I just started a long long delayed project of overhauling the 1996 Waterford I bought a few years ago. The bike has full Dura Ace 8 speed (7402), except, when I pulled it, the bottom bracket.

The current bottom bracket (which has been in there long enough to annoyingly rust the cups) is a UN70. It spins fine, although the cup threads look rusted and the unknown mileage on it. Since I don't want to have to pull everything for a long time, I'm looking for a new bottom bracket.

Is there any reason to go with the 'authentic' 740* series bottom bracket? I'd prefer NOS but those are pricey on ebay. If not, should I find one of the older UN73 or 74? Or just get the new new UN54.

Thanks!

I could also get the Phil Wood, but I've never thought they're really worth it.

No reason to use a "real" Dura-Ace BB in it if all you want is a functional bike. Any 113mm length JIS cartridge will work fine.

Pretty sure DA 7400 is 112 and closer to Campy taper, but whatever.

I'd be strongly inclined to use the bb that came out of it. Should last another 30k miles or so.

I've also put 107X70 Shimano bb's with these cranks to give a more-favorable chainline. You'd need just a couple of extra millimeters of clearance between chainstay and the little ring.

The neat thing is that every time I've ordered a UN5X bb in the 70X107 size, it came with metal cups instead of the plastic cups pictured in the catalog.

The taper on the Dura-Ace road spindles is identical to all normal Shimano JIS spindles. I've measured at least a hundred spindles of every type of fitment.

Silly me

Roadrunner, I'm sorry, but that chart is complete BS.

I measure a 7400, 112mm bb spindle right here, and it is 100% JIS

The confusion persists with different brands simply because so few tech's have knowledge of a consistently reliable standard method of reference.

If someone substituted an ISO or Campy bb spindle for the proper Dura-Ace part, it would effectively shorten each end of the spindle by at least 2mm (between 2 and 3 mm each end).

The question I have is who wrote your chart?

I guess Sutherland's is full of crap. I'll toss it in the recycle bin. It seems to be useless.

Sutherlands data is not always accurate:

How it's done: Measuring a JIS spindle.
Note that the caliper jaws are exactly 3mm thick. The point of measurement is thus exactly 3mm from the end of the spindle.
12.9mm=JIS,
12.7mm is more like ISO and Campy,
Old Stronglite is about 12.67mm.
Dura-Ace 7400 spindle shown.


It's always hard to argue with direct measurements, and like I said, I've measured so many spindles over the years, always using the very same method. The caliper shown has been in continuous use for 10 years here.

Hard to argue with the best Harbor Freight has to offer and an expert of such renown. Do you have a manual available for purchase to replace my Sutherlands?

I just wrote down the exact dimensions of three popular standards.

Do you need any others?

I would "X" out that page in my Sutherlands book.
I've had to correct dozens of automotive repair manuals over the years.
Even the $120 factory manuals for Japanese cars have errors.

I should also mention that some of this same sort of bb spindle dimension data found in past Phil catalogs is unreliable, at least to the extent that it is applied to anything other that selecting from the choices that Phil offered. Sutherlands may have made un-verified conclusions based on that, or on other data intended for the application of perhaps other manufacturers limited product offerings.

EDIT:

I also will note that the JIS standard as applied by manufacturers has been the most consistent in accuracy by far.
You can find several hundredths of a millimeter variation in all other standards.

The 12.91mm shown would read 12.90 if I had used my normal two-handed method, but my other hand was taking the picture.

JIS is solid.

Dura-Ace 7400 is JIS.

Sutherlands published data was no good. Perhaps it has been corrected, but it's a little late in the game.
I would like for Sutherlands to at least specify an exact method of measurement for determining spindle taper dimension. They would then be able to re-write their chart if they just had a Harbor caliper handy on their desktop.
I couldn't more than guess as to where they got their data info, but they trusted an unreliable source or two, that much is plain to see.

The Harbor-sourced caliper replaced a good dial caliper here because of it's observed consistency.
It is an unbelieveably good instrument for the money.
I bought a spare 10 years ago and have never needed it.
You can use a JIS spindle to calibrate a lesser caliper!

Isn't a UN70 Dura Ace grade?

