Need to change my Cannondale Mtn Bike to a straight up cruiser, but can,t find any handle bar stems with 11/8'' quill sizes.or longer than 6''

According to the manual:

If your bike has a "threadless" stem (fig. 6) your dealer may be able to change handlebar height by moving height adjustment spacers from below the stem to above the stem, or vice versa. Otherwise, you'll have to get a stem of different length or rise. Consult your dealer. Do not attempt to do this yourself, as it requires special knowledge.

If your bike has a "quill" stem (fig. 7) you can ask your dealer to adjust the handlebar height a bit by adjusting stem height. A quill stem has an etched or stamped mark on its shaft which designates the stem's "Minimum Insertion" or "Maximum Extension". This mark must not be visible above the headset.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiuyuupw8HZAhUEU98KHRk1BaoQFggpMAA&url=http%3A%2F%2Fkhsbicycles.com%2FPDF%2FKHS-Owners-Manual.pdf&usg=AOvVaw1LLFcErB5Fxs_LpkLUwB-K

loosen of the handle bar stem from the front forks and turn to square to the wheel then re-tension the bolt/s

Your bike appears to use an adjustable stem, which allows rotation to change the height/reach. Although such stems are a fairly new feature, they have been successfully used for several years. Apparently the one spec'd for your bike is not very sturdy. See the posts below from two people who had a similar problem. I suggest you complain to Walmart and ask for a fixed position replacement or a partial refund so you can choose your own stem.
My latest love hate bike the Genesis Onyx 29 beach cruiser
Genesis Onyx 29 Cruiser

I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881

the XC3 stem comes in a 1.5 in clamp designed to fit on cannondale headshox systems. The lefty fork you have may or may not be compatible, you would have to check your fork to see if it is the right size.

There is an XC3 SL conversion kit for lefty forks that are not the same size and includes the stem and steerer replacement.

Swapping stems is quite easy on the cannondale. Loosen the two bolts holding the stem to the steerer and undo the bolts holding the handlebars, remove stem and replace.

If none of this makes sense then I would strongly urge you too take the bike into your local bike shop, preferrably a cannondale dealer, and have them show you. It will take only a couple minutes and they can confirm compatibility.

i assume its a quill type stem if so loosen it so the wedge and stem are allowed to fit nicely inside the bike there is a bearing assembly to deal with after but they are pretty straight forward to install also there is a minimal insertion line on the stem ok

• It sounds like the quill insert is loose. The handle bar connects to the stem, the stem connects to the quill, the quill connects to the steerer tube.
  
• while sitting on the bike, tighten the quill adjustment bolt a half turn at a time until the handlebars turn instantly with the front wheel.
  

The stem can only raised safely within the steerer tube end to a line etched on its quill. There are stem extenders or even fixed-angle higher stems.

The sccret to getting a quill stem to move is to loosen the center (vertical bolt a few turns and then rap it down with a mallet to unseat the expander wedge inside the steerer tube.

It's possible your frame is sized improperly for you and your preferred riding position.

I would recommend you go to a real Bicycle Shop for those assessments.

If your bike is older it might have a quill stem.To raise this you have to undo the allen key headed bolt situated where the bar & stem attach to the bike.It is often obscured by a plastic plug to prevent water rusting the bolt head.If this doesn't go high enough an adjustable quill stem must be fitted.
If you have the modern design of stem(A-head)you will have to replace the stem with an adjustable type which can be set upto 60 degrees.

I am assuming that you have a standard headset type bike, not an AheadSet style head set, where the stem actually works to hold the fork in place.

In standard headsets, the stem has a jam wedge which pulls tight in the fork stem and locks the stem in place.

Is that wedge missing? Is the bolt that extends through the wedge stripped or worn? You may need a new stem to get it to pull tight.

If this does not help you, post more clearly what is going on.

My guess is that you are using an older, "quill" stem, which is both the STEM (the extension that the handle bars attach to) and the friction bolt that tightens the stem into the STEERING TUBE

Anyway, what I think has happened is that the quill is either not tightened or (because you said you tightened everything) the angled nut at the end of the quill isn't aligned properly and is tightening.

HERE is a great diagram of the quill stem. What I think you'll need to do is:

1 ) IF you have already tightened the bolt at the top of the stem (usually under a little plastic cap, like the one at the top left of the stem in the diagram). Then Untighten it and if you can pull it out make sure that the angled nut (shown at the bottom) is resting properly against the angled shaft of the quill (the vertical part of the stem). As you can see these will spread apart as you tighten the bolt, making them wider and holding them in the steering tube. The idea is to realign the angled nut so it can properly contact the shaft and spread.

2) if you haven't tightened this bolt (maybe because it's hidden), try tightening it a small amount and see if that changes anything.


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This was all written assuming your bike is not using the newer "threadless" setup, which would probably have been fixed if you tightened down the stem (PICTURE OF THREADLESS STEM)