I use an actual straight-edge ruler, so I have a real number to check on the slack in mm. Using fingers might be a little consistent. During the season after Thanksgiving and Christmas dinners, my fingers might increase my chain slack by 5-10mm...LOL!

 

Keep in mind that the chain is tightest when the rear suspension is compressed and the swing arm is aligned straight out from the counter spocket. I've used a cinch strap to compress the suspension as far as I could get it, then check slack against specs.

 

Yep, getting the countershaft, swingarm pivot, and axle in alignment on their centers gives you the tightest possible point on the chain. Unbolting the rear dog bone mount also allows you to center those points easily. Once you have the tightest point on the chain set at the axle adjusters, you can find the best slack measurement for your bike when the suspension is fully extended. This changes a bit when you change sprocket sizes from what the manual might suggest.

 

Good point. Can you elaborate? I'm assuming that larger sprockets may require a little more slack (e.g. right now I'm running 15/49). But that's just an assumption...and you know where that gets us!!!

 

So are you saying a good guide would be 2 fingers when the bike is just sitting or when the suspension is all the way down?

 

Just sitting

 

Yeah, you can see where if you measure from the same point suggested in the manual, that the rear sprocket is going to be higher above the axle with a larger sprocket, but really, I think the bigger sprockets can also change up how your chain runs on the guides, roller, and rub blocks. This is why the countershaft, swingarm pivot, and axle centers in alignment is really the only way to go if you alter the gearing. With my 47 rear sprocket, I had to move my Hotfoot brand lower chain guide forward just a bit. Some of this also depends on how far back you're running your axle as to chain length. I don't know the geometry and other qualifications as to its effect on chain slack, but whatever setup you're running, if you use that 3-point centering method to find the tightest point, you can then you use the mm number from the OEM recommended location with confidence.

 

Hahahahahaha Nice!!!!!

 

I think the single clack being a chain popping against the chain guide, or, just plain old popping from being jerked tight, is a very astute guess...even if it's wrong, it is one cause of a sound like the one described by the OP!