If you’ve purchased an old motorcycle with a stuck engine, it’s not the end of the world. Though, you may be in for a big project.
If you were planning on rebuilding the entire engine anyway, it’s not so bad.
Possible Causes of a Seized Motorcycle Engine
A stuck motorcycle engine can be caused by a number of things, including:
- Seized pistons. If the pistons are melted or rusted, they can fuse to the cylinder walls.
- Seized transmission.
- Stuck clutch.
- Seized starter motor, gears, or starter clutch.
- Broken kickstarter.
- Seized crankshaft or rod bearings.
- Stuck drive chain.
- Stuck brakes.
How to Diagnose a Stuck Motorcycle Engine
If you want to try to avoid tearing apart the engine, you should try to determine what the cause really is.
To check the brakes, chain, and countershaft transmission gears, you can put the engine in neutral and try to push it. If it pushes easily, these are probably not the problem.
To check the kickstarter gear or the electric starter, try to turn the crankshaft by the crankshaft bolt. If it turns, the kickstarter gears or the electric starter motor are likely the issue.
If the pistons or any other internal parts are causing the engine to be stuck, you’re going to need to tear it down.
Before you do take the engine apart, you can attempt to free stuck pistons by dripping penetrating oil down the spark plug holes and letting it soak.
Even if you get the engine free, you should still tear it down. The engine will likely have some damage to the piston rings and cylinder walls. You’ll also want to make sure there are no metal shavings or pieces that have made their way into the crankcases. At a minimum, you’ll probably need new rings and to hone the cylinder bores.
If you begin to disassemble the engine while the pistons are still stuck, you can try to loosen them with penetrating oil and/or heat.