OK, I'm going to show my ignorance here.

I'm planning to build up a gravel grinder from a Trek 520 touring bike frame. The frame has a Shimano triple front derailleur and a Deore LX rear derailleur and an 8-speed cassette. I've sourced a Deore LX triple with a 48-36-26 crankset (new old stock, good price) and the packaging said it's made for a Hollowtech (not Hollowtech II) bottom bracket. OK, first ignorant question: Are modern Hollowtech II BBs compatible with Hollowtech (not II) cranksets? If so, another ignorant question: The BB shell is 68mm x 118mm, and was originally spec'ed for a Shimano BB-5500 bottom bracket. Would that be the right bottom bracket to pair with the LX crankset? Thanks in advance, and I apologize for the lack of knowledge.

68 x 118 is the BB shell width and the spindle length of what is probably an octalink (v1 in the case of 5500) bb. Shimano's terminology here is needlessly confusing. Hollowtech refers to the hollow crankarms. Hollowtech II is the modern external bearing crank/bb standard with a 24mm spindle attached to the drive side running through the bearings, to which the non drive arm is attached on a splined interface, preloaded with a bolt, and held in place with two pinch bolts.

Short story: you have a threaded 68mm english bb shell and need to buy an english threaded hollowtech ii bb marked for use with a 68mm shell.

Bottom bracket standard explained - threaded.

Hollowtech and Hollowtech II are not compatible. You must choose one or the other.

Hollowtech has seperate left and right crank arms connected to an 8 spline spindle integral to the bottom bracket. The 8 spline bottom bracket is called Octalink.




Hollowtech II integrates the spindle with the drive side crank arm. It does not use octalink.

Thank you for showing me the difference. So, if I read this and other replies correctly, I need to match the crankset with an Octalink BB in the proper 68 x 118 size: Shimano ES51 Octalink Bottom Bracket | Chain Reaction Cycles

Yes, the crankset has to match the bottom bracket.

In general, the bottom bracket must be chosen to match the bottom bracket shell in the frame and then the cranks are chosen to match the bottom bracket.

In practice the bottom bracket shell in the frame, bottom bracket itself and crankset are a system. They all should be considered together as such.

But yeah, if you know what bottom bracket you need/have then match the cranks.


-Tim-

The Deore Hollowtech crank on my Raleigh C500 hybrid is square taper
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Interesting.

Hollowtech really refers to the hollow crank arms, not the mounting interface.

my hollowtech bottom bracket came with 3 spacers to go from 68mm to 73mm

Correct It is just hollow arms.
It's just an earlier post implied that the 3 piece "hollowtech" was only octalink when there are also square taper ones out there.

I didn't know there were square taper hollowtech.

If you can find the Shimano part # of the crank, find the Shimano webpage for it, that page should indicate the suggested BB. For instance, this page

https://bike.shimano.com/en-EU/produ...0/FC-M610.html

says (but I know some XT BBs will also work). The page also indicates the crank will work on both 68mm and 73mm BB shells.

If I remember I'll check the model # tonight. 9 speed. I know it's square taper as I replaced the cheap Chin Hauer BB it originally came with.

FC - M510 9 spd Deore triple. These apparently came as either Sq taper or Octalink.

https://freelanderbicycles.com/produ...iple-crank-set

Something isn't right in your description of the new crankset you have. First you say its a NOS Deore LX. But the part number (FC-M510) your providing is just a Deore, not LX. Its from 2000 thru ??, and replaced the earlier STX groupo. So if the person who sold it to you said LX, then they misrepresented it (not by much but still). Two, the chainrings you say are supplied (48-36-26) don't match at all what came with the FC-M510 (44-32-22). This FC-M510 crankset is a 104/64 BCD 4 arm spider; so the rings you are quoting must be after market. You can find the installation manual here; note the rings specified in the documentation Yes there was a square taper and Octalink option for this crankset. You can easily tell the difference between them by looking at your crank arm, and then order the correct one. If it is Octalink, then it is Version II as specified by the BB part number on the installation manual (BB-ES51). Unfortunately, Octalink is pretty much obsolete in Shimano's book, but the bottom brackets will still be available for a long time (hopefully).

Which fail even faster from dirt intrusion - which is the nemesis of most bicycle bearings, worse than water.

Octalink (Hollowtech I) was really a pretty durable and reliable bottom bracket design. The whole concept was given a bad name by ISIS, a public domaine Octalink patent-beater, that had several very poorly made versions.

My experience with HTII, the external bearing format, it that it has been quite reliable. I have them on two daily ridden bikes with 21,000 and 20,000 miles respectively and these bottom brackets are still in great shape.

I'm not the one who identified it as an FC-M510. I just said it was a Deore LX crankset, 48-36-26, new old stock. The crankset is sitting on my lap as I type this, and it is indeed Deore LX, part number FC-M572. 170mm crankarms, in silver and black. It arrived today, and now that I've seen the spline pattern, I'll be ordering the proper BB for it.

Good for you. Not sure that is always the case with HT II, and it doesn't seem to last as long as the previous types of BBs.

As for Octalink, it has a poorly designed crank interface, so the left crank tends to work itself loose if one tends to stand on the pedals (parallel with the ground) with the right foot forward.

Thanks! That's good to know. Fortunately, I rarely stand in the pedals, and on those rare occasions I do, I'm pedaling.

There are two types of octalink and they are not compatible. On e for the road and one for mountain bikes. I found out the hard way.

Mine never loosened in over 30,000 miles and I stand a lot since I like to stand while climbing. That said, I torqued both crankarms to spec using a torque wrench when I installed them so that may have prevented the problem.

Do you stand with the right foot forward?

When a loose one comes in the shop, it's the first thing I ask, to know whether I should suspect a faulty/poorly torqued one, or the design error showing up.

I know this is an old thread, but I have an addition about the ruggedness of the Octalink BBs.
I have two high-end Miyata frames (a 710 and a Team Pro from the 1980 Olympics-branded builds...in addition to other bikes) that have had several different builds (they both came with Suntour Superba groupsets back in 1980). The Octalink cranks wore out in about 10 years after perhaps 25,000 miles, so I built them both up with replacements (the Pro got a Campagnola setup and the 710 got a TA Cyclotouriste)...most of the other hardware stayed constant (I'm still using the Superba brakes on my 'around town' Fixed Gear bike). In the early 21st century (my records aren't so good) I built both bikes up with Shimano complete groups (105 for the red 710, and Ultegra for the Team PRO...both with Octalink triples), upgraded most other stuff too. The 105 is now completely dead and worn out, and I'm converting it to a hill climb machine (FSA 46/30 front and 11-34T rear), but the the Team PRO is still humming along just fine...both of them got a clean and grease about every 3-4 years, but the 710 was my rain bike, and the PRO was my fast group ride bike. I think that the weather killed the 710, but the Ultegra Octalink is still humming fine and probably has 25K-30K miles on it...doesn't owe me a thing.