I am now forced to suspend the build for about a week, as I am waiting the delivery of parts and tools. In the meantime I am learning about cranks, cogs, BBs, and other things.
Originally Posted by
NormanF
Congratulations! The rear cog needs to be swapped out to an 11-36 and you’ll want a 20T for your granny gear to get a low. Since touring bikes tend to be heavily loaded and you may face steep climbs in mountain country, you’ll be thankful to be able to make short work of most steep inclines.
I believe 24T is the smallest cog that goes on a 74mm BCD. The factory crank is 26-26-46, and I have rehabbed that, but have an order in for a
new crankset that expands it up to 48 and down to 24. Hopefully will not mess up the front derailleur's operation.
Originally Posted by
saddlesores
"...In addition to the ramps and pins, modern chainrings designed for derailer use often have the teeth in the area adjacent to the ramps cut with shorter peaks than the other teeth, again to facilitate upshifts..."
https://www.sheldonbrown.com/images/ramps-pins.jpg
"...most newer rings have teeth that do not all look the same. While they are spaced at a consistent interval (to match your chain’s pitch), the heights and profiles can differ significantly. Depending on what is done to the teeth, the shaping can aid in shifting up-and-on-to the big ring, and also accurately dumping down to the small ring..."
https://www.slowtwitch.com/articles/...ks_intro_2.jpg
those rings don't look that bad, and a closer look at the cassette doesn't show that much wear either.
how 'bout just clean it all up, check the chain for wear, lube & ride.
https://cimg0.ibsrv.net/gimg/bikefor...e69aae9ac.jpeg
That was super helpful. I was amazed to learn about the various details and nuances that go into crank manufacturing and what it takes to combine them for smooth transition of the chain.
Originally Posted by
andrewclaus
I also think the middle ring looks fine. The "missing teeth" are designed that way. There seems to be very little normal wear on it.
And I agree that if the BB spindle rotates freely without play, no need to pull it. Cranks must be pulled to check it correctly, so you haven't wasted any effort. If I were heading off on a year-long expedition, I'd want a new one in there. Those are very robust units. Typical MTBF (mean time between failures) for me is over 20K miles. Judging from the lack of wear on the chainrings, there may be fewer than 5K miles on it.
Check the specs on the rear derailleur before you change the gear ratio by more than a couple of teeth. Here's a guide:
https://www.cyclecycle.info/bicycle-...ar-derailleurs
I have an order in for a new 11-30T cassette and hope the rear derailleur will operate the same. If everything operates well I will end up having 21-116 gear inches (the stock setup is 25-112" and I thought I can improve on that a tiny little bit, hopefully without having the replace the derrailleurs).