Sorry folks,
@Athena &
@rich c; the Izip Mtn. Trailz came with a non-adjustable suspension fork with some covering material at the top part of the fork just below the crown.
Try holding the stem and fork area at the crown and rock the fork back & forth. If there's movement, then either the headset is loose and needs adjustment or the 2 bearing sets (generally found in a retainer ring) are worn. Or possibly both. Heavy use without proper maintenance or adjustments of the headset can wear the bearings rapidly as can riding with big loads or over roads with lots of potholes.
If I remember correctly, this bike has a threaded headset, with an upper & lower set of bearings. The upper set of bearings will have 2 nuts present. The lower one is the race that the upper bearings run in, the upper is an adjustable lockring. If what you're experiencing is a little 'shimmy' that sounds more like an adjustment issue with the possibility of bearings starting to wear.
This is a simple adjustment that you can do yourself with a pair of thinner adjustable wrenches if you don't have a
headset wrench.
- With the handlebars still in place loosen the upper lockring nut so that it's easy to get the headset wrench or a thin adjustable wrench on the lower nut. You will want the headset to rotate freely without binding from being too tight or knocking from being too loose.
- Once you have the lower nut where everything feels smooth, give it a final check by holding onto the forks near the crown (this is critical so that normal play with a suspension fork doesn't interefere) and rocking them back & forth and checking that they swivel smoothly without little hops, grinding or sticky points.
- Finally, with your thin wrench or headset wrench on the lower nut, tighten the upper locknut while keeping the lower nut from moving.
- Check your adjustment one more time to make sure you didn't accidentally over tighten the lower nut. It might take a couple of tries to get the headset exactly how you want but it's a fast process.
Here's a short video that makes the adjustment process easy to understand:
After getting the headset adjusted properly, if there's still some grinding it may be time to replace the bearings and install some fresh grease on the races. This might be something you'd want a bike shop to do.
If on the other hand, you can hold the fork crown still and get the arms of the fork to move back and forth, that's a very serious issue and you should stop riding the bike immediately until you can get it to a shop. That means there's cracks from metal fatigue starting to form which could result in a bad accident from a sudden failure of the fork.
Adjustments are not costly at a shop and if it's bearings, there's a little more cost but not excessive. Even a replacement suspension fork similar to this (
Zoom brand) run about $50/$60 and a rigid fork might be as little as $30.
No matter what you diagnose, don't delay getting it fixed; even a loose headset can result in damage to the forks.