| Diagram | Fig. 5 — CYLINDER BLOCK AND HEAD TR7RV · ref 3 |
| Subsystem | engine top |
| Listed in parts books | 1974, 1976–1980, 1985 |
Cylinder base nut
Cylinder base nut, PN 21-2177, used to secure the cylinder block down to the crankcase.
This is a cylinder base nut, part number 21-2177, used where the cylinder block bolts down to the crankcase. It shows up in the parts-book figures for cylinder block and head assemblies, including the TR7RV, T140V, and T140E, and it also turns up listed under exhaust pipes and silencers figures, which tells you a base stud in this area does double duty holding down exhaust-related hardware on some variants.
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The catalog record runs across model years from 1974 to 1985 and this nut appears in ten separate rows, so it's a part that stuck around through a good stretch of production changes without being redesigned. It's a small, plain-looking fastener but it's doing real work clamping the cylinder base down tight, so it's worth replacing rather than reusing if the old one is worn or rounded off.
If your parts book lists this under a different number, check the catalog appearances above against your bike's figure before ordering, since this nut shows up across several different cylinder block and head listings.
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