Here’s how to adjust the primary chain on a Harley-Davidson Evolution Big Twin motorcycle. See my FXR at Inspecting and adjusting an Evolution Harley-Davidson Big Twin motorcycle engine primary chain is pretty simple, and you don’t need any fancy specialized tools to do it. You might as well change the primary oil while you’re in there as well. To adjust the primary chain, remove the shift lever if your bike has one that passes through the primary chain case, remove the left foot peg, remove the primary chain inspection cover, and then measure the deflection of the chain to make sure it is between 5/8″ and 7/8″ (16 to 22mm) at its tightest point. You’ll need to rotate the primary chain and check it a few times to find the tightest point. Harley-Davidson primary chains sometimes wear unevenly, so it is important that you check tension of the primary chain in different positions. To tighten the primary chain, loosen the nut on the motorcycle’s primary chain tensioner and move it upwards. then tighten the nut and measure the chain deflection again. Once you’ve adjusted it properly, replace the inspection cover. Harley-Davidson mechanics told me that putting some silicone on the o-ring on the plastic tube the gear shift rod passes through will stop the primary oil from leaking out near the shifter, so I recommend doing that when you put it back together. If you use silicone, make sure you allow enough time for it to dry before you take your Harley-Davidson Evolution Big Twin motorcycle for a ride.