| Also known as | E4011 |
| Diagram | Fig. 6 — CYLINDER BLOCK AND HEAD · ref 17 |
| Subsystem | engine top |
| Listed in parts books | 1964–1970, 1974 |
Outer valve spring
Outer valve spring for the cylinder head on Triumph 3TA/5TA/T90/T100-family unit twins.
70-4011 is the outer valve spring used in the cylinder head, sitting over the valve stem alongside the inner spring to help control valve closing. It's listed in the parts books under CYLINDER BLOCK AND HEAD figures for the 3TA, 5TA, T90, T100 and related single- and twin-carburetter head variants, so it belongs to that family of unit-construction smaller twins rather than the 650s or 750s.
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The part carries the earlier factory number 99-7036 before Triumph renumbered it, and it also shows up under the E4011 alias, which is the letter-prefix form used in older parts books. If you're cross-checking a set of valve springs against a book from either era, both numbers point at the same physical part.
When you're doing a valve job it's normal practice to replace both inner and outer springs together rather than reusing old ones, since they've usually taken a lot of heat cycles by the time a head comes apart. Bring in your old parts or the book reference for your specific engine if you're unsure which spring belongs where in the stack.
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