Ex Pres 

JeffP, it's not hard to find the correct 113mm Italian 740x BB and/or spindles. I have 2 bikes equipped with them, and didn't pay up for either.

Edit: I looked at ebay - the current listings' offering prices are ridiculous.

cyclotoine

I think you may find success with a 1980s campagnolo bottom bracket also. 111mm might be a little short (later chours/athena), but a 115mm might be a little too long, but pretty close. I would try a record double BB, post CPSC and see how it goes.. I think the italians were 114.5mm. If I read all the evidence closely I conclude that your cranks are ISO so I would stick to ISO spindles.

jeffpepperdine

The more I read about this the more confusing it seems to get. haha. Looking at the photos posted in this thread, and through other documentation, it seems that the 7400 crank fits close to ISO, but the 7400 bottom bracket seems to be closer to JIS standards (as per this thread). Which means I would want a JIS spindle near 113? and the crank would fit deeper on a ISO spindle, so it would need to be 115+? Or maybe I'm a confused sole. Regardless, I'm trying to establish an affordable route; if I wanted to spend $90 there are plenty of NOS 7400 BB's on ebay.

cyclotoine

I think that it might be JIS "low-profile" which is closer to ISO/campy. So I think to say the 7400 BB is JIS is mis-leading. You could try the JIS spindle, but I would try something even shorter than 113. You could always go to recyclistas and test fit a bunch of BBs. Personally, I'd rather have the crank engauging more spindle so I would use a campy BB if it works.. or I'd just buy the NOS one off ebay. $90 ain't bad given the quality of the BB.

dddd

I'm the one who measures all the spindles, and who posted.

The picture was intended to show clearly that 740X-series spindles are JIS. All of them, and not "part-JIS". I have verified this a few more times since measuring the exact JIS dimension of 12.9mm (measured 3mm from the end).

Campag spindles measure in the 12.7-12.76 range, while other ISO bb spindles measure as small as 12.65mm, so that is completely different territiory from the totally-consistent JIS 12.90mm.
Even low-end JIS spindles from every manufacturer are totally accurate based on perhaps hundreds of spindles I've measured.

There were pre-740X Dura-Ace spindles that did measure slightly small, but only from that early generation, and the difference was slight (only a few thou at most).

I would go for a Shimano cartridge bb, since they seem to last forever, are very economical (bargain of century imo) and are also at least as light (or lighter if it's a UN7X/9X) as the original 740X bb.

I usually select a shorter, 110mm cartridge unit for 740X cranks (to improve chainline) if there is an extra couple of mm between the small chainring and the chainstay, which can be fine-tuned with a spacer under the cup flange, later, if needed.
I've even used 107mm once (on my Merckx), since that was the only length less than 113 which came Italian-threaded.

I don't understand why folks prefer cup/cone to the newer units, especially considering that both XTR and Dura-Ace gruppos evolved to the lighter, longer-lasting cartridges.

Lastly, the 2-letter stamping is the date code.
1st letter is the year, A=1976, K=1986, and A=2002 starting again. 2nd letter is the month.
Pre-1976, the 1st letter changed approximately quarterly, or 4 times per year.

Shown is a 740X spindle being measured.

jeffpepperdine

Thank you dddd,

I believe this post really pulls everything together. I am happy to hear you've successfully used shimano cartridges.

This morning, before doing my research, I ordered a 115. I have since changed it to a 107 (which was the only other italian this particular supplier had available). I will try this when I get it and hope for the best, and if not, will order another in 110 or 113.

- J

dddd

Hopefully you won't need much or any of a spacer, but if you do there is no worry of losing your lockring threading on the other end if the (cartridge) bb is moved over more than a couple of mm (Shimano's cartridge units and most others have no lockrings).

And by the way, "low profile" is used simply to refer to a style of crankarm that uses a shorter bb spindle, as on the final 7410 version.
There is no "low-profile-specific taper".

cyclotoine

what do you make of the phil wood, low profile JIS taper?

miamijim

Awhile back I did extensive measuring and comparisons of the ISO and JIS tapers, my conclusion was that the angle of taper was almost identical but what changed was the cross section area. Think of a triangle, JIS is at the base while ISO is closer to the top. Phil taper is somewherein the middle.

Jeff, I have an Italian DA BB available....

miamijim

https://www.bikeforums.net/showthread...1#post10560897

https://www.bikeforums.net/showthread...?highlight=iso

jeffpepperdine

Just an FYI, I'm way to cheap to pay the $90 asking prices on ebay right now, but please let me know what you have / condition, and how much you want for it shipped to Victoria, BC.

Your detailed research in this field is much appreciated.

