| Also known as | E3966 |
| Diagram | Fig. 3 — CYLINDER BARREL AND HEAD · ref 15 |
| Subsystem | engine top |
| Listed in parts books | 1963–1964 |
Outer, valve spring (red)
Outer valve spring (red-coded), PN 70-3966, used in the cylinder head/barrel assembly to help close the valve.
This is the outer valve spring listed in the catalog under 70-3966, also known by its earlier E3966 number. It shows up in the cylinder barrel and head section of the parts books, where it does the work of closing the valve after the cam and rocker push it open. The catalog marks this one out with a red finish, which is how the factory kept spring rates sorted at a glance when there were multiple springs in the same box.
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On engines using dual valve springs, the outer spring works alongside an inner spring to control valve motion at higher lift and rpm. If you're rebuilding a head and pulling old springs for inspection, it's worth checking free length and looking for any sag or cracking before putting them back in.
Our catalog record ties this part to appearances from 1963 to 1964, but doesn't spell out which specific model it belongs to beyond the cylinder head assembly. Confirm it against your engine before ordering, since spring rates and sizes can differ between years and displacements.
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