What chain should I use?
 

I just obtained a 1987 Trek 560EX. It has all its original components which are mostly all Shimano 600. It has the two "Biopace chainrings" that I intend on keeping at least for now. My question is what chain is compatible to this bike? It has its original 6 speed cassette on the original rear wheel.

There are Shimano , KMC and Sram 6 speed chains that will work. Go to your LBS or go on-line. Cost range $10 - $15. You may even look at buying a new cassette for less than $25.

Anything marked as 6, 7, or 8 speed will work.

+1

The newer chain will work much better than the original, 6-speed width chain. More clearance at the front derailer cage, more-forgiving downshifts, less sensitive to adjustments, and newer chains are almost always quieter.

izumi chains only cheap and the best

3/32 wide , generic ..5,6.7.8, 9 requires the chain be narrower,
till you get tha far the cheaper width will work.

the Sram will last longer than any, the shimano may shift a little better but you may not notice the difference

My own experience has been that Shimano chain out-wears (out-lasts) every other. I'm including the more modest-level Shimano chains here.
I've also noticed that Shimano chains require less lubing. I assembled a chain from 2 lengths of chain, Shimano HG73 and SRAM PC59, and used it for over a year now. Always it was the SRAM length that started squeeking first. I lubed the entire chain with WL with 30% mineral spirits and 1-2% motor oil.
I replace chains that are approaching 0.5% stretch, but still get several thousand miles of road use, so wear is the minor issue.

Yep. I'm set on SRAM chains with their Powerlink, which makes for easy chain removal and installation if that's something you care about.

I like SRAM for the powerlinks, though I have also used them on Shimano 8 and 9 speed chains successfully. Really I have not encountered any which are markedly better than others, all seem to work fine. Some people seem to be more sensitive to chain differences than I am.

Dayum!
Now there is an idea!:thumb:
Assemble a chain with Shimano/SRAM/KMC/Campy/Wippermann sections to do a direct comparison of wear.

Note that SRAM 8-speed Powerlinks don't fit Shimano 8-speed chain, save for two out of the 4 or 5 "IG" model chains.

Powerlinks won't fit any 8-speed "HG" chains, but there are several other brands of link that will.
A heavily-worn Powerlink perhaps might fit on a Shimano HG 8sp chain, and a new Powerlink might fit on a heavily-worn HG 8sp chain, but I mean "heavily" worn! The Shimano inner link is wider.

9-speed Powerlinks seem to work on all 9-speed chains.