skully ferguson, "you need to remove an inspection cover, which has a reusable rubber gasket. With the cover off and the transmission in neutral, you push up on the chain and measure how far the chain moves when you push up on it. For a big twin it should be 5/8 to 7/8 inch (16 - 22 mm) when the engine is cold, and for a Sportster it should be 3/8 to 1/2 inch (9.5 - 12.7 mm) when the engine is cold. This measurement is for the TIGHTEST section of the chain, and chains do sometimes wear unevenly and get stretched in places. For this reason, you should rotate the chain 5 or more times and re-check the adjustment to find the tightest spot in the chain before doing any adjusting" there is a decent video about it right here. Hope this helps, good luck.