nirusu

I have an issue with my recently built steel fixed gear bike. When tightening the crankarms on the BB, I can easily over-tighten them to the point they can't turn anymore because the crankset makes contact with the BB. I thought that might be normal to not tighten it too much, so I went as far as I could without making contact and called it a day, but after a 10km ride, the non-drive side arm was coming loose. I didn't use thread locker but still, that doesn't feel right.

My gear:

• frame: 68mm english-threaded BB shell
• crankset: Miche Primato Advansed Pista 165mm (recommended BB size: 107mm)
• BB: Tange - LN-3922 68mm Bottom Bracket - BSA 107 mm

Any idea what is wrong here? Do I need to get a longer BB (e.g. 113mm) despite having the recommended size?

Thanks for your help!

Steelman54 

Something is wrong here, are you sure the Tange 107 is the same as the Miche recommended 107? If shorter this could happen. Both crank and bottom bracket should be JIS. So, either it is too short a bottom bracket or crank was overtightened and now cannot be done correct or something weird with crank. No Loctite should be used. Best I got so far.

Iride01 

I don't know if this is fact of not, but I don't think that square tapers whether JIS or other had an accepted distance for the position the chainwheels sat with respect to the end of the BB. So when you buy another crankset of a different make or even different model, you might have issues such as you are seeing.

Your best bet to find the length of the bb spindle will probably be to remove it from the shell. The install both old and new cranks and measure the distance between some common point on both cranks. Then use those numbers to figure the difference that you need to add to the length for a new BB.

If you can still return the crank, I'd go with an ISIS, Octalink or better yet, a 2 piece crank. I believe with them, that the position of the chainwheels was better defined by the standards. These eliminated all the crazy spindle length and offset stuff from the cup and cone BB days that carried over in square taper cartridges because the cranksets themselves didn't have a standard how deep the square taper went on the spider. All IMO of course.

nirusu

Thanks for the prompt reply @Steelman54. I checked the following but no luck:

• I double checked everything with calipers, and the BB size is exactly 107mm long.
• Also the crankset is new so I would assume it was never overtightened.
• Finally both parts are said to be JIS, but I have a feeling that could be the culprit. Any sure-fire way of checking if BB is JIS or ISO (the page on sheldon brown doesn't seem to help me here)?

nirusu

Unfortunately I'm building with 100% new parts here, the crank and BB have both never been used.

Steelman54 

I think Iride01 has an excellent point, maybe go with the Michel bottom bracket, its like 30 bucks.

Arthur Peabody

Torque wrench

Iride01 

Well sort of the same thing then. With the BB out of the shell, install the crank arms and tighten them down. If 2x crank, measure to the center of the bb to the center between the chain rings. That is what chain line that bb is giving you. So what is the chainline needed for your bike? When you know both, then you'll be able to figure out what spindle length that square taper cartridge needs.

I've long forgotten any actual numbers for chainlines because beyond the old square tapers, modern BB's and cranksets finally eliminated needed to worry about this so much.

You can probably estimate the chainline for your bike by measuring the distance from the center of the rear hub to the center of the stack of cogs on the rear wheel. Center of hub being the plane dividing the left side of the hub and bike from the right side of the hub and bike. Or I suppose the mid point between the dropouts. Geesh, this gets complicated describing.

You know what I mean, If I said it wrong, ignore that! <grin>

SurferRosa

I read this as you can tighten the crank bolt to the point where the crank arm is touching/rubbing the bb cup.

If that is the case, yes, you probably need a longer spindle. After solving the spindle length or taper standard problem, familiarize yourself with the required torque for this job.

Litespud

All I could find was the following (from the interwebz, to take it for what it's worth) - if you can measure across the narrowest part of the flats with a micrometer, a JIS spindle should measure 12.65mm, whereas an ISO spindle should measure 12.33mm. Sounds to me like you have a JIS crank on an ISO BB

nirusu

Alright, thx so much everyone for all the suggestions and help!

Based on all that was said, I think I will get a Miche Primato JIS BB 107mm and if that doesn't work, I'll try a 110mm.
The chainline was good with my current 107mm BB so I'd like to keep that if possible.

dabac

You can shim the crankarms.
cut some pieces of sheet metal. Fold to a corner. Trim length to fit crankarm thickness. I like to make some tabs that flare out to keep the shim in place during install.
Doesn’t take much extra thickness to add lateral clearance.

veganbikes

I recall that some Miche cranks were ISO and some were JIS you may want to post in the Fixed Gear/Single Speed sub forum or do a search first (better idea) I know it has been discussed before. You could also reach out to Miche with pictures of the crank (especially those with any identifying marks like serial or part numbers and they might be able to help you.

nirusu

Update: The new Miche Primato JIS BB 107mm does indeed solve the problem!

Despite being advertised as JIS, I believe the BB I received (Tange LN-3922 BSA 107mm) to actually be ISO (or JIS low-pro maybe?). The difference is obvious now that I hold both formats side by side.

Thanks again for you help

Mr. 66

It could be that it was damaged from loosening, your crank may never stay tight as it needs to if it is.