JustinHorne

Hi all,

I recently came into posession of a 92 Bridgestone RB1. The prior owner, due to health, had converted from the stock double to a Mavic 631 Starfish triple.
If you're curious, it looks like this:



My plan is to convert this significantly closer to a stock/period correct build (tricolor, Nitto Pearl, DTs.) Well, due to my lack of knowledge of this specific crank, I thought it would be a simple matter of buying a Shimano crank and possibly a new spindle. Those in the know already know I am wrong.

It turns out that this bike has been swapped to the Mavic 610URD, with associate 45degree taper/ facing. It's got a 119mm spindle.

I found this excellent site which details the BBs and installation info: Mavic bottom bracket, the road to perfection - Le Cycleur

The site mentions: To properly mount it, the bottom bracket box of the frame needs to be re-faced with a 45° chamfer to fix the chamfered mounting rings. Obviously it removes the outer few threads of the bracket which sort of eliminates mounting another type of bracket in the future. But why would you revert to a lesser bracket, right? It is scary at first, but with the proper tools it’s a piece of cake.

Given that I have a 7400 series double crank sitting in a box ready to go, that was a bummer.

So here's basically my questions:
1) I'm not opposed to using this BB. I'm pretty sure it cannot be, but to double check, can it be used on the 7400 series double? I have a 119mm spindle and Sheldon said 112mm for an English double. Also, this confident-sounding BF post pretty explicitly states that, even despite some evidence to the contrary, it's decidedly not a JIS taper and that's that: Let's talk about the Mavic 610/616 bottom bracket
2) Am I really completely out of luck for installing a different BB into this frame?
3) Any other suggestions?

Worst comes to worst, I'll pull the triple adapter off the starfish and use it as a double... I just really wanted to put a 7400 crank on this frame.
Appreciate it!

panzerwagon 

If the Mavic BB is otherwise in good condition, you might consider test-fitting the crankset and measuring the chain line. Differences in spindle taper vs crank expectations might even things out a bit, provided the arms don’t bottom out
on the spindle.

Alternatively, I have a double version of that BB (along with the corresponding starfish double crank) on the shelf if you need. I can take measurements this weekend if interested.

Finally, don’t most vintage BB cups have enough threads to sufficiently engage the remaining threads in the shell, beyond the chamfer?

JustinHorne

Re: Taper. Definitely an option. As a general rule I really try to do things 'right' so I get a little nervous at the thought of mismatched tapers, but I also understand that current views of 'compatible' are different than 'compatible' 30 years ago. That's an option.

If I had to bet, I'd guess you've got a 114mm spindle? One challenge at a time (as it seems my 'floating' bb no longer... floats) but I suppose I could always just recenter the BB a few MM to the NDS as well. Perks of the Mavic design I suppose.

Finally, don’t most vintage BB cups have enough threads to sufficiently engage the remaining threads in the shell, beyond the chamfer? This was my thinking as well. Tapering should have only removed a nominal 4mm of threads. Once I get the BB out I will inspect. If there's just 2 mm of tapering per side backed by a solid 2cm+ of threading, might just go for it.

E: Perhaps I could just buy a VeloOrange sealed BB in english/113 or a UN71. I'll check the threads tomorrow.

Velo Orange English Threaded Square Taper Bottom Bracket (velo-orange.com)

blamester

I have the same chamfer. I installed a shimano bb with no difficulty or issues since. There was sufficient engagement that it made no difference.
Try it and see.

masi61

I have one of those Mavic Starfish triple cranks in perfect condition that I purchased from eBay. I have been looking for the correct bottom bracket for it. I have even been looking for the 45 degree chamfering BB tool at a reasonable price. Finding a 119mm bottom bracket that is for a standard 68mm British head bb shell is probably the route I will go though so I don’t have to do the chamfer thing.
As for your conversion back to a standard bb, I have read that even with the chamfer, there are still plenty of remaining threads to install whatever conventional bb you want.

Bianchigirll 

If you have access to the tools, I'd face the BB just because it would be a good idea but with the few I've seen going from the Mavic to Shimano I don't recall any problems. Are you using a cartridge BB? I belive the threads on those are deeper anyway.

jamesdak 

I had a Concorde frameset a few years back that came set up with a Mavic tapered BB. While mocking up various build options on it I was still able to install a normal BB with plenty of thread engagement. I even seem to remember seeing online instructions somewhere for the BB mentioning that you could still run a normal BB after tapering the BB shell but don't quote me on that.


Sourced a Mavic Starfish crank in the end as I liked the look on this bike.

repechage

Most traditional BB cups terminate threading 1.5mm before the end flange on the fixed cup, I would suggest a steel lock ring on the adjustable cup but basically there should be no problems.

unworthy1

agree with all who say you should still have sufficient threading left on the BB shell after chamfering to install a Shimano (Tange or any other sealed BB unit, and maybe quite a few old conventional "open BBs" plus Phil or VO) with no issues.

And nobody HAD to use a Mavic "no threads, m'lady" BB unit on that Starfish crank, either, it just had to be a BB spindle with the proper ISO taper for the crank (versus the JIS taper of most all Asian BBs and spindles), but if any consolation the Mavic does have very good quality bearings and chances are they are still good after decades (but so does/do Phil Woods).

Retoocs

I've been running my Mavic crank with Phil Wood BB since the 90's. Still spins smoothly.

JustinHorne

Fantastic, thanks for the help, all. And yes, to those who mentioned it, the Mavic BB is still buttery.

A little update (and it seems good news.)

There was a bit of rust between the BB shell and the bb (actual rust, not galvanic corrrosion) that likely came up through the cable guide. I was able to get the Mavic BB out without too much persuasion:



As predicted by many, it appears that there are tons of threads left.

Unless anyone sees any red flags, I'll treat that rust, have my LBS retap and face it, and go with a UN71.

JustinHorne

Alright, one more update (hopefully helps someone else in the future too.)

I wire brushed, treated the rust, and had my LBS tap the threads just in case. Probably unnecessary but some easy insurance. I'm probably gonna go with a Tange 3922 or 7922 depending on what I can find, then hopefully all good to go!

Chombi1 

if the threads were good before the chamfers were cut, the they should still be good to take on a conventional BB with no problems. It would be good though if the existing threads can be chased to get rid of any possible burrs at the start of the threads, left by the Mavic chamfering tool. You can get it done b6 a good bike shop with the correct thread cutter.