Zantaeus

Lately I have noticed a clacking in my pedals when biking, every time pressure is applied I get a solid click from the crank that I can feel in the pedals and only when pushing down on the pedals. I think the bearings and spindle on my Sedona 21 might be reaching their end as it has not been replaced in the 7+ years that I have had it. Only issue is that I can't find the specific measurements for the spindle so that I can replace it and likely the crank set as well since the main bolts are looking rusty. Any suggestions on what the problem might be or know what spindle a Sedona 21 uses?

Bill Kapaun

The crank used is what determines which spindle to use.
IF you can't identify the crank, you'll have to remove it and the BB to see what size is marked on the BB. (Bottom Bracket)

I presume the bike is a Giant Sedona.
If so, it was made over a bunch of years and would most likely have had several different cranks used depending on the age.
Manfs. can also change mid stream to another brand/model crank.

veganbikes

I would remove the crank and remove the bottom bracket and then it usually will have somewhere on the bottom bracket or the spindle the size and assuming that is the correct size you can get a new one with that spindle length. Usually it will be 73x180 (which is made up but it would be usually the bottom bracket width and then the spindle length). Shimano makes the UN-300 which is a solid lower cost option but if you love the bike and it is a decent bike IRD Defiant QB-95 is a higher end option or if you want the longest lasting probably SKF or Phil Wood.

Duragrouch

May be bottom bracket. May also be pedals, check those first. Usually will click on one side but not the other unless both have been neglected. Easy check would be to swap in known good pedals to see if click disappears. But if you pull the pedals off and just rotate the spindle in your fingers, if it's anything but glass smooth, I'd suspect. I've rebuilt the same set of pedals many times, last time I replaced the balls. Oh also, some cheaper pedals have a stamped bearing (outside) race, which will often crack, causing the click and a loosening of the pedal on the spindle. Check the pedals first.

Iride01 

Clicks might be the pedal. Try some other pedals and see if the click you feel is still there. Or just clean, lube and adjust the pedal bearings if it's a serviceable pedal. I've never had a BB that clicked. Not saying it doesn't happen, but I've had pedals that let me feel a click on the downstroke when applying power.