Bolts for Eccentric BB on Tandem
06-09-13, 01:42 PM
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Bolts for Eccentric BB on Tandem
Hi,
I have a tandem that has a pinch type eccentric BB. It has the same concept as this picture
As you can see, the bolt head goes inside the frame. My original bolts are now rusted and one broke off, so I am looking for replacements. I bought some M8 socket heads locally and the bolt head diameter is 13mm. The orignal's bolt heads were 12mm, which is not ISO standard. I do not know where I can get M8's that have a 12mm diameter head. Can anyone give me ideas?
Horace
I have a tandem that has a pinch type eccentric BB. It has the same concept as this picture
As you can see, the bolt head goes inside the frame. My original bolts are now rusted and one broke off, so I am looking for replacements. I bought some M8 socket heads locally and the bolt head diameter is 13mm. The orignal's bolt heads were 12mm, which is not ISO standard. I do not know where I can get M8's that have a 12mm diameter head. Can anyone give me ideas?
Horace
06-09-13, 02:17 PM
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Maybe take those standard screws (extra points for stainless) and a six-pack to a machinist and ask that he turn the heads down for you?
Get some longer screws and small-pattern washers and leave the heads protruding outside of the recesses? Button head screws might work without the washers.
Get some longer screws and small-pattern washers and leave the heads protruding outside of the recesses? Button head screws might work without the washers.
Last edited by dsbrantjr; 06-09-13 at 03:56 PM.
06-09-13, 05:44 PM
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Can you contact the frame/bike manufacturer? A few minutes with a bench grinder or belt sander will make 13 mm heads into 12 mm heads if you can't get the proper ones.
06-09-13, 06:04 PM
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that is only half a millimeter all the way around. Chuck the bolt in a drill and spin it against something abrasive. A file. or emery paper, the sidewalk, anything.
06-09-13, 06:06 PM
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Be sure to use plenty of stiff grease, or anti-seize when installing since the sides of the head will be very prone to rusting. Or you can paint the heads first and let cure before using, but I'd still grease them. (belt and suspenders)
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FB
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
06-09-13, 06:23 PM
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yea chucking up the bolt in the drill-motor and holding the spinning bolt head
against the bench grinder rotating stone is one way.. to take off that 1/2mm
against the bench grinder rotating stone is one way.. to take off that 1/2mm
06-09-13, 06:41 PM
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Yes, in theory, but not very likely, and annealing the head slightly won't hurt anything. If there's concern, keep a pan of water near the grinder, and cool the bolt from time to time if it shows any color at all. Straw color is fairly hot but OK, if it turns blue, you're overdoing it, and/or your stone is loaded up and needs to be dressed.
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FB
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
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06-09-13, 06:48 PM
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As FB noted, keeping a pan of water and/or a wet rag handy and cooling the work piece frequently prevents it. I've cut down Allen keys with a Dremel cut off wheel and, by cooling the part frequaently, never hurt the hardness.
If the new bolts are stainless steel, greasing or painting the ground edge to prevent rust will be unnecessary.
If the new bolts are stainless steel, greasing or painting the ground edge to prevent rust will be unnecessary.
06-09-13, 06:56 PM
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If you grind stainless and let it heat beyond a pale straw color, it will lose some stainless property there and may rust locally. (only the area that actually got to hot)
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Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
06-09-13, 10:03 PM
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Do you know who made that eccentric shell? Try contacting the tandem manufacturer or posting a photo of your eccentric shell on the tandem or framebuilders forum.
