Can anyone tell me what this bolt is please

It looks like the kind of thing that would be relatively easy to fabricate. Find a bolt with the right pitch thread, and a smooth upper part to the shank. Stick a nut on the end of it, and weld it on. Then chop off the original hex head, leaving you with the same layout of hex head, threaded section adjacent to it, and smooth shank beyond. Lastly shape the required profile with a grinder.

It's a cotter-pin. They can be found fixing pedal cranks to the bottom-bracket shaft on older bicycles. Yours looks to be severely worn. The "C" shape is supposed to be a flat ground at a slight angle to the axis, the idea being that as it is tightened, the wedge shape jams firmly against a flat ground on the corresponding shaft. Also found securing the kick-start pedal on older motor-cycles, and anywhere a lever needs to be secured perpendicular to a shaft. If you're lucky yours may me a standard cycle size.

Not hard to get a bolt, remove its head and grind that shape into the plain shaft section

I've gone through enough of those over the years, on my Mercier. I'm surprised that one was removed by driving it out. When they get that distorted, sometimes you have to drill them out.

Paul

Richard

On 20/06/2020 02:19, John Rumm wrote: ...

Also, as it doesn't screw into any other part of the machine, you don't have to match the thread, just the shank diameter.

Surely on a cotter pin the diameter of the threaded end has to be thinner than the diameter of non threaded end to fit through the hole, to be subsequently tightened. In that picture the diameter of the threaded end looks to be much thicker than the non threaded end so what's to stop it simply pulling through any hole as its tightened ?

michael adams

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I'll bet it will be a standard imperial size. The shank diameter does not have to be too accurate because pulling back against the angled flat will tighten it. Actually I'm not convinced that it is particularly badly worn either, the circular region at the left is machined to take the cross member. As others have said, if you have "run out of threads" it may be sufficient to add a couple of washers.

Also, I'm not convinced about the instructions above. I think you just need to find a bolt with a long enough plain shank of the right diameter, cut off the head and a bit of the shank if necessary, and grind the shank to shape.

As others have said, it's a type of cotterpin.

You can make a replacement out of any suitable bolt with a plain shank and matching nut, simply by cutting off the original head and grinding the correct profile into the shank. [Not sure why John Rumm said to weld the nut on - that sounds completely wrong!]

Matching the thread to the original isn't necessary - because the new bolt's original nut will fit the new threads anyway.

The profile of the slot will depend on what it engages with. You say that the rests are secured to steel rods. If these are pure cylindrical rods with no notches or flats, the bit to grind out will be a portion of a circle to fit the radius of the rods. If the rest can be rotated around its support rod, this sounds like the most likely.

Yes, you're right. Bicycle crank cotterpins have the threaded bit smaller than the smallest bit of the shaft with the taper ground in. It's not a conventional cotterpin.

Yes, you are right concerning a cotter pin, but it has to be smaller at the thread end because the full diameter is obstructed by the flat on the shaft that the wedge has to engage with. However, I concede that the thing in the OP's post is not a bicycle type cotter pin as others have pointed out.

Incidentally bicycles no longer use cotter pins, instead the cranks are typically secured either to a tapered square section, or a spline system on the crank shaft. And you need a puller to separate them, a hammer is no longer any use!

Phil

A bicycle cotterpin locates in slot machined in the axle. This also positions the crank on the axle preventing it sliding in or out.So its necessary to first mount the crank on the axle and line up the hole before inserting the cotter pin.

With the bolt in the picture it looks as though this procedure must be reversed. So the bolt is inserted into the crank equivalent and when the holes lines up the axle is fed through this. If theres a sholder at one end of the axle this will prevent sliding along the axle in one direction but not in the other.

michael adams

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Cotterless cranks have threads inside the holes. A crank extractor threads into these which itself has a threaded hole in the centre. A hardened steel pin is screwed into this which then acts against the end of the axle thus forcing the crank off the axle. Or quite possibly instead this simply strips the thread from inside the crank. Which in the absence of an expensive specialist tool may then require the use of a cold chisel and/or crowbar, liberal amounts of heat from a gas torch, and quite possibly the use of a hammer.

michael adams

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A trapezoidal truncated pyramid like the original is probably a lot easier for an amateur like myself to approximate to with a grinder and will work nearly as well.

This can happen if the puller/extractor is not fully screwed in before attempting the extraction. Or possibly if someone has previously partly stripped the thread like that.

Phil

I was assuming from the OPs description of it as a "bolt", that the hex section shown in the photo was a fixed head, and not a nut[.

If it is indeed a nut on the original, its even simpler - omit welding it on! :-)

It has to be nut, to tension the bolt/pin so that it clamps onto the support bar.