Thankfully it's rare that anyone has to pull an engine apart after some catastrophic issue these days. Modern motorcycle engines are generally reliable and hardly ever give major trouble. Routine maintenance and replacing ancillaries should be all that is needed, with valve clearances usually the only time we have to delve inside.
But occasionally something breaks, or hits something else, or wears out and the first we know is a nasty noise, loss of power, a bad smell or – worse – the rear locking up and bits escaping. When this happens, what is the best course of action?
The first step is simple. Diagnosis: see what went wrong and work out if it's something you can repair. If you can peek inside the engine through a hole made where a part escaped, then the whole engine is very likely ruined. Otherwise, does it turn over on the starter? Will it select neutral and change gear if you move the rear wheel? Is there oil and water? It so, is there metal swarf in the oil? Could it be chain, brakes or gearbox? All these questions will help isolate the problem, so that you can then decide if it's economical to fix or replace. Often it will be more economical to replace the entire engine and gearbox than to strip and rebuild. It's also a relatively simple job that can be done without specialist tools. All you need it time – though a strong friend helps, too.
First, all motorcycles are different and there is absolutely no shame in using a manufacturers service manual or an after market technical manual like one from Haynes or Clymer.
Second, if you have decided to replace the engine, make sure that the engine you buy comes with the right paperwork, which includes the motorcycle registration papers (greenbook) of the donor motorcycle. Also if your motorcycle has a chip in the ignition key, you need the ECU and ignition lock from the donor bike. We can only advice the use of the original ECU if the engine from the donor motorcycles is from the same built year...Tag: EngineMaintenanceReplacing-EngineDiagnosisRepairMechanicalTechnicalToolsECURebuild