Yesterday I took out my car after I got the cylinder head back on and every thing buttomed back down. After taking it on a 5 mile drive, when I parked it I noticed white smoke is still coming out of the exhaust. The car is '91 300 CE. Could it be residue oil still in the exhaust from before the rebuild, or is it something else? I've read where the engine will still start and run even if the timing is off a little.