Just been replacing the timing belt after rebuilding the cylinder head and having problems with the belt moving off the camshaft sprocket. When I turn the engine over by hand to settle the timing/pump belts and to make sure that the timing and belts etc...are running correctly, the timing belt keeps shifting to the left and overhanging the sprocket. The belt also starts to rub on the metal cover plate. Bottom pulley is done up tight, as is the camshaft sprocket. The belt and all tensioners were new 5000 miles ago. There is no play on either pulleys or tensioners. I've taken everything apart several times, but no joy. Has this happened to anyone else, or any ideas on a possible cause? As title says it's a 2.5acv engine.