Weekendtinkerer

I've got a Miyata 100 with all the original components. It has a double crank set on what seems to be a normal JIS interface. If I simply remove the crank set with a crank puller and buy a modern triple crank say 42/32/22 can I simply press it on or will I need a longer spindle length. It seems to be a standard 68 mm BSA I didn't measure the spindle but that's not really the issue right shouldn't the JIS interface be the same length on a single double or triple crank set?

Russ Roth

No where near enough information to provide an answer. You'll need to know the length of the current spindle and the required length of the new crankset to know if its a possibility. But even then, brand A might have 20mm sticking out the drive side on their 115mm spindle to accommodate their spider and chainring layout, while brand B has 16mm to fit their crank setup. Usually there's no problem within a brand but switching brands the only way to know is to try. Going from a double to a triple however will make it highly unlikely that you will get away with the old BB. I'd just buy the one that matches the new crank and save some hassle and slowdown. Worst case, try anyways and if the old BB works than you have a backup.

Weekendtinkerer

Well when I do Resto mods right now if I get a square taper crank set I'm only checking the spindle length to make sure it clears the chain stays. So whether I get a single a double or a triple JIS interface I never check I just screwed them on they usually fit. But this bike is from like 81 it's definitely Japanese so it has a JIS. Aside from obviously the bolt getting tight LOL how do I know if the interface is into the crank set all the way. If it goes too far obviously I'll know when it touches the frame or something or if the arm doesn't clear I just thought someone would know off the top of their head. I guess I'll just press it on and see how it seems

Kontact 

Aside from some bizarre coincidence, you are unlikely to find a triple crank that works on your double spindle to make correct chainline.

"JIS" describes the end of the spindle, not its length. There are dozens of lengths to accommodate different cranks and there is not standardization.

Weekendtinkerer

see my response to the other user. Im aware of what the jis is i jist didnt know if the interface ever changed. Like if I try to buy a triple tourney crank set right now it doesn't say what length to use it with the bottom bracket because the chainstays vary so much for crank arm clearance. And different size bottom brackets. Normally if it says JIS I can put it on literally any JIS fitting I just wanted to know if that's always or if that's just since like the 90s and now

Bill Kapaun

These are not all of the "British" spindles, but it shows there are MANY lengths.


Find out what the CRANK requires.
Trying to do it the other way is like finding a tire and looking for a vehicle to fit it.

Kontact 

Well, that's all wrong.

Spindle lengths aren't based on the frame, but on the chainline that the crank is designed for. The chainstays are designed to work with the chainline the bike is built for.

Generally speaking, there is one and only one correct spindle length for a given crank. Dura Ace 7400 was 114mm, but 7410 is 103mm. Swap them and you'll have one crank crushing the chainstay, and the other will be sticking out so far the front derailleur won't reach the outer chainring.

You can often get away with wrong length because it is close enough, but it is still wrong and makes the chainline wrong.

Hondo6

Required spindle length for a square taper crankset is typically dependent on the crankset itself and the chainline required. For more modern triples, the chainline can be either 47.5mm or 50mm, which may be affected by the frame.

You indicated you were looking at Tourney triple cranksets. For a Shimano FC-TY501 or FC-TY301 triple, Shimano specifications for 2022-2023 say that the BB required is a BB-UN100 or BB-UN300 D-NL (47.5mm chainline) or D-EL (50mm chainline). For a Shimano FC-TY801 triple, the BB-UN100 LL123 is specified.

The Shimano specification pages for the BB-UN100 and BB-UN300 appear to indicate that the LL123 is 123mm in length, while the D-NL and D-EL appear to be 122mm and 127mm, respectively. However, Shimano doesn't indicate the degree of asymmetry for any of these spindles, so figuring out what old-style cup and cone spindle is equivalent may require a fair degree of trial and error.

If it were me, I'd probably get and use the cartridge BB that Shimano recommends for whatever crank you're looking at. For a Miyata 100, being an older frame I'd guess the chainline required for a triple is likely 47.5mm.

But it's your bike, so do what you like.

Weekendtinkerer

Thank you for the response, I checked Sheldon brown the chain line is 45 for the Triple crank. I'm just going to press the triple onto the existing bracket and measure. If not I will grab a new cartridge bracket and hopefully calculate how many millimeters to add based on where the chain line appears on the existing one when I press it on. Thank you

Kontact 

You can also look up the crank on velobase and see what kind of spindle it is designed for. If it is an asymmetric, Sheldon lists that symmetric equivalents for cartridge BBs.

Weekendtinkerer

once I remove both crank arms I can measure the exposed part of the spindle on either side if it's symmetrical it will be the same? Is that right

Kontact 

No. We don't care about the old spindle. The important part is the crank. Look the crank up and see what kind of spindle it has, and sometimes you can tell from the crank listing or the listing for the associated BB if it is asymmetric.

Here's a listing:
https://velobase.com/ViewComponent.a...115&AbsPos=356

Hondo6

Might want to check that again. The late Sheldon Brown's website gives two different Shimano specifications for a triple crank: 45mm for road, and 47.5mm to 50mm for MTB.

I'll also note that Sheldon Brown has been gone 15+ years now. There have been a few changes in bicycle technology since his demise.

Tourney is a Shimano MTB product; you're talking about putting it in a road frame. A 45mm chainline might work acceptably for a Tourney crank (presumably a current one) in that frame; it might not. Above, I was just telling you what BBs Shimano recommends you use for their current Tourney cranksets - presumably because that's what they're designed to use. Deviate if you like.

Best of luck.

70sSanO

You are on the right track to test the crank out on the existing spindle and then measure the chainline and inner chainring clearance. If nothing else you will be able to calculate what you need. You should also measure the NDS crank arm clearance.

I’ve put JIS square taper mtb crank on a road bike by matching a cup-cone spindle to what I needed, and maybe a bit of luck having one that worked.

John

Iride01 

If you are changing cranks, then why not change to a BB type that doesn't leave you having to wonder what the chain line will be with ABC's crank on a particular BB spindle length compared to XYZ's chain line on the same spindle length.

Octalink II or ISIS cartridge BB's will eliminate some of that and make things easier. It'll also open up a lot more cranksets for you to chose from. If you go 2 piece cranksets, then even more selection and simpler consideration as the nitty gritty details are built into the design standards.

70sSanO

The issue with an Octalink II is the OP is using a mtb crank with a 50mm chainline on a road bike.

Octalink doesn’t offer enough spindle variability to make it work.

I just finished doing a 1x9 with a Deore Octalink triple crank in a 68mm BB shell. I used a 1x chainring with a 2mm shoulder moving the teeth in, and a BB for a 73mm shell which gave me another 2.5mm. This moved the ring 4.5mm to give me a 45.5mm chainline. I did use a NDS cup for a 68mm shell and it still protrudes out a few mm’s.

John