I finished a build but had a problem I don't want to make again.

Steel frame Masi for touring, 105 9-speed drivetrain, including triple octalink crank, long cage derailleur, and dura-ace downtube shifters. Got a great deal on the parts but I put the cranks on what was suppose to be a compatible BB, but after the first ride realized something was wrong as the crank arms would repeatedly come lose. After tightening many times I since learned that I ruined the inside of the crank arms, where it is suppose to fit onto the BB, like a key. LBS fit a mountain crank to the BB and it fit.

Not sure how to complete the build? What are the downsides tu using a mountain crank, is it possible? Would like to not drop a lot of money as I have other bikes, and this bike was a project and would be used for infrequent, light touring and other rides.

Thoughts?

Thx

You will probably need both a new crank and bottom bracket. If your octalink crank was ruined, I'd expect the bb has suffered as well. You could go retro with Sugino XD and square taper bb or go with a Deore trekking crank with the new external bb. Edit- I see you were planning to use a regular 105 triple. If that gearing suits you, I think you can get new Tiagra with bb for under $100.

Not nitpicking but a question OP, do you know if your BB was octalink version or version 2? Seems unlikely to me even damaged that a mtb octalink crankset would work with a road bike octalink BB, just my thought though.

I got the idea he had forced a road octalink crank onto a mtn bb....

Seems kind of surprising that your crankset and BB wouldn't be obviously compatible or not but it begs the question if the crank set was already damaged when sold to you, or it was the wrong BB. Solution sounds like replacing with stock BB and new crank. If you don't care about branding and keeping it 105, then a cheap replacement might be a Vuelta USA crank set (around $35) and it takes a JIS square taper sealed BB. See Vueltausa.COM.

Not the lightest, but sturdy steel chainrings and inexpensive and if you had 105 in black, it might match colour.

Noonievut, I just installed a 6503 triple/BB. Mine doesn't and neither of my other two V1 Octalinks had this, but there maybe one narrow key spline that is fitted opposite the long part of the crank arm. This could be one way to incorrectly install the crankarms. There are two different V1 Octalink road BBs, one for a double and a wider 118 mm (or 118.5 mm, I don't remember) for the triple. I haven't dealt with a mountain bike octalink and can't comment from experiance, but I'd expect it to have a 73 mm body to match the BB shell.

A possible downside to using a mountain bike crank set would be the arc of the FD, which maybe engineered to match a 52T large chain ring. This can cause the chain to rub the cage in some gear combinations. You can use a Tiagra compact triple FD, which is often used for touring bike builds. Worth testing the current FD before blindly replacing.

Brad

Assuming the correct Octalink version was matched to the crank, it is possible to install the crank arms on the spindle without seating the splines by having the splines on the crank and the spindle meet end to end rather than mesh properly. If that is done and the bolt tightened well, the crank will work for a short time but eventually slip and tear up the crank's splines. The spindle is too hard to be damaged.

I have two 6503 cranks and always remove the outer ring of the self extractor so I can look inside to be sure they are assembled correctly.

I actually own the triple version of the BB, linked shockingly enough to a triple ultegra octalink ver 1 BB, the only difference between the two is the spindle length. Octalink Ver 2 comes in both 68 and 73 bodies for shells. I am still very confused by this thread though, when I misinstalled by octalink cranks all that happened was they both flopped down so the pedals were just above the ground and you couldn't crank.. I want to see pictures of these parts so we can determine if it's really a v1 and v2 mismatch or wtf actually happened.

I've been through this and it is indeed possible to install a V1 crankset (105, Ultegra or DA) on a V2 BB. Takes a lot of force but it can be done and the end result is a ruined crankset, which is softer than the BB. Bought a bike and the former owner had done it this way, found out the first time I test rode it. Had to toss the crankset and had no need for the BB so tossed that as well.

Good news is that Truvativ made a VERY nice triple crankset that mates nicely to the rest of the group and takes a 115 square spindle BB. They can be found on eBay or occasionally through places like Wheel & Sprocket in Milwaukee. Here's one that comes with a sealed BB and the price is very attractive: https://www.ebay.com/itm/TRUVATIV-Tou...item4173eedf2c

Pictures from me or the OP? Determine what the cause was for you or the OP?

If the crank arms both fell to the 6 o'clock position they were not installed as the splines on the BB have to engage the slots on the crank arm. Here's a link to show the difference between V1 and V2 Octalink BBs. Oddly there is no mention of a narrow key spline for either that I had read about. https://sheldonbrown.com/bbsize.html

Brad

Thanks for the info as always.
I knew what happened in my scenario, and now that the RC doctor has informed us, I think I know what happened with the OP too no pictures required

Disagree; the BB is steel and the cranks are ally. The BB is most likely fine.

Shame about the cranks. Naughty, for not finding out why it didn't fit nicer before cranking up the bolts.

Destroying fresh Ultegra gear makes Kimmo cross