Setting Valve Spring Heights

By Greg Rollin

 As noted in Setting Stem Heights, when grinding the valve seat and valve face, the valve spring installed height will be increased a corresponding amount. The use of different retainers/rotators as well as valves with different keeper heights will also effect the valve spring installed height. For maximum performance, valve spring installed heights must be set to the manufactures specifications. Valve springs are designed to provide a specified pressure at a given installed height. When this height is altered due to the valve grinding process, the springs will no longer provide the proper tension. Thus limiting the engine rpm capability. It is also important to use valve springs that match the camshaft profile.

 

 

 After all machining has been performed on the valve seats and valve faces, measure the distance between the spring seat and retainer (or rotator). Compare this number to the manufactures installed height specification.

 

To compensate for the increased retainer height after valve and seat grinding, the proper spring installed height can be achieved with the use of shims. By placing the appropriate thickness shim(s) on the spring seat, the spring installed height can be restored. We offer a valve spring shim kit (Part Number 14-268) that contains 16 of each .015", .030" and .060" thickness shims. The proper spring installed height for most Oldsmobile applications is 1.670". Springs should never be shimmed beyond the installed height. And shims should never be used as an attempt to compensate for worn springs.

 

 

 In addition to installed height, valve springs must be checked to insure they are within manufactures specifications at open and closed rates. A spring showing a load loss of 15 lbs. or more from either specification will need to be replaced.

 

MISCELANIOUS SPRING NOTES

When installing camshafts with over .500" valve lift, several clearances will need to be checked and corrected if needed.

 

 

At full valve lift, there needs to be a minimum of .090" between the bottom of the valve retainer/rotator and the valve stem seal. This may require machining the top of the valve guide as shown above. Using this type of cutter also machines the guide for the use of a positive style valve stem seal. Which is required when using dual valve springs. We recommend using Sealed Pro #ST-2001 or ST-2003 valve stem seal for these applications.

When using valve springs matched to the camshaft, assembled at the proper installed height, coil bind should not be a problem. However it is always advisable to check. By placing the spring in a tester as shown above or a thick jawed vice, compress the spring to the installed height. Then further compress to the maximum valve lift. There should be a minimum of .050" between the coils of the spring.

 

  

SHALLOW OR DEEP SPRING SEATS?

Heads that were factory equipped with valve rotators will have .125" deeper spring seats than those that use solid retainers (see chart below). In performance and race applications, the (heavy) rotators should be replaced with solid retainers. Many aftermarket cam companies offer different solid retainers that will compensate for the .125" difference in installed height (or allow the use of taller springs). For street and street performance applications, originally equipped with rotators, we recommend using them. By turning the valve two degrees per cycle, the rotators virtually eliminate any carbon buildup on the valve seats and valve faces. Thereby increasing the life of the valves and seats as well as maintaining compression. Oldsmobile engineers found in a wide open engine test for 1300 miles at the equivalent of 130 mph, the performance loss was 50 percent without the rotators and only 9 percent with the rotators! This more than makes up for the extra weight of the rotators over lighter retainers in a real world street application.

 

REFERENCE CHART

SHALLOW

All 1964-1967 330. Casting code 1, 2, 3 and 4.

All 1968-1969 350. Casting code 5.

All 1965-1969 400 and 455. Casting code A, B, C and D.

DEEP

All 1970 350. Casting code 6.

1971 350. Casting code 7. Note: some #7 heads utilized different combinations of retainers/rotators. Resulting in stepped spring seats.

All 1972-1976 350. Casting codes 7A and 8.

All 1970 455. Casting codes E and F.

All 1971 455. Casting code H

1971 455. Casting code G. Note: some G heads utilized different combinations of retainers/rotators. Resulting in stepped spring seats.

All 1972-1976 455. Casting codes GA, J and KA.

If you are still unsure if your heads have deep or shallow spring seats, measure from the rocker arm boss to the outside (exhaust) edge of the spring seat. Shallow seats will measure at approximately .640", deep spring seats will be approximately .765".

  

 

VALVE SPRINGS AND PARTS

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COPYRIGHT © 2002 Greg Rollin/Supercars Unlimited. Any reproduction of the text and/or images strictly prohibited. All rights reserved.