The Internal Parts of a 6.5 HP Briggs & Stratton Engine

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The Internal Parts of a 6.5 HP Briggs & Stratton Engine
The 6.5 HP Briggs and Stratton motor powers a push-behind lawnmower's blades. (gazon image by Claudio Calcagno from

Built on the same principles as any gasoline-powered engine, a 6.5 horsepower Briggs and Stratton engine sits atop a push-behind lawnmower in standard applications. Also known as the "Quantum Vertical Engine," you'll find a vertical shaft in this small engine that has a fuel-tank capacity of 1.6 quarts and an electronic ignition for quick starts.

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One Piston

Inside the Quantum 6.5hp engine, one piston powers the motor that turns the mower's blades in a manually operated push-from-behind lawnmower. An engine's heart is its pistons, but in the B&S Quantum engine, you'll only find one piston. The piston sits inside a tube or cylinder inside the engine. A metal ring encircles the piston and provides a seal against the cylinder wall, which creates the compression when the piston moves up and down.

One Crankshaft

In larger engines, multiple pistons attach to the crankshaft via connecting rods and bearings, but in the Briggs and Stratton Quantum engine, the crankshaft only services one piston, with one rod and bearing.

Camshaft and Valves

Two valves--exhaust and intake, depending upon where the piston is in its cycle--pull air in or expel exhaust. The camshaft powers the valves and receives its power from the crankshaft via a gear interface. The Briggs and Stratton 6.5hp engine has an overhead valve set-up, rocker arms, springs, retainers and gaskets.


A flywheel in a car interfaces between the motor's crankshaft, the clutch and the transmission, which turns the wheels as it receives power from the crankshaft. In the case of the 6.5hp Briggs and Stratton motor, the flywheel engages the mower blades, which in turn cuts the lawn.


Though not internal to the engine, the carburettor sits atop the engine and feeds fuel into the insides of the engine's cylinder, which in turn ignites the fuel by a spark from the spark plug, causing a small fuel explosion that powers the piston up and down.

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