astra 2.2 timing chain?

we are doing a job on a vauxhall astra 2.2 petrol engine with a chain, chain snapped bending valves. replaced the valves put engine back together but when doing timing there seems to be slack in the chain enough to skip 1 tooth every few turns of the engine. all tensioners are in properly and tensioned and the chain kit is new, am i missing anything.