Installing Cottered Crankset Misery

[Johnsqual]

Hello,

I am faced with the pretty miserable job of installing a cottered crankset.
Because it's a vintage project, I don't really have the option of replacing with
a modern set. The old spindle is worn out, and I've found a new one that is the correct length. Everything else is original (cotters, crank arms).

I've come across a couple of issues.

1) The crank arms are a tight fit on the new spindle. On the old one, they
could be slid on and off by hand. With the new ones, I've had to tap them
into place with a rubber mallet. Is this a problem for installing the cotters?
In particular, do the cranks need to be able to move about on the spindle in order to fit the cotters properly?

2) The pins only fit part way into the holes in the arms when attached to the spindle. The threaded part of the cotter does not stick out the other side of the arm before the cotter becomes stuck in the arm. On the old set up, the cotters fitted fully into the crank arm, with just a bit sticking out either end.

Can this be fixed by filing the pins? Or do I need a different size cotter? What does the size of the pins relate to? Is it just the diameter of the hole in the crank arm? Or does it also have to do with the flat part of the spindle that the cotter rests on?

Sorry, lots of questions, but the usual sources (Barnett Manual, Sheldon etc) are a bit vague on the subject and I've run out of info.

Cheers,

Johnny

 

[Robbied196]

Re:

I feel your pain

I've always found cottered cranks either go on really smoothly or are a complete pain! If the cranks are tight on the spindles that isn't going to help. If you look down the hole for the cotter, the spindle needs to be about the same angle as the chamfer on the cotter. That way you'll know its sliding in as far as possible. That's not going to be easy to adjust if they are tight.

If it looks right and your still not getting any thread then the cotters can be filed. Its also good to use a press to drive them in rather than a hammer or tightening the nut to pull them further through!!! A 'G' clamp will make a makeshift press. You can use a suitable sized nut, or a socket so that the threaded end of the cotter is able to pass through the hole as you tighten the clamp.

Remember if the cotter nut is facing up on one side of the crank, it needs to be facing down on the opposite side so the cranks stay parallel. You don't want to have to remove them again :facepalm:

I think the correct protocol is when the drive side arm faces forward the cotter nut should be at the bottom.

 

[FluffyChicken]

Re:

Have you read Sutherland 6th or before. There was quite a not in there from memory. I don't know much about them other than hitting them with a hammer as a young kid with my grandad.

 

[keithglos]

First the cranks must be a sliding fit on the axle, probably plating inside the hole. You should use whatever method you have for making them fit, I had an adjustable parallel reamer.
The original british cotter pin size was 3/8 inch probably the nearest you can get is 9.5mm, 9mm (the old French size is too small. Again if they are tight you should first make them fit the hole.

Cotter pins are fitted by trial and error, tap them in gently and file off until in far enough, taking care to maintain the angle of the slope.
The large manufacturer convention was for the cotter pin to go in downwards with the crank to the rear, although I can't see any reason, as long as they are in opposite directions.

If correctly fitted they should need no more than a firm hit with a hammer. The nuts are to hold them in, not for tightening the cotters.

Keith

This sounds a lot, but in the 50s would not take more than a few minutes.

 

[Johnsqual]

Re:

Brilliant replies, thanks for these gents.

It is a Belgian bike and so far it has had a bizarre and headache-inducing mix of French, British and 'what the hell, let's make it up as we go along' sizing standards :facepalm:

Cheers,

Johnny

 

[Martin Rattler]

Re:

Just to add my experience to what others have advised. I had similar problems fitting a chainset when I changed the BB spindle during my recent Gillot rebuild. The original spindle fitted the cranks nicely but was a little short; the used replacement spindle appeared to be slightly oversized, perhaps due to past abuse. As you have managed to drive yours on with a mallet I guess that your spindle is not so tight a fit as mine. I got mine to fit by dressing the ends of the spindle with a whetstone; as it is case hardened it would be too hard to file. After half an hour’s careful adjustment I had a nice sliding fit.

It my recent experience all cotter pins are oversized and need to filed to fit. As Keith advises you must do this carefully so as to maintain the angle of the flat and ensure that it remains flat does not become convex or concave so that it engages and sits well on the spindle flat; so you will need to use a vice. Be careful not to damage the threads. As Keith says the nuts are there to retain the pins, not to pull them down tight and you run the risk of shearing these off if you try to do this.

Rebuilding old bikes does demand some degree of hand fitting, much more that a modern machine; which is part of what makes it interesting. I suspect that many of the changes made in the design of componentry over the years came about largely so that bicycles could be assembled by semi-skilled labour on a production line rather than being any real improvement as such…but that’s just my opinion.

 

[Johnsqual]

Thanks again, that's really very helpful. I've had a go with a whetstone at another old spindle that was also a tight fit, and just a few minutes' work has already helped the fit, so I will have a go at the real spindle later.

Interesting comments about the value of certain 'improvements' to actual cyclists. Certainly aheadsets don't seem to offer much benefit in terms of performance or ease of adjustment, let alone aesthetics!