Odd crankarm problem



Nukuhiva

Well-Known Member
Jul 14, 2004
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My daily beater is sick. The bike is a 1970's/early '80's (probably) issue KHS 10-speed, very comfortable, perfect size and geometry for commuting, so although the bike may be a cheapie, I'd like to keep it around. The cranks are slightly unusual insofar as they are held in place by cotter pins and they have a little ridge inside them, which slides into as keyway in the bottom bracket axle. The guy at the bike shop worth going to for vintage bikes says he's never seen one like that. The left crankarm has lost said ridge - eaten away by decades of being cranked, no doubt - and CANNOT be tightened by cotter pin alone. No matter how far you drive the pin in, no matter how tightly you screw it shut, it wiggles loose almost instantly. The right crankarm is fine, solid as a rock. The aforementioned guy at the bike shop says that's impossible, cotter pin should be enough. It's not. I've finally given up trying to fix what I have - too many failed attempts in too many different ways - and resigned myself to the fact that I will probably have to replace the entire bottom bracket plus crankarms, hoping I can find one that fits... This bike did seem to come with a host of components no one has ever heard of, the shifting system was rather unusual, too, didn't even bother trying to find replacement parts, just changed the whole thing. Anyone have any better ideas?
 

alfeng

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Jul 23, 2005
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I presume that you are using a NEW, replacement cotter & not trying to use a cotter pin which is no longer viable ...

  • I don't know what "ridge" you are referring to (post a pic, or two if you want to clarify ...)

If not, then you need a new cotter pin, you can either fabricate one (!) or simply buy one from HARRIS CYCLERY (it will seem to be over-priced AND you will have to pay shipping) ...

The makeshift alternative is to shim the cotter pin with some brass "ribbon" (go to your local HOBBY LOBBY or other hobby shop to buy the over-priced brass stock) to snug up the cotter pin which you are trying to use.

FYI. There is a 99.99% probability that you can use any BB which has an English threads ... English threaded BB shells were-and-are the norm for steel Japanese bikes ... just remember that the driveside cup on an English threaded BB has a left hand thread ...

  • In most instances, the cottered BB spindle can be replaced with a square taper spindle ... just remember that the spindle needs to be matched to the crank ...
  • most European cranks had ISO tapers whereas the rest (meaning the Japanese cranks) where typically JIS (but, the SunTour cranks which were typically ISO); but, the required spindle length could vary greatly

FWIW. As a replacement, I recommend that you just opt for either an FSA MegaExo (external bearing) crankset OR a Shimano crankset + Shimano cartridge bearing BB ... whatever you find on eBay which suits your wallet & aesthetic sensibilities.
 

Nukuhiva

Well-Known Member
Jul 14, 2004
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Hi and thanks! Yes, a new cotter pin was the first try, the first 4 tries, in fact..... Got to the point where I just broke a pin at the threads by tightening it that much. The 'ridge' (words will have to do, haven't got a digital camera) is just a square metal strip on the inside of the left crankarm, which slides into a square slot on the spindle, located (obviously) opposite the flat side where the cotter pin goes. Interestingly, only the left side has this, the right (chainring) side is just a round spindle with a flat spot for the cotter pin, and it's rock solid. I've tried shimming the pin - as well as the arm - with a variety of materials, at some point, I even drove part of a horseshoe nail (which is kinda square) into the spindle slot. That worked for about half an hour, then the nail just fell out. I took the crankset (Shimano FF System, Integer chainrings 52-39)off this morning, which was surprisingly easy despite stiff, cold fingers, and will try to find a new spindle. A cup remover tool is probably the one bike tool I do not have, but if it turns out that I have to replace the whole shebang, the extra $ 15 or so won't kill me.....
 

alfeng

Well-Known Member
Jul 23, 2005
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Originally Posted by Nukuhiva . ... A cup remover tool is probably the one bike tool I do not have, but if it turns out that I have to replace the whole shebang, the extra $ 15 or so won't kill me.....
You can just use a MEDIUM-to-LARGE (as in a non-industrial "Large") adjustable wrench to remove the fixed cup ...

