| Also known as | E3668 |
| Diagram | Fig. 6 — TIMING COVER, CONTACT BREAKER AND COILS · ref 9 |
| Subsystem | engine top |
| Listed in parts books | 1963–1970 |
Screw (0.625 in. U.H.)
A 0.625 in. U.H. screw used across cylinder head, chaincase, timing cover, and gearbox cover assemblies on several Triumph unit twins.
Screw, 0.625 in. U.H., part number 70-3668, also listed as 9998-412 and E3668 in older books. This is a small fastener that turns up across a lot of different assemblies rather than one specific spot on the motor - the catalog shows it used on cylinder block and head jobs for the 3TA, T90, T100S, T100C, T100R, and T100T, as well as on chaincase and chain covers, timing covers, contact breaker housings, and gearbox outer covers.
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Because it shows up in so many different figures, this is one of those small screws that Triumph used wherever a 0.625 in. U.H. length fastener was called for, rather than being unique to one job. If you're chasing one down for a specific cover or housing, it helps to have the parts book open to the exact figure so you know you're pulling the right length.
Given how many places this one fits across the mid-to-late 60s catalog runs, it's a good one to keep a few of in a drawer, since covers and housings on these engines use several similar-looking screws and it's easy to grab the wrong one.
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