Disassembling an engine can seem a daunting task, especially the first time a mechanic performs this task. But with careful preparation, this is a relatively easy job.
As with many mechanical jobs on a motorcycle, engine disassembly requires advance planning. The novice mechanic will often remove an engine as soon as possible, but this often leads to problems when removing items that have a high torque value such as a clutch retaining nut, for example.
It is, therefore, prudent to disassemble as much as possible of the engine while it is still secured in the frame.
Fluids
Before starting the engine removal process, the mechanic must drain all fluids (engine and gearbox oils). To ensure most of the oils have been drained, it is good practice to do this overnight. Needless to say, the catch-can must be big enough to catch the amount of fluids being drained.
Wherever possible, the following items should (not in any particular order as each engine will differ) be removed or loosened with the engine/gearbox still in the frame:
Gearbox sprocket retaining nut (use the drive chain and rear brake to stop rotation) All external cases (primary drive, ignition hardware etc.) Crankshaft drive gear Cams and cam gear Clutch Stator or generator assembly Carbs Ignition system Oil filter Oil lines Water pipes and pump (where fitted) Hydraulic clutch slave cylinder (where fitted)
Some preparation of the engine in readiness for disassembly is essential if certain settings are not known.
For example valve and ignition timing positions must be noted. All of the various engine settings are in relation to TDC on the compression stroke, it is, therefore, necessary to find this position first. However, if the engine has marks for timing of such items as camshafts, it will be necessary to rotate the engine until these marks align at the TDC point (note camshafts rotate at half the rate of the crankshaft).
Engine Bolts
With all of the above tasks accomplished, the engine retaining bolts can be removed. At this point, it is good practice to protect the frame from scratches by wrapping it with rags or bubble wrap. All the retaining bolts should be backed off before withdrawing them one by one. However, the engine will drop under its own weight at some point so care must be taken not to trap fingers under it. Before removing the engine from the frame completely, it is important to have a place prepared to set it down—a clean bench for example.
With the engine set on a suitable work bench, the remainder of the disassembly process can begin. The mechanic should disassemble as much as possible without removing the barrels and piston. (See warning note below).
Using extractors and/or pullers, the mechanic can remove the drive gears and flywheel easily. Typically most engines locate the drive gears and flywheels with a woodruff key and a tapper. As the pressure needed to break the hold of a tapper is considerable, the mechanic must ensure the pullers are fitted correctly, engaging (where appropriate) any threads to their full extent before applying pressure for removal. In most cases the extractor will require a firm tap with a hammer (see photo) to initiate the extraction process.
Notes
Some shop manuals advise placing a bar through the connecting rod’s small end eye onto the crankcase faces to stop crank movement when removing drive gears or clutch retaining nuts etc. This is very bad practice and can lead to serious damage.
The use of a screw driver to jam rotating gears when attempting to loosen a drive gear must be avoided. The use of special tools (where available) is recommended or, as an alternative, the mechanic can insert a soft material such as aluminum between the teeth.
Further reading
Motorcycle, Engine Disassembly (Bench Work)
Motorcycle Engine Rebuilding, the Basics
As with many mechanical jobs on a motorcycle, engine disassembly requires advance planning. The novice mechanic will often remove an engine as soon as possible, but this often leads to problems when removing items that have a high torque value such as a clutch retaining nut, for example.
It is, therefore, prudent to disassemble as much as possible of the engine while it is still secured in the frame.
Fluids
Before starting the engine removal process, the mechanic must drain all fluids (engine and gearbox oils). To ensure most of the oils have been drained, it is good practice to do this overnight. Needless to say, the catch-can must be big enough to catch the amount of fluids being drained.
Wherever possible, the following items should (not in any particular order as each engine will differ) be removed or loosened with the engine/gearbox still in the frame:
Some preparation of the engine in readiness for disassembly is essential if certain settings are not known.
For example valve and ignition timing positions must be noted. All of the various engine settings are in relation to TDC on the compression stroke, it is, therefore, necessary to find this position first. However, if the engine has marks for timing of such items as camshafts, it will be necessary to rotate the engine until these marks align at the TDC point (note camshafts rotate at half the rate of the crankshaft).
Engine Bolts
With all of the above tasks accomplished, the engine retaining bolts can be removed. At this point, it is good practice to protect the frame from scratches by wrapping it with rags or bubble wrap. All the retaining bolts should be backed off before withdrawing them one by one. However, the engine will drop under its own weight at some point so care must be taken not to trap fingers under it. Before removing the engine from the frame completely, it is important to have a place prepared to set it down—a clean bench for example.
With the engine set on a suitable work bench, the remainder of the disassembly process can begin. The mechanic should disassemble as much as possible without removing the barrels and piston. (See warning note below).
Using extractors and/or pullers, the mechanic can remove the drive gears and flywheel easily. Typically most engines locate the drive gears and flywheels with a woodruff key and a tapper. As the pressure needed to break the hold of a tapper is considerable, the mechanic must ensure the pullers are fitted correctly, engaging (where appropriate) any threads to their full extent before applying pressure for removal. In most cases the extractor will require a firm tap with a hammer (see photo) to initiate the extraction process.
Notes
Some shop manuals advise placing a bar through the connecting rod’s small end eye onto the crankcase faces to stop crank movement when removing drive gears or clutch retaining nuts etc. This is very bad practice and can lead to serious damage.
The use of a screw driver to jam rotating gears when attempting to loosen a drive gear must be avoided. The use of special tools (where available) is recommended or, as an alternative, the mechanic can insert a soft material such as aluminum between the teeth.
Further reading
Motorcycle, Engine Disassembly (Bench Work)
Motorcycle Engine Rebuilding, the Basics
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