If you are not trying to save the cup, cosmetically, then you can just use a pipe wrench ...

Use that $15 toward a Hollowtech II Cup tool or toward an Octalink/Isis/etc. Cartridge Cup tool.
 

daveryanwyoming

Well-Known Member
Oct 3, 2006
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Originally Posted by alfeng .


You can just use a MEDIUM-to-LARGE (as in a non-industrial "Large") adjustable wrench to remove the fixed cup ...

If you are not trying to save the cup, cosmetically, then you can just use a pipe wrench ...

Use that $15 toward a Hollowtech II Cup tool or toward an Octalink/Isis/etc. Cartridge Cup tool.
Yeah if the fixed cup flats are in good shape (not rounded) and your wrench is in good shape you can usually get the fixed cup off but if the cup is really stuck (not unusual on older bikes) it's not uncommon to bash knuckles when the wrench (or even good fixed cup tool) slips off the very slim edge of the fixed cup flats.

Personally my favorite old school fixed cup removal tool for stubborn fixed cups is a 5/8" machine bolt about an inch and a half to two inches long, a matching nut and some small OD washers. The late great Sheldon Brown describes the use of this tool nicely here: http://sheldonbrown.com/tooltips/bbcups.html I've used that method on both English and Italian fixed cups that were solid as a rock and I couldn't get them to budge with the normal fixed cup tool and with much less risk of bashed knuckles.

BTW, I second Alfeng's suggestion to just focus on getting the old fixed cup out and apply those funds to the tool you'll need to install the new bottom bracket.

-Dave
 

Pat Stowe

New Member
Jan 3, 2012
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Cotter pins come in several diameters, several, lengths and have several tapers or slopes on the "flat" side of the shaft. It is quite possible your cotters were mismatched (slightly) in the past, otr damaged from poor inatallation technique before you had the bike. The mech your're dealing with may not beas "expert" as he might be as cotter pins became scarce some time ago. It takes some traing experince, sprcialized tools, and a litlle luck to get em installed just right. (they have to be "pressed in" with a plier like tool and then secured with the nut to do it right. If it wre mine I'd update the cranks
 

dhk2

Well-Known Member
Aug 8, 2006
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Originally Posted by Nukuhiva .

My daily beater is sick. The bike is a 1970's/early '80's (probably) issue KHS 10-speed, very comfortable, perfect size and geometry for commuting, so although the bike may be a cheapie, I'd like to keep it around. The cranks are slightly unusual insofar as they are held in place by cotter pins and they have a little ridge inside them, which slides into as keyway in the bottom bracket axle. The guy at the bike shop worth going to for vintage bikes says he's never seen one like that. The left crankarm has lost said ridge - eaten away by decades of being cranked, no doubt - and CANNOT be tightened by cotter pin alone. No matter how far you drive the pin in, no matter how tightly you screw it shut, it wiggles loose almost instantly. The right crankarm is fine, solid as a rock. The aforementioned guy at the bike shop says that's impossible, cotter pin should be enough. It's not. I've finally given up trying to fix what I have - too many failed attempts in too many different ways - and resigned myself to the fact that I will probably have to replace the entire bottom bracket plus crankarms, hoping I can find one that fits... This bike did seem to come with a host of components no one has ever heard of, the shifting system was rather unusual, too, didn't even bother trying to find replacement parts, just changed the whole thing. Anyone have any better ideas?
Your left-hand crankarm sounds like a special design I've never seen. But if it uses a "ridge" on the arm which engages a keyway on the axle spindle, and the ridge is gone as you say, your problem seems obvious to me....the crankarm is "stripped". Don't know how the cotter pin is used on the left-side, but it's also obvious it isn't there to stop rotation of the joint. The guy at the LBS should have been able to figure this out.

You might be able to repair the crankarm by drilling/tapping for two or three set screws which engage the axle keyway, or by machining a companion keyway in the crankarm and then using a lock key. But for the cost, time, and chance of failure, I'd skip the repair options and get a new BB and crankset.