The problem is not usually the chain, but the chain guides. Especially the ones on the left side (Drivers side here in the US). The guides get old and break. A piece of the guide falls down and jams the chain. The cam gets out of time and it bends or brakes the exhaust valves in the left head. You are looking at 3 to 4 grand to fix it correctly. A new chain and upper guides will prevent this and will only cost a few hundred. At this point, the valve covers need to be removed, the cam timing checked and the guides checked for wear. Also, check the color of the guides. If they are white or lite tan than they have already Been done. If they are dark brown than replace them before the engine is started again. There has been a lot of old 126's junked because the plastic guide broke.

Paul

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84 500 SEL (307,xxx miles)