Cottered Crank Conversion

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wheelhorseman

wheelhorseman

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Working on the Sears tryke today trying to convert over to a square taper. Can I simply swap out the spindle to do this? Heres what I can tell you. One cup is pressed in the frame and threads are different than a Wally mtn. bike. The covtter axle is longer on one side where the Wally axle is equal. So will a square taper axle work if I can come up with the right size?
7a8aqaja.jpg
I tried the Wally axle and it has too much side play but otherwise I think would work.

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As an academic exercise, the switch from a heavy steel cottered crankset to a lightweight aluminum tapered one is quite do-able. We achieved this very conversion back in December on a classroom road bike build. The bad news...we had access to a large cache of parts and nearly 1000 donor bikes from which to draw those perfect pieces for the job.

It isn't unusual for a spindle to be longer on the drive-side to allow space for the ring and chain. Your replacement parts need to account for this, as well. I would not recommend that you "mix-n-match" the spindle, bearings, and cups. In a perfect application, the only part used from the original bottom bracket would be the shell itself. Everything else gets swapped.
 
guqa7e4e.jpg
Heres a pic of what I am dealing with. Drive dide cup screws in. Unsure about other side tho. As you can see it has a large ring nut but I dont know if cup is screwed in or not. If its pressed in why the nut?
qamy2atu.jpg


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AH! Here's a little primer on three-piece bottom brackets...

The drive-side cup is considered a "fixed cup" and is usually reverse threaded. When properly installed, that cup gets cinched down tightly until its shoulder sits firmly against the BB shell. The other cup is "adjustable" and can be threaded in or out until a snug, but smooth-running setting is achieved. The large lock ring is used to hold that setting once a favorable adjustment is made--it prevents the cup from loosening on its own. The face of the cup will either have wrench flats, or more likely in your case, small round holes for a pin spanner. These are provided to make the necessary adjustments in or out, and to prevent that setting being disturbed while the lock ring is tightened. That cup isn't pressed-in...with the appropriate pin spanner and lots of lube, it should back right out.

Depending on how loose that Walmart spindle fits, you just might be able to take up the slack by tightening the adjustable cup. But, always begin by installing the fixed cup first...and completely.
 
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Thank you Rusty. That cup does have holes in its face so it must be screwed in. Iwill bust it loose and try adjusting to the Wally spindle but its pretty slack. Look at the pic. Which way does that cup screw in when bike is upright?

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The adjustable cup is invariably standard right-hand thread--the same threads the lock ring rides on. You may be tempted to grab these with chan-nel-lock pliers or other inappropriate tool...don't. The right tool for the job looks like this:

32655_Pin_Spanner_MG_9646_1.jpg

Good luck!
 
wheelhorseman said:
Thank you Rusty. That cup does have holes in its face so it must be screwed in. Iwill bust it loose and try adjusting to the Wally spindle but its pretty slack. Look at the pic. Which way does that cup screw in when bike is upright?

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Click to expand...
The opposite of the other one...

I have done cottered to square taper conversions too and they usually seem to work out pretty good.

Luke.
 
I am soaking it and will try to turn it tomo. UPDATE Was able to get the cup out and YES the Wally stuff is a perfect match but the cotter axle has a wider bearing spacing so I will need to find a proper width spindle is all. What about using a cartridge bb from ebay? How do I know what fits?

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Where are you? I have access to piles of BB cups from Wally bikes in Athens GA.

Edit: Sorry, did you say the BB shell threads in the frame are not compatible with new cups? If that's the case then a cartridge won't work. But that would be weird.

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I've done a couple of these conversions but always with a sealed cartridge BB. I personally would not use an adjustable cup bb except for an all-original restoration.
 
Yes they are compatible from wally junk.BUT shells are 73mm wide. Found that out by watching bikemanforu on you tube. And I am not far from Athens. I think going cartridge is my easiest and cheapest way to go rather than pieceing junk.
The bike is a Freespirit Ted Williams is all I know.
y9y4a3uj.jpg

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73mm english-threaded cartridge BBs are super common and pretty cheap. You just need to determine what spindle you'll need for your crank to achieve the desired chainline with your bike's rear-end.

Here's an example; not sure if your crank set-up will take a 110mm spindle, but that unit will fit the frame perfectly. I the spindle you were test-fitting is known to play well with the rest of the drivetrain, just measure that in metric and select your BB accordingly. A cottered crank-equipped Sears bike will likely be Austrian made, which is why the Wallyworld BB cups thread into it properly. something French or Italian or from the wrong factory/era in Britain, and you'd be SOL.
 
The Austrian sears bikes have a Swiss bottom bracket, the pitch and threads are the same as a french bottom bracket but the Swiss fixed cup is left hand thread. I imagine if a WM bottom bracket fits then the frame must have a british/ISO thread like most modern bikes. Another good chart. http://sheldonbrown.com/cribsheet-bottombrackets.html
I hate dealing with weird and obsolete threads and sizes.
 
Good point... early Puch-built Sears bikes may have Swiss BB shells; later ones might be the more standard BSC/"English" threads. To make matters worse, an English cup is close enough to the size to seemingly fit the Swiss shell. Measure the shell from side to side... if it is, indeed, 73mm, then it's almost certainly English-threaded.

Just curious: are there any decals on the trike that indicate where it was made?
 
I went through this last year with a Kahlkoff frame. I got the Cottered crak off but I had swiss cups. your standard spindle won't fit in it. You need a shimano spindle made for Italian bikes. You may be better off using a threadless bb. Velo Orange makes a good one, sunlite makes one too, but I had bad luck with mine always coming loose. Could have been solved with some lock tite.
 
Thxcuz said:
I went through this last year with a Kahlkoff frame. I got the Cottered crak off but I had swiss cups. your standard spindle won't fit in it. You need a shimano spindle made for Italian bikes. You may be better off using a threadless bb. Velo Orange makes a good one, sunlite makes one too, but I had bad luck with mine always coming loose. Could have been solved with some lock tite.
Click to expand...


There's actually a surprisingly good assortment of Shimano 70mm spindle lengths on Ebay right now. ;-)
 
I must have misread the post. Sorry for my misinformation. There's nothing like oddball parts to keep life interesting.
 

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