| Also known as | AA37, S1865 |
| Diagram | Fig. 2 — CRANKCASE · ref 23 |
| Subsystem | engine bottom |
| Listed in parts books | 1970–1971, 1974, 1976–1980, 1985 |
Cylinder stud
Triumph cylinder base stud, PN 21-1865, secures the cylinder block to the crankcase.
This is a cylinder base stud, PN 21-1865, also cataloged under AA37 and S1865. It shows up in the crankcase figure and does the job of anchoring the cylinder block down onto the crankcase mouth, working with a base nut to hold everything clamped tight against the crankcase.
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The catalog shows this stud appearing across a broad run of years, 1970 through 1985, and it turns up in eight separate catalog listings, so it's a part that stuck around in production for a long stretch without much change. If you're replacing studs on a rebuild, it's worth doing the whole set at once rather than mixing old and new, since they all see the same clamping load and thermal cycling.
Because a stripped or snapped base stud usually means pulling the barrel off to sort it out, it's not a bad idea to check the full set for corrosion or thread damage any time the cylinder comes off for other work. Give us a call if you want to confirm which stud positions on your engine take this particular length before you order.
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