| Also known as | M40-0131 |
| Diagram | CYLINDER HEAD, EXHAUST PIPE |
| Subsystem | engine top |
| Listed in parts books | Not catalogued by year yet |
BSA ROCKERBOX STUD C15 B40 - 1/4x26x 2.25 oal
Rockerbox stud for the BSA C15/B40, 1/4 in. x 26 TPI, 2.25 in. overall length.
This is a rockerbox stud, 1/4 inch by 26 TPI, 2.25 inches overall length. The description ties it to the BSA C15 and B40 models, so this is a BSA part, not a Triumph one, despite whatever your parts book heuristics might suggest. It shows up in the cylinder head and exhaust pipe sections of the parts books, which is where you'd expect a stud that secures the rockerbox down onto the head.
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These studs take the clamping load between the rockerbox and cylinder head, so thread condition matters more than it looks like it should - a stretched or corroded stud here can lead to oil seepage or a rockerbox that won't seat evenly. Worth checking the threads in the head casting too when you're replacing one, since a tired stud is often a sign the threads it lives in aren't in great shape either.
The alias forms 40-0131* and M40-0131 refer to the same physical part. If you're working from an older parts book and see one of those numbers, you're looking at this stud.
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