My mongoose mountain bike's hexagonal shaped nut won't tighten on the bike stem?

Yes, all bikes have handlebar height adjustment.

How to Adjust the Handle Bars on a Mongoose Mountain ...

DIY Mountain Bike https://www.diymountainbike.com > adjust-handle-bar...
This is done by loosening the bolt and clamp on the front of the stem. Insert a 6mm Allen wrench into the bolt head and turn until the handle bars roll freely.

How to Raise Handlebars on Mongoose Mountain Bike

mtbrules.com https://mtbrules.com > how-to-raise-handlebars-on-mo...
Oct 2, 2022 - You can adjust the handlebars from front to back by loosening the clamp bolt in the stem's front. Insert a 6 mm Allen wrench into the bolt head.

How to Raise the Handlebars on a Mongoose

SportsRec https://www.sportsrec.com > Fitness > Strength Training
Jun 29, 2011 - Other options for raising Mongoose handlebars are adding a new riser bar, which can give 1 to 5 inches of height for your handlebars. A steer- ...

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Product Manuals

Mongoose https://www.mongoose.com > pages > product-manuals
The Mongoose owner's manual contains important safety, performance and maintenance information. Read the manual before taking your first ride on your new ...

Mongoose full-suspension mountain bikes, like the Ledge 3.1, have a little bit of height adjustment for the handle bars. See the manual at https://www.mongoose.com/pages/product-manuals . The current link to the appropriate manual is https://p.widencdn.net/brqquy/OMMGFS-1_Mongoose_FullSuspension_OM . Start at page 18 (20 of the manual in the browser) and determine the type of stem on your version of the bike. The quill stem version has minimum insertion marks that must be below the top of the headset and not visible. For the threadless stem version of the mountain bike, you adjust where the handlebars clamp onto the steerer tube. However, this is very imited since there should be only 1/8" to 3/16" gap between the top of the handlebar stem and the steerer (stem) tube. The is where the top cap and bolt to replaced on the handlebar stem and thread into the steerer tube.

I hope this helps.

Cindy Wells

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Thanks.

There are typically two allen bolts that mount on the side of the handlebar stem. Those should be tightened. The top one should only be tightened to remove up and down play in the headset. If you tighten the top one too tight, steering will feel clunky. Only tighten the top one tight enough to remove the up/down play. Use the side bolts to keep the handlebars from turning relative to the wheel.

there is a spring tesioner but probally need to take a link or two out of chain

You haven't given me much to go on, but a common problem is to mis-identify where to tighten. There is a large nut (about 1-1/4 inch) that is the locking nut for the headset (which is where the bearings are that allow the fork to turn and steer the bike). This large nut does not tighten the handlebars. Rather, there is a long bolt that travels straight down through the handlebar stem. The handlebar stem is the bar that clamps to the middle of the handlebars and extends vertically down into the headset. At the bottom of the bolt (where you cannot see it) there is a wedge shaped nut. When you tighten this bolt the wedge nut jams itself inside the tube which is the top of the forks inside the headset, thereby locking the handlebar stem to the the forks. The head of the bolt you need to tighten can have a variety of shapes - could be an ordinary hex head, or it may require an Allen wrench (hex key). There are lots of different styles, but if you Google images of "handlebar stem" you will get the idea. good luck. Al K

You need an Allen wrench (a.k.a. hex key) to fit the bolt head right in the middle of the handle bars. Loosen this bolt just 2 or 3 turns then tap the head with a soft hammer or block of wood and a hammer. Then pull the handle bar stem up (and all of the way out so you can see how the wedge-shaped nut at the bottom of the stem works). Look for a mark on the stem telling you how high you can safely raise the bars (you have to leave enough of the stem inside the tube so that it will be strong.) Put it back in and tighten it up. If you found this helpful, please vote. Good luck

The crank has to be removed to tighten the nut that holds the gear on. I assume that is your problem is with the chain gear on the sproket that is loose

where the bars slide into forks there should be a allen nut on the top undo this slightly and adjust bar height then tighten up allen nut

There are usually plastic caps hiding a 14mm nut or bolt on the arms. Unsrew or snap out the caps and tighte n the bolts w/a socket wrench