Over the years I`ve worked on everthing from chainsaws to Caterpillar tractors. I like to consider myself a somewhat sophisticated driveway mech, but I`m just about licked by a `92 Nissan Sentra! In the course of replacing a cracked cylinder head, I did the cam chains, guides, tensioners, etc. Studied the manuals and aligned all the timing marks. The mistake I made was in not installing the lower cam chain tensioner before rotating the engine to double check my marks. I think the lower chain jumped a tooth and the marks haven`t lined up since. The valves don`t contact the pistons and the distributor drive seems to line up, but the marks on the cam gears, idler and chains don`t. I pondered someway to compensate the upper chain to make up for what I think is a now one tooth retarded setting on the lower chain, i.e. advance the top chain one tooth. After all, the engine doesn`t know where the marks are, but I can`t decide whether to advance at the idler or the cams. I think I`m just gonna have to start over. This car has very little space to work and the oil pan must come off (again), along with water pump, etc. I will try to do this without head removal, although most manuals recommend it. Any ideas on correction insitu involving the upper cam chain or cams would be appreciated! This is a DOHC arrangement with a lower chain turning an idler gear which moves an upper chain turning the cams.