Wrong Again.
It can be too tight,causing stiff steering an "returnability" issues. When you are driving, ball joints are in constant motion as you go over every tiny ripple or bump in the road, as well as steering. Even with grease, this constant movement can cause it to warm up, making it even tighter, causing it to get hotter and hotter, to the point the grease melts out. THEN it can seize up.

the no1. reason why balljoint fails is lack of grease, or running with too old grease that lost it's lubricity. No matter how tight you do your BJ, as long as there is enough grease inside it, parts inside will just slide around and won't get damaged,and will eventually sit in.

negligence

I know the dome nut shouldn't be loose at all. It sounded like people were saying thats the fear if they aren't shimmed/tighted/loved properly. My misunderstanding. 

I will tear into it and see if bad things are happening. Although, I can't get a clear understanding of what "bad things" are. Both upper and lower ball joints moved as they should when finished with the installation. 

To add to what Doug said about the dome nut not backing off:  The original comment about this by Minimans said it might happen "if it is too tight". That would probably be "too tight to the point of seizing". What likely happened/would happen : the joint was far too tight and may have not received adequate grease on the contact surfaces. Under way, the movement caused the joint to heat up and seize. The suspension arm acted like a wrench and forced the dome nut loose... pretty easy to overcome 75ft-lbs and the lock washer with a 1300 lb car pushing on an 8" to 10" lever. What would that be - up to 800 to 1000 ft-lbs? The lock washer would peel away well below that, maybe around 200 ft-lbs. (Don't worry Tony... proper greasing prevents that!)

Hit all zirk joints if no grease comes out from under rubber there will be a problem. Steve (CTR)

???

The dome nut should never be loose or backing off when properly fitted.

AFTER lapping and cleaning, tighten the dome nuts to full torque with the shims fitted and lower joint spring OMITTED.  Then check the pin stiffness as Dan described.  The fit will almost certainly be "wrong" requiring changing the number of shims.  Repeat the process over and over again until you get the proper pre-load on the pins.  THEN disassemble one last time to fit the spring and apply a bit of grease.  Torque the final assembly and make a final check on the pin pre-load.  When it all checks out, use the zirk fittings to apply more grease to the joint.

Refitting the same number of old shims when fitting new parts is not going to be correct at all unless a miracle happens.  
If you didn't do all the steps as Dan and Malcolm said, you owe it to yourself and your safety to do the job again.

Thanks for the advice. 

Both ball joints were installed with the number of shims that were there to begin with (3). The top was stiff without grease...the bottom even stiffer (difficult to move). Thats what I meant by looseness (the ability to move the stem around) The grease helped. They are not pulling in or out as if they are bad. When I say I checked them, I took the wheel off and checked to ensure the dome nut had not backed off and pushed the lock washer at all. I am hearing that I should check to ensure that the dome nut is backing off even with the lock washer.

easteregg: how did you "check" them after a couple of weeks? What do you mean by "looseness"

When properly assembled dry - no grease and no spring in the bottom joint - the stems, before you connect the upper and lower arms, should be just movable under hand/finger pressure. Being stiff, there should be no "looseness" at all. Adding the springs into the bottom joints makes them very stiff to move. Adding grease makes it easier to flex the joints.

On some vehicles ball joints used to be checked by jacking up the car to wiggle the hub. Depending on the vehicle a jack had to be inserted under the suspension in an appropriate place to "unload" a ball joint. You can do that to some degree with a Mini - if you could jack under the upper arm to take suspension spring pressure off the upper joint. But it wouldn't work with the lower one because of the small but strong spring inside the ball joint. You could separate (one at a time) the upper and lower arms from the ball joints and flex them with your fingers. Top should be stiff, bottom stiffer. any less is not very "good".

Only careful inspection will tell you if you are "good".

Not to alarm Tony, but a ball joint is most likely to fail because it is so badly worn the stem pulls out of the dome, or the stem snaps from massive over-stress or a flaw. I actually had one go once on me on a FIAT x/1-9. The day after a 5-hour highway drive, I was turning a corner at very low speed and a front wheel slipped sideways off a ridge in the pavement (an ancient streetcar rail protruding through the asphalt). The ball joint (bottom, because of a McPherson strut suspension) just.... snapped. The front of the car was so light I could lift it and prop it up on the strut and then roll the wheel (and the car) over to the curb. No damage! Just a flawed ball joint.

Did you shim them ? Did you check the tightness with the springs removed ? Did you lap them in first ?
If you missed even one of the above you need to re do them correctly, if you missed all three i wouldn't drive it.

Not to sound like a 4 year old, but...when I torqued them down (them being the ball joints) there was enough "loosness" to move on the top, and less "looseness" at the bottom. After a couple weeks I checked the ball joint and it didn't back out or anything...am I good?

What are some other symptoms?

Wow ,i had no idea there was that much to it lol

I thought it was simple as torque it down and go! Lol im glad i asked .

