Rebuilding the engine of a vintage motorcycle isn't as difficult as you might think. With a proper rebuild kit, which includes all the gaskets you need to complete the job, as well as a thorough engine rebuild manual, you'll be able to tear down and rebuild your Triumph motorcycle's engine without worrying about whether it will ever run again. All too often, people are intimidated by working on their own vehicles when there is really no reason to be afraid.
Drain all of the engine's fluids, including oil and coolant. Please note that early triumphs were generally air-cooled, and as such will not have coolant. New Triumphs, however, are liquid-cooled, and thus will need to have the coolant drained prior to disassembly.
Remove the engine's external components, such as the exhaust headers, spark plug wires and air box. Disconnect the carburettors from the gas tank, then remove any other parts which may impede your progress. If the fuel tank needs to be removed, plug the fuel line and remove the tank to a safe place till it can be reinstalled. You will not have to remove the engine from the motorcycle's chassis.
Begin to disassemble the Triumph engine from top to bottom according to the directions outlined in the Triumph repair manual. It is helpful to use the workbench to lay out the parts of the engine as they are removed from the left side of the bench to the right. This will allow you to later reassemble the engine in exactly the opposite order as it was disassembled. For the time being, retain all the old gaskets.
Remove the old gaskets one at a time from the workbench, replacing them with the new gaskets as the old are thrown away. Depending on the rebuild kit, you may also replace valves, push rods, pistons, piston rings or even the crankshaft. Above all else, keep these parts in the order in which they are laid out on the workbench so that you do not lose track of them or forget to install something along the way.
Refer to the engine rebuild manual, then begin to place the new parts back into the motorcycle's engine one at a time, this time replacing parts from right to left from the workbench. Continuously reference the engine rebuild manual to ensure that parts are being correctly fitted and torqued to the correct specifications. These torque specs will be listed in the engine rebuild manual.
With all parts replaced, reconnect the fuel lines, exhaust headers and air cleaner. Reinstall the fuel tank if you had to remove it.
Refill the crankcase with oil and the radiator with fluid if applicable, then follow the engine rebuild manual's instructions for the initial firing of the engine. The engine is now essentially new, so a breaking-in period is mandatory, just as if the motorcycle were new from the factory. On older motorcycles, this break-in period is particularly critical, as being too hard on a fresh engine can result in power loss or failure of critical components.
Check for coolant or oil leaks immediately following an engine rebuild, and monitor fluid levels for at least a month following.