Regards,
- Jeff

jeffpepperdine

I realized last night that I had a 113 UN54 English thread in my bin. And given that English threads are a smaller diameter than Italian I was able to slide it right in. The Crank is torqued on. I've got ~3-4mm of clearance right now. (113-107)/2=3mm. So it's going to be close with the 107 spindle. If it doesn't fit, I may be able to get away with a 1 or 2mm spacer on the drive side, as noted by dddd.

Interestingly, the chainline with the 113 spindle is ~145mm which is well over the recommended 142.5 by Sheldon. So if I can shave a few mm off, I'll be laughing.

Lastly, assuming there is some flex in the crank under load, how much clearance do I need between the rear stay and the small ring to be safe?

dddd

I'm of the same opinion favoring a shorter chainline for a few good reasons.

I like to see about 2mm clearance to the chainstay, to cover for years of use and maybe one good re-torquing.
The small chainring size affects the clearance. Your photo shows very generous clearance.
I have sometimes used belt-sander paper held stationary against the chainstay to machine down the rotating chainring. Some thicker/better rings have a ridge/step or lip "corner" below the teeth that can benefit from being cut down. I protect the chainstay paint with tape first, as even the smooth side of the paper will be showered with abrasive dust. The tape thickness can be adjusted to regulate the "feed" of the cut.

I could only recommend a bb that I've measured, but at least the Phil bb's are laterally adjustable.
Don't forget to get a Phil splined tool if you don't have one already.
I am usually wary of any published taper descriptions from catalogs including Phil's or even Sutherland's.
There are some generalizations sometimes applied that can affect the effective length of a spindle, but I've always found JIS to be very exacting vs. other tapers.

jeffpepperdine

Okay. One more question.

I received the 107 bb that I ordered a while back, and finally had a chance to try it last night. With it, I've got about 0.5mm of clearance between the small ring and the chain stay, which I am definitely not comfortable with. So, I have two options. Buy a new 110, or put a spacer on the 107.

I probably would just go the spacer route, except I ran into another quirk that I haven't had to deal with before. If I space the drive side out 1.5mm, then the non-drive side cup will recess into the bb shell another 1.5mm. This will start to expose a few threads of the bb shell. This would then be a collection point for water, and corrosion. This must be a common issue with spacing shimano cartridge bb's, but I can't find any reference to it online. Thoughts?

Thanks,
- Jeff

spacemanz

Interesting thread here. I'm very new to using Italian threading, as in only used it in the last 3 months or so. I knew that the BB shell was 70mm instead of 68mm for English threading, but I had no idea the tapers were like this, for the Shimano 7400 & 6400 cranks, which I happen to have both of. I currently have the 6400 cranks on the Miele (closest I have to Tri-Color), with the F*G Italian-threaded BB, and everything "seems" fine, by eyeball, though I haven't run cables yet, just a chain. I'm not fully understanding all this yet, but it sounds like I "accidentally" found a pretty good combination, no? I had read that Campy & Shimano weren't really interchangeable, so I was wondering why mine worked this well, & thought maybe something was worn, in a very fortunate way, LOL. BTW, I also have a newer Campy Veloce BB, and it would be pretty cool, if I could use the 7400 cranks with that. Not that I will, but it's useful to know, just in case.

jeffpepperdine

There is a good chance that it will work with a campy bb, but I would wager that in order to get clearance and a decent chainline, your spindle is at least 115... Google just told me that a newer veloce bb comes with a 115.5 spindle. I have to be honest, I'm incredibly jealous of the accidental success.

furballi

I always check the chain line before upgrading the BB. The stock on one of the bike was 122.5 mm. Optimum chain line was 118 mm with the 8-speed cassette, so I ordered a cheap 118 mm UN55 BB. You can always fine tune the chain line with aluminum spacers (1-3 mm). If the small chainring is about to make contact with the frame, then you need to add at least a 3 mm spacer to the drive side.

jeffpepperdine

Appreciate the advice. I didn't have a bb to start with, so I wasn't able to determine chainline / clearance until I tried a bb.

Further though, what do you do about the non drive side cups on shimano cartridge bottom brackets when you are using spacers? It will dissapear into the bb shell leaving thread exposed that could rust.

furballi

The UN55 has at least 3 mm exposed on the non-drive side.

The Shimano BB-M952 (BC1.37x24 Octalink) comes with spacers on both sides. I added 3 mm to the drive side, and 5 mm to the non-drive side of my Bridgestone 400.

dddd

I've just assumed that the grease in the threads will keep rust away, at least here in dry California.
And I wouldn't intentionally ride my merckx in wet weather or on wet roads normally.