🛠️ Why Your MGB Has a "Slow Crank When Hot" (And How to Fix It)
That painful, slow cranking on a hot MGB engine is a classic symptom of starter heat soak. Because the original Lucas starter sits directly underneath the exhaust manifold, it bakes in engine bay heat after a long drive.
Here is exactly what is happening mechanically:
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The Physics of Heat Soak: As the temperature rises inside the original starter, the electrical resistance in its copper windings increases dramatically. This resistance acts like a bottleneck, choking off the battery current (amperage). Even with a brand-new battery, the starter simply cannot get enough electrical juice to spin the engine at normal speed.
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The "Click but No Crank" Bonus: If it gets hot enough, the voltage drop becomes so severe that the heavy, original bulkhead solenoid won't even fully engage, resulting in that infamous, frustrating metallic click.
The Solution: Modern Gear-Reduction Technology
The permanent fix isn't a bigger battery; it's potentially swapping the heavy, original Lucas unit for a modern high-torque gear-reduction starter.
These units solve the heat problem in three ways:
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Half the Amperage Draw: They use modern electrical architecture that requires roughly 50% less current from the battery to turn the engine over.
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Mechanical Leverage: Instead of relying purely on brute electrical force, they use an internal gear reduction ratio (usually around 4.4:1) to mechanically multiply torque. Even if the engine is hot and tight, the gears give it the leverage it needs to spin effortlessly.
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Aluminum Heat Dissipation: Unlike the heavy cast-iron original housings that trap heat, modern units use aluminum casings that dissipate heat quickly.
