A few years back I bought an njs frame from a friend for $300 with a 103mm JIS phil wood bottom bracket. I then scored some dura-ace FC-7600 cranks. Had a friend install the cranks and was good to go. Ran that for about 7 months until the phil bottom bracket took a ****. The PW bb was already pretty used and well-loved before I got it. Took it to a shop and they swapped it out for a JIS 103mm sugino messenger bottom bracket.

Recently sold that frame because it was too small and got another njs frame and installed the same sugino messenger bb.

Been riding just fine these past 3 years except my chain gets loose fast. I'm talking 40 miles. Figure that's me needing tensioners though.

So.. I looked online and the Dura-Ace fc-7600 cranks are supposed to have a 108 JIS bottom bracket (Phil Wood said the same). My chainline always looked about dead on. I picked up the phil bottom bracket today from the shop and the mechanic kinda scratched his head. Saying even though the specs say 108 that my 103 is just about spot-on and that the 108 wouldn't really make a difference, other than having $200 less in my pocket. So I got my cash back.

I guess what I'm getting at is this:

How am I riding a 103 JIS bb with spot-on (or respectable at least) chainline when fc-7600's are clearly supposed to have 108 JIS?

Also, if it is so slightly off what do I have to worry about? Chainring/cog wear? I've NEVER dropped my chain. It is pretty noisy but I figure that's what you get with a 1/8" setup.

ive never heard of a phil bb ever crapping out on anyone. ever.

bearings wear out and like i said, that bb was used and well-loved (beat to hell). but thanks for your input.
my question has nothing to do with the life-span of phil wood bottom brackets.

Well, is it spot-on or is it acceptable? Bust out the ruler and take a chainline measurement.

Proper spindle length for the FC7600 is 109mm. Seeing as how both you and the mechanic got this wrong I'm betting this is just a measuring (including the chainline) or ISO/JIS error and nothing more.

Will measure today, thanks. If the 108 would indeed be spot on, that means my chainline is off 2.5mm.
Other than chainring/cog/chain wear would there be anything else to worry about? I've been running the same phil wheels, zen chainring and phil cog for about 2 years. Obviously the chainring/cog have some wear but seems about normal for the amount of riding I'm doing. Someone told me to watch out for extra play in the hubs? Not really sure how to notice that..

the phil bb spindle can be adjusted a few mm to the left or right to get proper chainline, but 103 to 108 is a huge jump. hows the clearance for your crank arms on both chainstays?

you invested in all hi-end stuff: an njs frame, da cranks, phils wheels (did you mean hubs?) & cog, etc
you also mentioned that your "chain gets loose fast. I'm talking 40 miles."
yet now that you learned your bb spindle is the wrong size you are actually considering settling for "will it be ok?"
you don't want to spend a few more bux to actually get it right?

a 1/8" chainring is ~5mm thick, you're off by half that. No wonder you can't tell, feel it or need to fix it.

I agree with both. The difference is small, but if you're making a big deal out of it then measure it and use the correct BB.