The classic Triumph 650 motorcycle has a four-stroke engine that can be modified to boost horsepower and increase torque. The engine modification adds low-end quickness and raises the top speed of the motorcycle without changing sprockets or transmission gear ratios. You can hop up a 650 Triumph motorcycle by disassembling and assembling the engine in a shop and sending out the cylinders and heads for machine work.
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Things you need
- Standard gauge wrenches and sockets
- Oil drain pan
- Pry bar
- Ring clip tool
- Piston ring compression tool
- Torque wrench
Stabilise the motorcycle on a repair stand. Disconnect the battery leads from the motorcycle battery. Put an oil pan under the engine and remove the crank case drain plug with a box wrench to drain the engine oil. When the oil is drained, replace the drain plug and use a screwdriver to loosen the clamp on the oil line. Remove the line from the oil tank.
Turn off the fuel supply valve under the gas tank. Use a screwdriver to remove the clamp on the fuel hose and remove the hose from the gas tank fitting. Use a socket and ratchet to remove the bolts that hold the gas tank to the frame. Remove the gas tank and set it aside.
Disconnect the throttle cables from the twin carburettors. Remove the air cleaners and use a socket and ratchet to remove the carburettors from the intake manifold on the engine head.
Remove the exhaust headers from the exhaust manifold. Remove the nuts that hold the exhaust pipe to the bike and remove the exhaust system. Disconnect the ignition wires, coil wire and spark plug wires from the engine.
Remove the engine mount bolts from the motorcycle frame. Have an assistant help lift the engine out of the frame and place it on a workbench. Use a socket and ratchet to remove the cylinder heads and rocker arm valve assembly intact. Remove the head bolts and use a pry bar to lift the cylinder heads off the pistons. Lift the cylinders off the crankcase.
Send the cylinder heads and cylinders to an engine machine shop. Have the cylinders bored to the maximum 2.834 inches as specified by the manufacturer. Have the valves reconditioned and have the cylinder heads milled .001 inch. Proceed to the following steps when the parts are returned from the machinist.
Use a ring clip tool and remove the piston pin snap rings from each side of each piston. Use a flat screwdriver and hammer to tap the piston pins out. Remove the pistons from the connecting rod bushings. Install the oversized pistons on the rod bushings and install new pins and snap rings on each piston.
Install new rings on the oversized pistons. Put a new cylinder gasket on the crankcase. Use a ring compression tool and install the milled cylinder head over each piston. Rotate the engine crank with a socket and ratchet to raise one piston fully and insert the ring portion into the cylinder. Attach the ring compressor to the other piston and rotate the crank to insert it into the other cylinder. Press the cylinders down against the crankcase. Use a torque wrench and reattach the cylinder bolts.
Install a new head gasket on top of the cylinders. Place the milled heads and rocker arm valve assembly on the cylinders and torque the heads bolts. Replace the engine in the bike frame and repeat the initial steps in reverse to attach the engine and reassemble the components. Fill the oil tank with new oil.
Tips and warnings
- Refer to a Triumph 650cc repair manual for additional details regarding removal and installation of the engine.
- Upgrade the main carburettor jets for added performance.
- Do not exceed the manufacturer's maximum cylinder bore size.
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