Shimming Valve Springs

[Daviboy]

Hi guys I just stripped my remaining 5 cylinder heads to check the valves etc. I have noticed that there are 6 shims below each spring seat (1982 Euro SC). I just wondered if this is going to be suitable for my rebuild with 964 profile cams and JE 9.5:1 pistons. I really dont yet understand the reason for shimming unless it is just to increase spring tension? If this is the case and the only reason I would not really want to increase tension that much would I? Engine is going to be re-built for street use only.

[stownsen914]

Shims are used by the factory to adjust tension to keep it within spec for all the valves, given that there is some variation in springs, and probably even in the heads. You can also use shims to increase tension somewhat if needed. If you're going from one stock camshaft profile to another stock profile, I would think you don't need to increase tension.

Scott

[HawgRyder]

If you do play with the shims....be sure to check for coil-bind after the shims are in.
You do not want the lift of the cam to bind the spring in the full open position.
Bob

[lvporschepilot]

+1 for checking coil bind. Make sure you have a .050 buffer in there for max lift to coil bind. You should have no problem if the installed closed seat pressure is factory correct and the springs are in good shape.

[stownsen914]

Coil bind becomes a risk with stock springs as you approach .500" of lift, like on an aggressive race cam. I think the original poster was speaking of switching from one street 911 profile to another, so he probably shouldn't have to worry about that much lift.

Scott