xifias

Hello to everyone,

Got my hands on a used yet near new Chorus crankset that due to insufficient tightening,the hirth joint weared out causing poor allignment.Also a bolt split failure maybe is related to that incident.

Is it possible or does anyone know how to repair/restore the original shape of the teeth that are near parallel on sides and flat on top?

on the left my worn out and on the right an off-the-shelf new one crank arm.

Bill Kapaun

A welder & milling machine.

maddog34

and a custom ground cutter... and the milling machine should probably be a horizontal spindle type... and you'll need an indexing fixture, too... and a year or two of college level machine shop tech. education(Welding is a required module)..... etc.

should only cost about 20 grand if he shops carefully...

to the OP... get a new crank. upgrade to a Hollowtech II that doesn't have failures like Campy cranks of your type do.... and are typically lighter and stronger, but aren't as pretty to stare at.

xifias

I already put the old 105 5600 back but it isnt as light as the chorus (over 150gr heavier) not that its important to me,but sure it isnt as pretty as you mention.
But..the chorus is almost unused condition,clear coat has no marks,chainrings too.must have less than ~1000 klms at very max,yet very unlucky installation..

Some sort of welding or metal filler and cutting would be needed for sure..dont know exactly how it can be machined after,due to the arms..
but it is very strange that on the whole internet no one ever came up to a similar situation..Only the rogue's mechanic issue about spacers comes up over and over again after googling,along with some installation videos and thats all.

nfmisso

The one on the right in the picture was made on a 5 axis CNC; it looks like EDM wire cutting to me, but could be of been milled. If it was wire cut, it would have made sense to make it out of a really hard steel, instead of one the wore out fast; which points towards milling. There is nothing short of 5 axis CNC system that could make those cuts precise enough to use for their intended purpose. Any sort of cutting (machining, filing, etc) short of that may result in parts that look okay, but will not function properly.

For a limited production run (say 10K pieces); I'd have them investment cast out of a high grade alloy steel that can be hardened to Rc60 or higher, harden the parts, then wire EDM and polish. In China, that job would run around $250K (tools, parts and processing); so $25- each, plus business overhead, wholesale would be around $100-, retail around $200-. The parts and processing at higher volumes would plateau around $10- each ->~$100 retail.

Based on the fast wear, some probably just ran some 416SST bar stock thru a CNC Swiss for about $5- each plus a day's programming & set up.

Marcus_Ti

Hirth joints are complex things to make...which is why you never saw them on a bicycle crankset until this millennium....one of the few things I think you can actually say is "new" to a bike.

Buy a new crank.

alcjphil

What makes you believe that Hollowtech II is an upgrade? One of the reasons that Campagnolo did not migrate to outboard bearing bottom brackets or even previously to bigger spindle bottom brackets was because of two things, reliability and ankle clearance. Large spindles inside standard bottom bracket shells require smaller bearing balls, reducing reliability. To have a low profile crank for people who need additional ankle clearance isn't addressed by Shimano HTII cranks. Ultratorque cranks are both low profile and use exterior bearing bottom brackets. Properly installed, they are an upgrade to almost any other crank

maddog34

Campy also decided to make their chain rings more proprietary with that goofy BCD that certain ultra torques require...
what is your justification of that decision?

i think they were attempting to cut weight, AND proprietize their chain rings..... since all they had to do was keep the crank mounted screw boss 2 mm further inboard on the crank arm.......

and i'm not afflicted with mis-aimed feet, so ankle clearance is not an issue for me... from the looks of several hundred scuffed up cranks i've seen/owned, it is an issue for many others... including the previous owner of an ultra-torque crank set i have here in stock(paint worn off all the way to the center)........... so much for the campy having more ankle clearance, eh? it's all in how someone rides..... maybe she needs thinner socks? or to reset her shoe cleats/toe clips..... or specific yoga exercises... yah, that's the ticket! :-)

Bill Kapaun

IF I were desperate enough-
I'd just fill up all the grooves with weld.
Grind/machine back to the original length.
Mill interlocking "quarters".
Why all the grooves?

maddog34

yep.

