[bigbossman]

I have an older entry level Univega Sport Touring tandem. The left rear stoker (non-drive) crank arm fits over a square taper spindle. The hole in the crank arm has rounded shoulders, causing the crank arm to be out of alignment with and forward of the drive side crank arm - not perfectly 180' opposed.

The crank arm is a press fit into the chain ring that couples it via the chain with the captains chain ring, so I cannot replace the arm without replacing the chain ring as well. I was thinking maybe a right side spider arm and single chain ring (BMX crank?), but the pedal thread wouldn't be right.

Can anyone offer a fix/solution/suggestion for this problem? does anyone have a spare 170mm tandem left crank arm/chain ring assembly they can part with, or perhaps a left side set?

Regards,

John D.

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[galen_52657]

John,

Look on Ebay. There are pleny of used tandem cranksets for sale.

[TandemGeek]

Can anyone offer a fix/solution/suggestion for this problem? does anyone have a spare 170mm tandem left crank arm/chain ring assembly they can part with, or perhaps a left side set?

You have three options:

1. Find a used one as you have requested.

2. Buy just a Sugino XD left-hand crank for about $32 - $40 through any one of the tandem speciality dealers, e.g., Gear-to-Go Tandems (http://www.gtgtandems.com/parts/cranks.html) or from any shop that can sell out of the Quality Bicycle Parts (QBP) Special Order Catalog as they offer the Suguino cranks, ala carte.

3. Use any square-taper right side crank with the correct bolt pattern needed for the size chain ring you'll need. If you're using inexpensive platform pedals, just install a right hand pedal with red loctite. If you're using better pedals, have your LBS or a machine shop install a left-hand threaded 9/16" x 20 TPI heli-coil.

[bigbossman]

Guys,

Thanks for the excellent advice. I am using "better" pedals, so I might just buy the replacement crank that was suggested.

Here's a follow-on question - keeping in mind that the stoker is a 10 year old girl, is this something I should be overly concerned about, or should I just let it ride for a while and see if it worsens?

John D.

[TandemGeek]

Here's a follow-on question - keeping in mind that the stoker is a 10 year old girl, is this something I should be overly concerned about, or should I just let it ride for a while and see if it worsens?.

Not knowing how often you ride, if it is was me, I'd probably try to mend the crank with some JB Weld or some other epoxy, noting that the bottom bracket spindle is probably buggered up too. At the same time, I'd continue my search for a cheap replacement crank knowing that the fix was temporary.

[galen_52657]

Now this is a jury rig....

But you could remove the crank, shim the spindle with some stips of aluminum can, re-install the crank and torque the crank bolt down a little extra to deform the shims to take up the slack.

[DocF]

Not knowing how often you ride, if it is was me, I'd probably try to mend the crank with some JB Weld or some other epoxy, noting that the bottom bracket spindle is probably buggered up too. At the same time, I'd continue my search for a cheap replacement crank knowing that the fix was temporary.
JB Weld, the slow drying kind, is wonderfully strong stuff. I've even used it to repair heads on a race car and had it work. If you feel the bottom bracket spindle is not trashed, you can carefully wrap a single layer of plastic wrap on it and then butter in the JB weld on the crank. Tighten the bolt, wait at least 24 hours before using after this repair.

Good luck,
Doc

[bigbossman]

JB Weld, the slow drying kind, is wonderfully strong stuff. I've even used it to repair heads on a race car and had it work. If you feel the bottom bracket spindle is not trashed, you can carefully wrap a single layer of plastic wrap on it and then butter in the JB weld on the crank. Tighten the bolt, wait at least 24 hours before using after this repair.

Good luck,
Doc

Excellent suggestion, as is the pointer to the source for new (and inexpensive!) left side cranks.

I appreciate the help given to a tandem newbie (me). I just bought this used bike last week for my wife and daughter, who had been riding metric centuries on a rented KHS tank. I figured that for $200, this was going to be cheaper than the $35/day rental bite... :)

I'm no stranger to checking out bikes, but this is my first tandem and I missed the off-kilter crank arm when I inspected it. Other than that flaw, it seems that it was lightly used. All it needed was new brake pads and grips, and they rode it on a metric century last Saturday with no issues.

I also replaced the 2" knobbies with 1.5" slicks, replaced the drive side 48/38/28 crank with a 50/38/24 one that I had laying about, and changed the rear cassette from 11-28 to 13-30. That seemed to give them some more high and low end at the same time.

Now, can anyone recommend a decent, comfortable saddle for the 10 year old? The LBS suggested a good women's saddle with a narrow front and a quick taper to the seat. Does anyone have experience with this issue?

Thanks again!!

John D.