* Valve damage: The most common consequence of a broken timing belt in an interference engine (like many 1.2L Renault engines) is bent valves or even piston-to-valve contact. When the belt breaks, the valves and pistons can collide, causing significant damage.
* Other internal damage: Besides valves, other components could be damaged, including:
* Piston damage: Holes, cracks, or other damage.
* Connecting rods: Bending or breaking.
* Crankshaft: Damage is less common but possible.
* Incorrect timing (despite checking): While you say the timing is set, there's a small chance of a slight misalignment or error in the process. Double-checking is crucial. A single tooth off can cause significant running problems.
* Other issues unrelated to the belt break: Although less likely given the timing belt failure, other issues *could* contribute to rough running, such as:
* Spark plugs: Worn, fouled, or incorrectly gapped.
* Ignition system: Problems with the coil, wires, or distributor (if applicable).
* Fuel system: Issues with injectors, fuel pressure, or the fuel pump.
What to do:
1. Re-check the timing: Even if you're confident, meticulously verify the timing marks again.
2. Compression test: This is the most crucial step. A compression test will reveal if any cylinders have low compression, indicating valve or piston damage.
3. Inspect the spark plugs: Examine them for fouling, damage, or abnormal wear.
4. Diagnose the ignition system: Check for spark at each cylinder using a spark tester.
5. Check for fault codes: Use a diagnostic tool (OBD reader) to check for any stored error codes.
If the compression test reveals low compression in one or more cylinders, it's very likely there's internal engine damage. This will likely require a more significant repair, potentially involving head gasket replacement, valve adjustment, or even a head rebuild or engine replacement. Ignoring this could lead to further, more costly damage.
