12/31/14 12:46 AM

We still have several bikes in our garage that use cranks with the old TA Cyclotouriste chainrings.The changing up to the big front ring is not as good as with modern chainrings, so I decided to see if fitting my own shift pins and lowering the height of the nearby teeth would improve matters.

I used some 1/8" diameter by 1/8" grip stainless steel pop rivets, countersunk the holes slightly on the outside face of the chainring to minimise the protrusion of the head of the pin after the pin shaft snaps off, and then filed down the height of the teeth immediately following each rivet.

The crank arm fits to the chainrings at about 10 o'clock in these photos. I've only tried the bike on the workstand so far with the new chainrings - there seems to be some improvement, but the real test will be out on the road tomorrow:

12/31/14 1:02 AM

Don't forget to update after real world test. Like!

12/31/14 6:40 AM

Not long ago, for aesthetic and practical reasons, I started using a crank (Sugino PX) with those TA rings. I haven't noticed much of an issue with the shifting, but it will be interesting to hear if this makes any kind of a real-world difference.

LET US KNOW!

12/31/14 7:00 AM

...if the pins had square, rather than rounded edges. It seems to me that you'd be better off with the rivets installed from the other side (without washers). Grind the heads down to 1mm in height or less and they should pick up the chain nicely.

12/31/14 11:51 AM

What I've found effective over the years (when shifting up to a larger ring was too slow to engage), was to bend every third tooth inward toward the non-drive side.
Even a half-millimeter, barely enough to visually discern, often made the difference between "shift" and "not shift" for a given adjustment of the hi-limit screw.

Somewhat similarly, when shifting "down" off of a triple's middle ring was sluggish (as when there was a big difference in chainring size from big to middle), the bending of every fifth tooth outward toward the big ring allowed the chain to disengage the middle ring and shift to the small ring. This was needed when the bb spindle chosen was on the short side, especially when the frame had an oversized seat tube that limited the front derailer's inward travel.

BTW, Shimano's earliest patented feature to enliven slugging shifting across chainrings was called "W-Cut" teeth, essentially pairs of shortened teeth positioned adjacent to each crankarm.

It can also be useful to bevel the tips of sprocket teeth in order to bias the chain's preference of moving to one side or the other of a particular sprocket. This can be done to the entire sprocket, while holding a file against a rotating chainring (which effectively moves the tips of every tooth away from the beveled side), or can be done strategically to every 3rd or 5th tooth, as when trying to get an old derailer to handle the shift outward to a wider freewheel's smallest cog.

Chainring teeth are easily bent using an adjustable wrench, and I've not broken a single tooth unintentionally. Cog teeth are best tuned using a 3/8" stone mounted in a dremel, to assist the shift off of the #2 cog toward the smallest cog.
Here, I hi-lighted a travel-increasing notch modification in red, but what is not easily seen is that I also had to bevel a few of the 2nd-smallest cog's teeth to assist with getting this very old (3-4-5-speed) derailer to shift the chain out to a 6th cog.
With six speeds now, the bike is a joy to ride even in these foothills!

1/1/15 12:07 PM

I imagine yours is probably Schwinn-branded, but it's still an Alvit. I replaced a lot of those with Suntour derailleurs back in the day...

1/4/15 12:06 AM

Well, the chainrings and front shifter got a good workout yesterday over about 90km of hills. The front shifting is definitely somewhat better than before, but unsure how much of this is due to the modifications and how much to a new chain and chainrings - the old chainrings were quite worn and starting to resemble fishhooks, and the old chain had more side-to-side flexibility than its new replacement.

1/5/15 12:57 PM

We did the W cut thing with a file on our Campy/Sugino chainrings years before Shimano ran with it commercially (In 1973 it was already a common practice)