Bish Bash Bosh Part 7: Teething Issues

In a previous post I overhauled the bottom bracket bearings, now it's time to change the worn original Campagnolo chainrings for new ones.  To start off with, the cranks I have are 2010 Campagnolo Athena Carbon models which are different from the later years.  They only made this groupset in this form for one year, as I was to find out what should have been a simple swap turned into something much more complex

The Problem

After six years of use I was starting to get some problems with my chainrings, occasionally shifting down into the small ring would cause chainsuck.  Usually this is caused by worn teeth, slowly the chain rollers wear into the teeth and they start to take on a profile similar to a shark's tooth.  This causes the position of the chain on the chainring to change over time which means that when shifting down, the chain will not detach from it and it gets driven into the chainstay.   Also after 6 years of mostly road riding it really was just time, otherwise I would wear the chain and other drivetrain components more quickly

However, one would reasonably assume a consumable part like a chainring would be easily replaceable.  Not so with Campagnolo, particularly as their bolt pattern is proprietary and not interchangeable with other brands.  Firstly Campagnolo decided to hide one bolt hole behind the crank arm and then they decided to offset it 2mm which makes it incompatible with every other chainring on the market.  Secondly, they changed the design of the bolts and inner chainrings a few years after my cranks were released.  Instead of the conventional two piece chainring bolts, now the inner chainring is threaded and the bolt screws directly into it which is actually kinda neat.   However I was not sure whether I could get away with just replacing the outer chainring which was worn and using the original bolts.



New Rings

So I ordered the chainrings, a pair of Stronglight CT2 rings which are meant for Campagnolo 11 speed cranksets. This is where the first problems started.  I tried using the old style bolts with the old chainring and this didn't work, there was too little thread engagement because the outer bolt sits too far out on the chainring as you can see in the picture below.  So then I ordered the Campagnolo new style chainring bolts FC-SR200.




The FC-SR200 chainring bolts can be seen on the left with the new style inner chainring which has a smaller threaded hole.  The older style bolts are on the right and you can see they are two piece. 



You might think that it would be pretty straightforward now to fit these, however it wasn't so simple.  You can see in the photo above that there is a pad on the underside of the crank arm where the fifth 112mm BCD offset bolt sits.  The thickness of this pad means that the chainring needs an offset cut into the chainring surface so it will sit flat.  The Stronglight one was not enough and it made the big ring distort when tightened down.  You can see in the photo below the gap made at the chainring holes when only this fifth bolt is tightened, it should be dead flat.



So what to do?  I milled down the pad until it sit nice and flat.



Now with the pad milled down both chainrings sit nice and flat on the crank.

  

One Little Snag...

Now that was sorted I thought that was it, job done.  Doing a test ride they seemed fine, except for one thing... The chain suck is even worse!  Even with a new chain the chain constantly gets sucked up by the small ring!  It happens when shifting down to the small ring, particularly when there is a bit of load on the chain.  The old chainrings only did this when they were worn after 6 years of use.  This is infuriating and it's made a dent in the bash plate of the frame.  Even if I try to always pedal lightly when shifting down which was what I normally do, it will still jam occasionally.  Although sometimes it is unavoidable, I will get caught needing to drop to a low gear and accelerate suddenly and it will likely jam.


Secondly the big ring sat too far inboard, it would rub on the big ring's shift pins when running small-small when the chain is at the greatest angle, again this never happened on the old chainrings.  I had to use 0.6mm spacers to space out the big ring to prevent this from happening.

I'm not sure how I can really fix this without changing out the chainring, I think the phasing of the teeth between the chainrings is off which causes the chain to jam.  One solution is to file the offending teeth back slightly however this is less than ideal.  The amount of modification I've had to do to even get these to fit is frustrating.  That's all for now, stay tuned for more.  Thanks for reading.




2 comments:

  1. I don't know how many miles you do, but even with dry road miles a set of rings are toast after 4-5000 miles and that's with regular chain swaps /rotations every 1000 miles. Time to bite the bullet and join the standardised world of SRAm and Shimano.

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    1. Yeah definitely! I'm already looking at moving to a Sram groupset at some point in the future. Although with the latest groupsets their chainrings are also proprietary!

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