Cars getting faster and any sort of play reduced makes the power much more manageable .Its cool how much a little bit of power makes a difference when a car is soo light.Every PSi of boost you notice a decent gain.I had a turbo civic beside me last night ...same motor and more boost then me and i pulled right away.

If you are worried about a ball joint snapping, you should never get into a vehicle of any kind again. Just about all modern cars have ball joints. Even your Toyota truck.
Ignore the naughty side of your brain... it has no idea what it is thinking.

that's what i'm worried about sir Paul, if the balljoint snaps, that will be it!.. i believe you have to tighten it, for as long as you can move the tee, it's ok...if you tighten it too much,that's wrong, you can just imagine how much tons of pressure the car applies to the balljoint everytime you hit a bump, with only those fine thread holding it to the hub. it's scary. and now,sir paul said , even with a lock tab in place, the nut can still loosen, that's even scary-er. i guess the Best thing to do is too tighten it to the proper specification based on haynes manual, and slap some shims as needed.

(the naughty side of my brain is telling me to put a hole and a cotter pin on the balljoint/ but there's no way because the grease will spew out from the hole/ i'll drop this proposal) But im really surprised, the lock tab can be overcome'd after all.

Get back in there and recheck the pre-load!! if they are too tight the ball joint will loosen the nut even with the lock tab and the result may be dissastrous.

You need to get the pre-load on the ball joint correct. To do so, you need to assemble it with the retention washer and an assortment of shims and torque it to spec. If the joint is too tight or to loose, you need to disassemble and re-shim, then re-torque.... until it IS right.
Note also, you may need to remove all shims and take a bit of material off the dome nut - the emery paper on glass trick - to get the pre-load right. Lastly, the ball joints with the springs are pre-loaded without the springs, which are inserted after you get it right.

I just replaced all 4 on mine. Not too bad a job. 

What is meant by having to retighten the dome nut? I just cranked it down, bent the retention washer and drove it. Did I do a bad thing?

 

There are two possible ball joint types, all minis should have the rebuildable type. Metros use a replaceable ball joint that is not rebuildable. People use the metro hubs on minis but require the correct ball joints and adjustable lower arms to correct alignment. I bought the deep 1 1/2 Snap on socket for ball joints for minis. The Metro ball joints ate metric. There are currently several different type ball joint kits out there. Quality differs so try and buy the best you can find. Some of us over the years have lapped the ball pins to the nut. Be careful to use only fine or extra fine valve lapping compound. Just till they are uniformly gray where they contact. You will notice a small flat in the face og the ball they are there to allow grease to escape. Lapping sometimes removes the flats. If that happens make new tiny flats at least two 180 degrees apart. Failure to release grease will keep joint from accepting grease and joint will gauld. Save your old shims new kits rarely supply enough. If you over lap and have problems fitting you can reduce the height of nut by sanding on glass plate with emery glued to it. I have a steel bar 1/2 x 3 x 12 machined a radius in one side and drilled two holes that line up with disc mounting ears. Chuck in vise and go to work. Steve (CTR)  

I am sure you will get lots of advice.  I encourage you to also search for old threads as ball joints get a lot of discussion.

To the best of my knowledge, there is only the one size of Mini ball joints.  Don't confuse those with Metro parts.

The bottom joints may seem like they have less play in them.  However, if I am remembering correctly, it is the bottom joint that has the compression spring under the contact pad.  That will make the bottom joints feel tighter than the top when both are worn.  Don't assume the bottom ones are "good".

There are a lot of discussions about the quality of new replacement parts vs NOS replacement parts.  That is information that warrants digging up old threads.

My only bits of advice on doing this job are as follows.

1. Make some form of fixture to allow you to hold the hub in a vise so you can properly torque the dome nuts.  
2. SAVE any of the old shims you remove from the old joints.  Expect to use some of them.
3. Hand lap the new ball joint parts so they fit properly (again... old threads).
4. Finally, the manuals and online videos will show the shims located between the dome nut and the keeper plate that prevents the dome nut from loosening.  I assemble this differently.  I place the shims between the hub and the bottom surface of the keeper plate.  That prevents the dome nut from ruining the shims.  
5. Anticipate tightening the dome nut several times to check the pre-load on the pins... then loosening them again.  Don't expect to get this right on the first adjustment and don't expect a good fit of the new parts without lapping.

Did all new wheel bearings on the front of the mini today,its an 88.Glad the car had this stuff with it and it really needed then.I noticed the bottom ball joints seem decent and tight but both uppers are worn and need replacing.Im going to probably just replace all 4 at once but it seems they screw in and are taken off with a large wrench or socket...

Is there more then one style for this? Id hate to order them and not fit and have the car apart for a little waiting on parts.Anything to look for or just one fits all?

Im trying to tighten up the front end as much as possible.The wheel bearings really helped a lot and made it way quieter.I thought a lot of it was tire noise but i hit a turn going pretty fast and it got quiet and i knew that something wasnt right.