I agree with dddd is the spindle turns smoothly there is no reason to replace it.

I do not have alot of miles on my Phil BBs but they seem very nice to me. When I considered the cost of new Record BB for '99ish group compared to the fact I doubt the original had more than 5k on it I went for the Phil.

There is company on the 'bay selling some nice looking and seeming well builf BBs cammed Omni Racer, I put one of their BBs in my Batavus a few weeks ago. it seems pretty nice for the price. https://www.ebay.com/sch/i.html?clk_r...=p5197.c0.m627

Shimano made a cartridge bb called UN91 for the upper-end D-A and XTR groups.

It was a little lighter than UN71 and had stainless steel ball bearings.

A UN-7X bb is silky smooth and known to last many tens of thousands of miles.
I consider both the UN71 and 91 to be the very best square bb's ever made.

I have an update to this thread, in that not all Dura-Ace bb's are JIS.

Firstly though, all 7400 and up bb's are JIS.

But JIS originated, I understand, with Sugino and their Maxy Crank.
This makes sense, because they were perhaps the pre-eminent Japanese crank maker at the time, around 1974 iir.

Just for fun though, I've dug up a 1st-generation Dura-Ace (non-numbered, i.e. no 7***-series number on it) double crank spindle.
This one has only a YF date code and 68 W 112 stamped into it.
I measure this spindle at exactly 12.85mm, measured 3mm from the end as above.

This is interesting, as it is somewhat between the JIS and ISO dimension (JIS is 12.90mm, and ISO/Campy is around 12.7mm), and sounds familiar:
Per Roadrunner 2012:
"Pretty sure DA 7400 is 112 and closer to Campy taper, but whatever."
But this is the Dura-Ace series that came before 7400, so clearly Roadrunner's Sutherlands chart is in error, since the 7400 spindles measure 12.90mm.

But I learned something from this, and if I needed a replacement for this 112mm semi-JIS spindle bb, I could select a slightly shorter JIS 110mm bb to preserve the chainline.

Old thread, but dddd, quick question for you. I have DA 7400 cranks and need a 42mm chainline (on a singlespeed, so single ring up front). I was just going to pick up a Shimano UN5X BB, but I've now read in a couple of different places that BB spindles may not be symetrical?? Any idea what size BB I need? Originally I was going to get a 68 x 107 and run the ring on the outside, which *should* give me a 43mm chainline (which I think is close enough). Thanks for any input.

^ At least from the sutherland's table that rr posted (post 5), it would appear that the 7400 spindles are assymetric. I could see them screwing up on what taper is used, but probably not on the spindle dimensions themselves (A, B and C).

Given standard double chainline is 43.5, which puts the outer ring at 46. You would want 3mm less length on the drive side of the spindle to have a 43 chainline. Shimano cartridge bb's are assymetrical, but I'm not sure whether the non-drive side length changes with change in overall spindle length. 107 or 110 could probably both work for you. I certainly wouldn't go less than 107.

The shorter bb spindles tend to be more symmetric, and I've never seen a spindle shorter than 112mm that wasn't.

Certainly any Shimano cartridge bb shorter than 118 or so should be symmetric, so if you need the tiny bit of offset that the original bb may have had, a 1mm spacer can always be used under the cartridge bb's fixed cup to achieve a bit of offset.

I have here a (March 1985 made) vintage, 113mm Shimano spindle, marked as "D-3H" size designation and also "68=W=113" and "CrMo".

It measures perfectly symmetrical:

30mm from corner of cone shoulder to end of spindle (both ends).

10mm from center of bearing track to radiused start of taper (both ends).

I'd have been very surprised if the same-vintage Dura-Ace spindle was any less symmetrical than this lesser model, since the trend at this time was toward all tapered spindles becoming symmetrical (triples excepted).
But I also find an (October 1984 made) BB-7400 Italian spindle here, marked "70---W" that is 1mm longer on the drive side than the non-drive side, measured as above.
<<<This I would describe as only .5mm offset, since the right crankarm only moves .5mm to the right as the left crankarm is also moved .5mm to the right, thus making the right end of the spindle effectively 1mm longer than the left end of the spindle (yet another measurement-standard quandary?) >>>.