Tuesday, September 14, 2021

American to European Bottom Bracket Adapters Aren't as Turnkey as I hoped! - Bicycle Crank Upgrade

When I bought my Huffy Rock Trail bike at a rummage sale few years ago, I admired it for having a one-piece crank.  Metallurgically speaking, I thought it was really cool to have the entire crank made from one forged piece of steel opposed to three separate pieces screwed together.  The reality is, this style of crank is inferior to the cartridge style bottom brackets that come standard on most modern bikes of adequate quality.  I wasn't convinced until recently when the bearing assembly started failing on me, and then kept failing after I repaired it 3 times in less than 2 years.

The first time it failed, one of the bearing cups cracked, resulting in a total seizing of the crank, as the bearings got lost inside the bottom bracket shell, and the crank went off axis.

It appeared that I ride this bike far too hard for this equipment to handle.  By comparison, my main bike with the cartridge bearings lasted 10 years and tens of thousands of miles before I had to change its bottom bracket.  Me still not being convinced, I bought a new bearing assembly to fix the one-piece crank.

Within weeks, possibly due to me tightening it too hard, one of the cones became pitted.  I noticed it because the crank would audibly click at the same point every revolution I pedaled.  I disassembled the crank again and replaced the pitted cone.  Months went by without error, until recently when the crank started becoming loose.  I tried tightening the cone and the nut to secure it, but it would keep coming loose to the point where the nut would start falling off.  Upon disassembly, it was evident one of the bearing cages split, and the bearings were no longer supporting the drive side adequately.

At this point I'd just about had it with the one-piece crank, so I bought one of those adapter kits to fit a cartridge bottom bracket in its place.

One problem, my bottom bracket shell contains protruding pieces of tubing that interfere with the adapter's installation!  The first half of the problem is that the bottom bracket cartridge is larger diameter than the old one-piece crank, and since the nice people at Huffy left barely enough clearance for the original one, I would have to file down that chunk of downtube that's in the way.  Second: the adapter cups are slightly longer than OPC bearing cups.  Again, the nice people at Huffy left barely enough room for those too, with the chainstay protrusions blocking me from inserting the cups all the way.  I wanted to use a die grinder to remove all the excess metal, but didn't have one on hand.

I instead used a file for the downtube part, but not being able to get close enough for the chainstays, I filed down the adapter cups instead.

Here I am removing a chunk from each adapter cup to clear the chainstay interference.  Now, I get the feeling that most bikes with one-piece cranks don't have chunks of tubing protruding into the bottom bracket shell.  I think at Huffy they were trying to save money by making the BB shell from a stamping, which could thereby have holes pre-punched for each connecting tube, rather than having to actually notch each tube.  I can tell the BB shell was stamped because there's seam on the back indicating it was rolled into a cylinder from a flat piece.

Anyways, all the adapter parts ended up fitting, but wait... why is my crank not going on correctly?  For some reason or another, the adapter cups were designed with the threaded holes recessed below the flange.  Perhaps this is to ensure the spacing would be correct for the cartridge... or whatever.  My crank, which was one of those cheap ones where all 3 chainrings are permanently welded to each other, had these 4 tabs on the inside of the granny gear.  What these tabs are for I have no clue, but it might be to prevent the chain from getting lost forever if it falls off on that side.  When I tightened the crank on, the tabs were scraping on the adapter flange.  I took it off and ground them down to make some clearance, but ended up having to slice them all the way off with a cutoff disk.  This might not have happened if I vied for a better crank where the chainrings are removable.... but it did, a nearly useless feature of the crank nearly prevented me from being able to install it.

In the end, I got what I wanted, though it took a few extra hours of filing and grinding to do so.  I am actually quite impressed with the results!  Performance wise, this crank has longer arms than the old one-piece crank, and I can definitely feel the difference.  I no longer have to work twice as hard to go the same distance.  This should've been obvious to me, that a longer crank would be preferred given my height.  It also now has nicer pedals. Only thing else I had to do was adjust the front derailleur to shift three gears instead of two with the old crank.

The moral of the story is, if you're trying to upgrade to a 3-piece crank, check first that the bottom bracket shell doesn't have frame tubing chunks that would interfere.  Otherwise, prepare for some intense modifications!  Also make sure your new crank isn't going to rub on the adapter.

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