GRAN PREMIO CRANKS SELECTION

Most, if not all, components selected for the bicycle were picked because they had little or no value for resale.  A blemish might be a reason to de-value a component.  Cottered cranks, generally, were less valuable than tapered alloy ones.  Additionally, the cottered set would add to the vintage appearance of the finished bicycle.  That said, the vintage appeal of the cottered set would be compromised with the installation of modern mountain bike clip-in pedals.  At any rate...

Selecting a crank set was an issue and, after trying this and that, a Stronglight was finally chosen.  Though such cranks might never have been installed by Legnano, I did have several steel cottered Stronglight sets on hand.  Most were in nice shape, however, a set or two did offer a blemish or two that would significantly reduce the crank's value to someone else.  The blemishes, I might add did not stand out.  I did want my vintage Legnano to look good when it was completed.

Installing the cranks proved to be a minor challenge.  The spindle had to be sanded as smooth as I could get it.  The spindle bore in the crank arms had to be carefully cleaned up so that the Stronglight cranks would fit.  Once installed and cotter pinned into place, I discovered that the crank ring arms were bent about one millimetre in, at one point or another.  During rotation, one of the crank ring bolt ends was scraping the drive side chain stay.  Fortunately, repair would prove to be very simple requiring few, if any, special tools.

The first thing to do when straightening out a crank or crank rings is to determine what is bent, where it is bent and how much it is bent.  To determine the degree of damage to the cranks, I removed the ring sets and measured the distance of each crank arm to the same spot on the frame set.  By doing so, it was easy to see which arm, or arms in this case, were to be bent to realign the cranks and rings.  As it turned out, two arms had to be bent out about 1mm each to get everything nice and straight again.

Bending crank rings is a fairly simple job, be they steel or alloy.  The trick is to bend them just enough to ensure that the rings go round and round without wobbling.  Any wobble will negatively impact shifting precision, which will most likely reduce the quality of the ride of the bike.  This does not mean that it will not feel as good when being ridden.  It simply means that the nuisance of sloppy shifts will detract from the pleasure of the ride experience.  Might as well do the job properly now and save yourself the grief later on.  Once again, straightening the crank rings is a simple task, requiring no special tools and very little training.

Bending the crank arms cannot be achieved, with the cranks mounted on the bicycle.  Bent crank arms might well mean, replace them.  If you can bend them back into alignment, the arms will have to be held in a vice.  It will take considerable force to achieve results.  Safety issues will arise.  Fortunately, it is rare that the arms themselves get bent.  Usually, it is just the spider and/or crank rings that suffer from being out of alignment.  Both rings and spider arms can be adjusted while the cranks are mounted on the bicycle.

Bending the crank spiders back into place means that I will be using a tool to pry (bend) the arms back into place.  To apply enough pressure to achieve the bending action, the prying tool will have to pry against the bike and the spider arm at the same time.  DO NOT EVER PLACE THE PRYING TOOL AGAINST A FRAME TUBE!  Frame tubing, particularly on high end road bikes, can be very thin.  Prying against the thin tubing will most likely result in a dent.  Not the best way to restore a vintage road bicycle.

It is, however, OK to pry against the bottom bracket.  Protect the metal of the bracket with a soft cloth, or something to prevent marring the bottom bracket.  The picture does not show any padding but it is wise to ensure that some is in place.  It might be a good idea to enlist the services of a friend to assist with this little task.  An extra pair of hands will make this job much easier to implement.

Work in very small increments, when attempting to bend the rings or spiders.  Bend a little, and measure a lot, until each of the spider arms measure the same distance, from the point of reference on the frame set.  Once satisfied that the spider arms run true, attention can shift to the ring sets.

Once you are sure that the crank arms and spiders are running true, it is time to check the trueness of the rings themselves.  It would do little good to straighten out the spider arms, only to mount a warped set of rings back into place.

With the rings mounted, and following the same procedure used to measure the spider arms, check distance, from several different locations on the big crank ring to the point of reference on the frame set.  If the spider arms were bent, then it is quite likely that the rings themselves would be bent.  Just measure and bend - the ring only! - until the big ring runs dead true.  Now turn your attention to the smaller ring(s).

Though I do not have the proper tool for bending crank rings, the tool is available through a number of different sources.  Though I have never felt the need to purchase the tool, others might feel differently.  The point is, the correct tool for the task at hand is available, if you choose to seek it out.

It does not take long to straighten out a set of crank rings and it is a fairly simple thing to do.  Steel spiders are usually easy to straighten also.  However, when the crank set in question is alloy, be CAREFUL!!!  And keep in mind that many alloy crank sets come fitted with one or more steel rings.  And some steel crank sets come fitted with alloy rings.  Pay attention to what you are working with or you might end up paying to purchase another one.

Alloy is NOT nearly as forgiving, to distortion pressure, as is steel.  Alloy will form cracks, under distortion pressures, and those cracks might well result in complete failure of the component during operation.  Complete failure being defined as "snap in half".  Imagine hammering up a hill and "snap", the drive side crank breaks off, with your full weight on it?  Crash and probably a bad one at that.  With this in mind, I personally, do not straighten out alloy crank or spider arms.  The risk of catastrophic failure of the compromised part is just too great.  Alloy crank rings, however, are another story.  I have no problem moving an alloy ring, in or out, providing that the rings are not too bent to begin with.

Too bent?  More than a couple of millimetres would would qualify as too bent in my books.  That said, keep the following in mind.  If a ring is bent IN 2mm at one point, and bent OUT 2mm at another point, the out of true measurement will be 4mm.  By repairing each, bending in the appropriate direction, you are actually not distorting any metal more than the mentioned 2mm max.  But the four millimetre wobble will be reduced to zero, or very close to it.  This is all just my rule of thumb.

While you are doing all of the above, keep in mind that what ever bent the component, might well have damaged a sprocket tooth or teeth.  Have a look at each tooth on the ring to ensure that none are bent or broken off.  A bent tooth, or teeth, will negatively impact shifting and drive operation.  It a tooth or teeth are bent, and not the 2mm allowed for the rings, you might want to just think about finding a new or at least better ring.  Bent alloy ring teeth are almost certain to fail soon under operating conditions.

That about covers how to inspect for, measure, and repair minor damage to just about any vintage crank set, when running true is the concern.  Be careful to not over bend and be precise when measuring.  The results will certainly warrant the hour or so it took to ensure that your crank rings run true.

NEXT - GRAN PREMIO SHIFTING ISSUES