I'm putting the Trek 500 commuter back together and had a question. This has a 10 speed Campy Centaur compact (50-34 IIRC) and I run a 13-24 freewheel on it. It has a Shimano CN-HG93 chain. I was checking chain length on it, and from big-big, it looks like it has 6 extra links (not thru the RD).

This frame did not have dropout adjusters in it, and the wheel was always run all the way back in the dropouts (probably for tire clearance as the 700x32 Avocet Cross tires are tight). I put adjusters in, but don't have the wheel all the way forward. These are short dropouts also.

1) The rule of thumb is big-big +2 links?
2) If I remove 4 links then wind up having to put the wheel all the way back (w/o adjusters), I might be in trouble
3) Is this the type of chain that you need to replace pins if you end up having to reinstall a pair of links? Not well versed on these new fangled chains and stuff

I'm guessing it needs a minimum of 2 links removed, maybe 4?

Thanks!

Is there any slack when it is on the small/small combo?
If not, there is no reason to remove any links.

And if you break the chain, use a master link (KMC/SRAM/Superlink/etc).
Don't waste time fussing with obsolete manually-installed pins.

Thanks. There already is a master link in (probably forgot that in the count). When I first got this bike last year (from my brother), it had a Shimano Crane RD on it, with wheel all the way back (no adjusters). The chain was slack in the small-small combo. I switched to a Suntour Cyclone Mk II GT when I was riding it last year, and it would take up the slack in sm-sm (not that I use that gear). I am switching to a standard cage Cyclone Mk. II, and since I tore the bike down to the bare frameset to framesaver it, I am going thru everything while I build it up, hence the question. I haven't actually put the chain on yet to see about slack with the current setup, but I guess I will before I do anything about length.

The rule about chain length depends on whether or not you're using a "modern type" of rear derailer (with a sprung upper pivot) or your older Suntour (without a sprung upper pivot).

With the Suntour derailer, the chain length "excess" when on the large/large sprockets should be checked with the chain installed in the derailer, elsewise you risk ending up with a too-short chain, and possibly a no-shift condition when trying to shift off of the largest rear cog.
As Shimagnolo alluded to, you'll have to consider what chain length exceeds the limit of looseness when using the smaller sprockets, although riders like myself never use the smallest sprockets together and thus have less to worry about in terms of a too-long chain.

Keep in mind that a quarter inch of axle movement in the slots will change the chain length requirement by a half inch.

Did someone suggest that Shimano's special (one-time, non-removeable) chain connector pins were obsolete?
Even the latest 11-speed road gruppos use these pins, and with no hint of this changing.
Shimano's pins are very good, but require some commitment as to the installed chain length.
A specially-pinned link can be removed from a chain, but only after grinding the heads fully off of the pins on one side of the link, and then popping the grinder-thinned plate off. A KMC link can then be used if one wants to restore the original chain length, but chains normally don't ever need to be removed until replacement time, or for gross changes in gearing.

I can' t say I've ever lived by this "rule". Consider this: If the chain is too long for little-little (a rarely used combination in my experience, no, make that never used) then the worst thing that happens is the return section of chain dangles loose and the RD cage may wrap around to the back. But if the chain is too short then the big-big combination will break something, most likely your RD in a spectacular way.

I guess everyone shifts differently, but except for the half-step crossover on the Masi I spend most of my time on the big ring. I have once or twice shifted down another cog, having forgotten which cog I'm on, then discovered it wouldn't go down any more. Which is to say that big-big is an easy mistake for me to make.

So just fit your chain to handle big-big, and as long as your RD cage has the take-up capacity you'll be fine.

Thanks for the common sense. I threw the chain on tonight and the derailleur handles the wrap just fine. No point in dealing with this f'ed up chain pin scheme, so will just leave it at this length. I pretty much never use the small chainring on this bike, and would never use the sm-sm anyhow.

Your slightly longer-than-it-needs-to-be chain will also last just a little bit longer, plus you have retained the option to use larger sprockets.