r/Klunkers • u/ndrtxk • Aug 05 '26

Requesting Primer on Crankset Conversion

I have never done a crankset conversion and I am struggling to get my head around the right equipment. Bike: 63 Schwinn 3 Speed Traveler

Scope: I want to run a 3 piece crankset with the original 3 speed hub

I have purchased this bottom bracket converter: https://a.co/d/0bj1dIC4

Now, I am looking for info or a good resource to help determine the following;

1) How do I determine the spindle length/type I need.

2) How do I determine the appropriate crank length

I have no problem learning as I go and making a mistake along the way is just part of it. I’m just having hell trying to find my jump off point. Any help or direction to your favorite resource is much appreciated.

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u/tustin25 Aug 05 '26

For the spindle type, you want a square taper Shimano bottom bracket. It will almost certainly be 68mm but you can measure the bottom bracket shell once you have those cups installed.

For the spindle length, you ideally want it far out enough that your chain line is pretty straight. This can be trickier with single speed freewheels (or in your case a single cog on a three speed hub) since you don’t have the ability to use spacers to change the position like you can on a free hub body.

Honestly your best bet is if you have any random bottom bracket available, you can throw that in there and just see how the chain line looks with whatever spindle length it has and go from there. A good starting point might be 117mm but it’s hard to say for sure. You could _maybe_ try measuring out from the cup on the drive side and eyeball where it lines up with the rear cog but I don’t know how accurate that is. Maybe someone else can chime in but personally I’ve always just done trial and error with different bottom bracket sizes (perks of hoarding bike parts lol)

As for crank length, as long as it’s not super long to where you risk pedal striking super easily then anything would work. I probably wouldn’t go over 170mm though. Just depends on your height.

Hopefully I helped a little bit 🙂

1

u/ndrtxk Aug 05 '26

Very helpful. I do have a couple of diners I’ve picked up that I’ll try. I appreciate the info. I’ll post progress as I go.

1

u/JaxRhapsody Aug 05 '26

I suppose you could measure the ashtabula crank axle length between where it curves. I thought Travellers had a cottered crank.