a
"relief" to accommodate large valve
spring retainers.




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