Bicycle Mechanics - BB Trek 700

I thought it would be a sealed unit, but was surprised to find cone and cup when I opened up the bb. I found that the inner bearing surface on the axle was wasted.

I found another reference for a size on that bike to be 68x116. I find sealed BBs with the sizes of 68x115 and 68x118.

Bike is all stock.

What shall I use to put it together right?

TIA,

-SP

since you have the original bb just measure the spindle yourself

Let's assume it is 116mm, so the issue is do you go up or down 1mm.

Usually I tell people to look at the chainstay clearance on the right side and see how much room they have. Consider 2mm a minimum safe distance leaving some room if a chainring bends slightly. Then if you have spare room you can go shorter, otherwise longer.

Since you're crank is off already, you can toss a coin. 1mm isn't much so odds favor going shorter will be OK. Or you can play it safe and go 2mm longer. Remember, that not all are symmetrical, nor do cranks go up the same distance on the tapers, so the actual difference may be more or less than the difference in the spindle length.

Thanks FB. Another annoying bit- There is a split plastic spacer around the axle. I tried a couple of ways to open it and get the axle out. Any good secrets for getting a release?

-SP

I've got two Trek 700s (had a third but sold it recently) of 1990s vintages and I've put Shimano UN54 BBs in all three. The stock configuration left plenty of room that a 1-2mm change in either direction wouldn't cause any trouble. Yours may be an older model being it had a cup and ball set up but I am confident that either the 115 or 118 mm spindle will work just fine. Your decision will affect the chainline by about the width of one rear cog, so if you like using small cogs with the middle chainring, look at the 118. If you ride mainly in your big chainring, I'd pick the 115.

Though not the lightest framesets around, I'm a fan of the 700 series for quality of ride and bulletproof durability. One nice upgrade to a basic 700 is to find the fork off a 730 which is chrome moly. It's slightly lighter and has a bit more spring to it. The stock fork is fine but you will notice a reduction in fine road vibration with the 730 fork. You can get aftermarket chrome moly forks but they don't quite match the original and always look like a replacement, a fork from a 730 looks stock.

Thanks FB. Another annoying bit- There is a split plastic spacer around the axle. I tried a couple of ways to open it and get the axle out. Any good secrets for getting a release?

-SP

By plastic spacer, if you are referring to the sleeve that keeps dirt from falling out of the tubes and into the bottom bracket, that should push right out. There should be nothing holding it in if you have removed the bearing nut on the chain side of the BB. If you have not removed the Drive side (chain side) nut don’t forget that it is Left hand thread, turn clockwise to remove. If both nuts are removed the BB should look like the picture below. As you can see there is nothing to hold the sleeve in once the nuts and axle (spindle) is removed.

268412


As far as the length of the spindle is concern either length will work. If your spindle has square taper ends then I would go with the longer spindle. With tapered ends, each time you remove and reinstall the crank arms the arms go a little bit further up on the taper.

....so if you like using small cogs with the middle chainring, look at the 118. If you ride mainly in your big chainring, I'd pick the 115.

+1

Sometimes we get so obsessed with a perfect chainline that is only perfect in ONE GEAR.
I fudge a bit wider because I tend to use the middle ring with the smaller cogs.