Bad Crank set...
 

I am very new to cycling but have come to like it a lot..


I bought a used 1996 Cannondale H400.. bike is in what I think is pretty good shape for the year and price(30$).
Needs a little cosmetic work, a seat and a tire but rides pretty nice. biggest problem seems to be the on the Crank set a few teeth are damaged. bottom bracket feels smooth and no movement.


So, My question is.... How interchangeable are these cranksets..?? I can find a few with the same tooth configuration, but a lot more that are very close..


Feedback please...

Check first that the 'damaged' teeth are not actually shaped as ramps and gates to improve shifting. Ramped and gated teeth are often mistaken for damage by people unfamiliar with them.

I understand But, these are damaged...

Threaded frame , the whole crankset/BB Assembly set goes as one..

What is the type/extent of the damage? Does it interfere with riding the bike?


A few bent teeth can likely be straightened or burrs can be filed away. Some clear, well-lit and -focused photos will help us to advise you.


Cranksets can be changed but it may not be necessary. What is the tooth count of each of the chain rings?

yes, chain seems to jump a little under pressure..


I look at repairing and try to get a few pics this week end...

thanks for all the info but the original question..


Are Cranksets interchangeable ? Or do I need to look for something specific ??
What happens if I change the tooth count..??? Does this just change gear ratio's ??


Just trying to learn as well as fix..


Thanks,

Cranksets - and bottom brackets - come in several different versions. At least half a dozen.
Some will mount right up to your current BB, other will require a new BB too. Some may require a BB your frame can't take.
Easiest path is to look for one matching your current BB and tooth count.
The importance of tooth count depends.
Sometimes a bigger won't clear the chainstay.
Also, the curve of the front shifter is shaped to fit a certain range of tooth counts. Stray too far from the intended use and shifting may suffer.

Your original crankset should have been a Shimano Alivio, 24/32/42 teeth according to Bikepedia. Most likely square taper. If this is the case, pretty well any square taper mountain bike crank will fit.

You may not need to change the crank but just the chainrings. Count the number of bolts holding on the chainring and if needed the BCD (bolt circle diameter). Look for something that will fit. For example look at this chainring here and see if it will fit your cranks. You can increase or decrease the number of teeth within reason.

If you increase the number of teeth, you will most likely need to get a longer chain.

You should consider replacing the cassette or freewheel if you replace the chain.

This is NOT true; but if you stay within the Shimano cranksets which use square taper BBs, you will be okay.

Unlikely you will increase the length of your chain even if you go up a few teeth. Your chain is probably long enough, where you don't have to worry about it. Try the chain first, if there is a problem then get a new one. I am from the school where you don't replace anything until you have to. I guess it easy to spend other people's money.

I don't know where you are coming from please tell me one square taper mountain bike crank that won't fit this bike? Sure maybe the Campy one they sold thirty years ago. This is why I said "pretty well".

You can replace the crankset, but there's a little more to it than that.

The part/mechanism that connects a crankset to a frame is called the bottom bracket. Your crankset uses a square taper bottom bracket, the upside of which is that they're very common. The downside is that they were made with LOTS of different spindle (axle) lengths and you need to match a crankset to a bottom bracket with the right spindle length. So if you remove your crankset and throw a new one on there, it might not work even if your new crankset was designed for a square taper bottom bracket. Your new crankset might require a different spindle length.

To make it even more complicated, many older cranksets required asymmetric spindles that are longer on one side. Those generally aren't made anymore, so finding the right one for a given crankset can be problematic. (You can sometimes use a symmetric bottom bracket, with or without spacers to offset it.) There are even different taper sizes/types that can present compatibility issues.

So anyway, to make a long story short... Yes, you can replace the crankset, but if you want it to work, you've got lots of variables to sort out.

Some other alternatives: (1) You can buy a new crankset with the proper chainring combinations, along with a new bottom bracket that's properly sized for your new crankset. (2) If your current crankset's chainrings are bolted on and not riveted in place, you may be able to replace chainrings without replacing the whole crankset.

It depends on how different the tooth counts are. If they're within a couple of teeth and similar in range from big to small, it can likely work. You may need to reposition the derailleur on the seat tube, change your chain length, but those aren't a big deal. If your new crankset has significantly different chainring sizes, though, your front may not be able to handle the new gearing. If the difference in size between your new crankset's big and small rings is larger, you could potentially even exceed your rear derailleur's capacity.

...and yes, as you suggested, you'll likely feel the difference in gearing as well.

If you have a 44T big ring, and the chain is the correct length per Shimano's big-big recommendation, and you change to a 48T big ring, if you shift into the big-big combination, the RD will be destroyed, and likely take several DS spokes of the rear wheel..... quite a few $$$ there versus the cheap insurance of a properly measured chain length.

Shimano square taper MTB cranks are intended for 122mm BBs. There are many square taper MTB cranks intended for other lengths BBs, for example I have one that is designed for 110mm BBs; if installed with on a 122mm BB, the FD will not be able to reach far enough to shift into the big ring.