well biked

I've got an Ultra Torque crankset that's about nine years old, it's not on one of my higher mileage bikes, but it does have several thousand miles on it and I've ridden it hard. The Hirth joint and the way it works is certainly different than any other thing I've ever seen on a bicycle, but my experience with it is that it's been entirely trouble-free. The Ultra Torque bearings have been very good, too, I've ridden this bike in all conditions and the bearings are still smooth and without problems, have not had to replace them. As for whether I would try and repair the Hirth joint if it were damaged, there's no way I would do that. That's a very critical interface, and could easily cause injury if it failed...the crankset's toast IMO. Good luck with whatever you decide.

xifias

Thanks for the extensive analysis.In fact why all that grooves were my question also,but in theory the more the grooves the bigger torque capacity the joint has.Also the ramps make the load distribution more even..maybe.

This crank allready had a split head bolt,that could end up to a serious injury if i werent be seated.
The exact cause is under question,maybe over tightening,maybe due to the joint,or improper facing of the bb+the inadequate engagement of the hirth..

But seeing it standing on the shelf all brand new and shining with not even one solution/discussion across the whole f.. internet feels more than frustrating.

Marcus_Ti

It could also be they changed the hirth-joint geometry from one year to another....not necessarily that your hardware was worn.

this is a question for gfk_velo.

nfmisso

Theoretically for torque capacity.

Same reason a Shimano freewheel removal tool is more reliable than a 2/4 prong Suntour.

maddog34

it's to help spread a load of a multi-directional and varying nature.

shear, flex, etc.

and helps shift the loading away from the bolt that pulls the faces together

ColnagoC40

To the OP, cheapest option will be a new chain ring set from Campy. Make sure you use Loctite on the crank bolt.

About the Hollowtech II that has no failures..... It will NEVER do the miles you can get on a Campy UT, not even close. Without getting into long detailed debates with non-technical folks, when it comes to mechanical engineering design, the Hollowtech design is pretty far away from best practices, and accepted principles.

Not a Shimano Hater, I ride both brands, BTW.

Bill Kapaun

IF you look at a Sun Tour tool, it's far from a 50:50 distribution. More like 25-33% depending on the version.
Apples to elephants.

4 equal width "quarters" would be much simpler and do the same job better.

Marcus_Ti

Yea...those Hollowtech cranks never failed...LOL.

ThermionicScott 

Signal boost to @gfk_velo.

gfk_velo

Nothing to be done at a cost lower than a new crankset, unfortunately.

It could be repaired by a machine shop with the right competencies of course - but recutting the Hirth joint would give you (amongst other problems) and interesting work-holding conumdrum with the crank attached.

For sure there are way around all of that but the accuracy required to give properly concentric bearings would be very expensive to attain.

maddog34

and ultra torque campy cranks are immune to failures, right?

see OP.

and any number of people searching for replacement retainer clips, wave washers, bearings, and shells.

failures are a part of riding at the limit.... and also a result of bad wrenching practices.

one must also consider the NUMBERS of shimano components in use, and the much lower number of Campy users.... that is a big part of the compared numbers of failures.

maybe campy owners are slower and weaker? ;-)

rm -rf

It's hard to see in the photo, can you post just the old crankset joint?

I don't see how a loose joint could wear down the teeth so evenly, since the force is clockwise on the chainring, looking from the drive side. What made the back side of the teeth so symmetrical?

Or, maybe the teeth are worn more on one side, and it's an illusion in the photo. A loose joint would make a noise on every pedal stroke! I'm surprised they rode it for that long without the bolt coming completely loose.

Is this an older design, or even a fake?

maddog34

and ultra torque campy cranks are immune to failures, right?

see OP.

and any number of people searching for replacement circlips, wave washers bearings, and shells.

failures are a part of riding at the limit.... and also a result bad wrenching practices.

maybe campy owners are slow and weak? ;-)

ColnagoC40

If correctly installed on a properly designed frame with CULT bearings, yes, absolutely.

sweeks

This^^. The piece on the left doesn't look worn, just different. If it were worn, I'd expect the wear to be at least a bit uneven and some sharp edges where the metal has been "mushed" out of position.
Steve

EDIT: Look at all the different Hirth joint configurations here: https://www.google.com/search?q=hirt...C6VQL2BaOS9CM: