| Diagram | Fig. 1 — CYLINDER HEAD, EXHAUST PIPE · ref 3 |
| Subsystem | engine top |
| Listed in parts books | 1969–1970 |
BSA Exhaust valve lifter
An exhaust valve lifter mechanism (40-0417) used to bleed cylinder compression via the exhaust valve, for easier starting or stopping.
This is an exhaust valve lifter, part number 40-0417, showing up in the catalog under CYLINDER HEAD and EXHAUST PIPE figures. It's the mechanism riders use to lift the exhaust valve off its seat, which lets some compression bleed off the cylinder for easier kickstarting or for stopping the engine without cutting the ignition.
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On a decompressor setup like this, the lifter works through a shaft that runs to the cylinder head, actuated by a lever the rider operates from the bars or the head itself. The catalog record for this part spans 1969 to 1970 model years, but it doesn't tie it to a specific model beyond that, so check it against what's on the bike before ordering.
If you're chasing this part for a decompressor lever or shaft rebuild, it's worth confirming the exact figure your bike's parts book shows, since exhaust lifter mechanisms varied across the engine top end assemblies of this era.
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