I can't figure out how to adjust the stem on my 77 nishiki,

I loosed off the Allen bolt on the top of the stem, and loosened off the large nut near the head tube but I can't get it to go up or down..

Sorry for the cell phone quality picture

Well that large nut has nothing to do with loosening the stem, your headset will now need to be adjusted, you need to knock the allen bolt on the top down with a hammer, whack the allen wrench not the bolt itself or you can deform the bolt, if that doesn't work your stem is most likely seized, there are many threads on removal of seized stems

invest in a rubber or plastic mallet, old bikes like that need hammering sometimes and that's the tool for it. Hammering on an L shaped allen wrench can sometimes be tricky and may lead to deforming your quill bolt.

The large nut at the top of the head tube, is the locknut for steering bearing adjustment, which is adjusted by the knurled one underneath. If you havent turned that, rethighten the locknut. If the stem is seized, try dribbling ammonia down to unstick the al stem from the steel head tube.

actually before you 'tap' on the stem bolt with the handle of the hammer make sure it is still engaged in the threads of the 'wedge' so that does not drop down the steerer tube.

However more importantly here is the fact there is a "MAX HEIGHT" limit marked on your stem. besure you do not raise the stem above this mark. you might be there already. raising the stem above this limit could result in injury or damage to the bike

Bianchigirll is right. Your Nishiki uses the odd 21.1mm stem diameter. I've seen several bikes with these stems and all were relatively short. I suspect you are at the max height right now. There are many threads on these stems and what to do about them. As one who has been through this with a 1981 Schwinn Voyaguer I can tell you that your options are:

1) Live with your current stem
2) Scour eBay for a 21.1 (typcially marked .833) stem that is long. I've seen them on eBay, but rarely.
3) Buy a new 21.1 extra long stem. They are on eBay and online retailers. They are low quality, heavy, steel and hideous looking but they work. Attached is a photo of my bike with this option.
4) Find the stem you would use in a perfect world (I used a Nitto Technomic). Next, find a small machine shop and ask the proprietor very nicely to put your new stem on the lathe and turn it down to 21.1mm. Be sure that you and the machinist are in agreement as to how high up the stem he will reduce the diameter. There are some people who will tell you that reducing the stem's diameter this way is unsafe. These people know nothing of what they speak. Do not listen to them. If you need evidence look no further than your original stem. It is a 22.2mm diameter stem that has had a portion reduced to 21.1 on a machine. I asked Yellow Jersey to do this for me and they refused on safety grounds. I don't blame them for not wanting to be liable, but that doesn't change the fact that their concerns are unfounded. See photo of my bike with this option.

As for removing your stuck stem, try the following. Remove the front wheel. Hold a 1"x1"x18" piece of wood or similar length of 2x4, or axe handle (or. . you get the point) between the fork blades at the crown. Use this as leverage and twist the stem by grabbing it around the handlbar/clamp. Be careful and use caution. This should release the stem. If not, then it's REALLY stuck and you'll need to do a search for the myriad threads on this topic.

google got me this:
https://www.google.com/search?sourcei...1.1+bike+stems

thanks for the replies, with some penetrating oil and a bit of muscle I freed the stem (and re-tightened the lock nut for the steering bearing).

The stem was almost at its maximum height but fortunately I needed to lower it rather than raise it. I took it for a 50km ride yesterday evening and I was pleasantly surprised by the fact that all the bolts had been tightened sufficiently and neither of my wheels fell off. Thanks for everyones help.

Lightly grease the stem itelf and the threads for the wedge before you re-install it. You will avoid the problem in the future. Loosen it, move it, reposition and tighten every year to avoid siezing in the future (it takes 1 minute).

this is a very old thread but I'm running into the same problem, I did the same thing on my Univega Gran Rally, I thought that to adjust the stem you had loosen the headset nut and then loosing the allen bolt on the top of the stem(?).

If I loosened the large nut on the headset and tightened it back up do I need to get it readjusted?

NB: there is a height limit mark on the stem, do not raise it above that mark.

head set top nut has nothing to do with stem height ,
it is the lock nut that keeps the headset from going out of adjustment.

If you messed with it, you need 2 wrenches , one of them a specifically
made headset wrench to do it up right, again.