Morris Minor Owners Club

The best way is to replace the upright together with the trunnions, but depending how bad the kingpin is worn you can often get away with just the trunnion.
The bottom trunnion carries the weight of the car so you have to be very careful about that thread - the top trunnion takes damper load and even if the male thread is worn, top trunnion failures are very rare (I've never seen one and I've seen a handful of bottom trunnions fail)
Visual inspection of the threads isn't too hard if you know what a good one and bad one look like. It's hard to describe properly but a good thread will still look 'square' and a bad one will look more like a normal screw thread.
If you fit the trunnion and there is still visible slack in the threads then it's time for a new upright. A friendly Minor centre should then discount the cost of the trunnion off the cost of the complete kingpin, as it should be the same trunnion.

im fairly sure i did the top trunion in about an hour....... and its not hard!

Thanks, I have got as far as disconnecting the front wishbone arm, but got a call from work so I'm back online again. All of the play seems to be horizontal, so is it possible that it's just the pin that's worn?

Oh well, I'll find out when I get back outside.

is it possible that it's just the pin that's worn

???
If the threads are worn you can normally 'wobble' it on the thread. Or do you mean it has play on the rubbers? If it is ok on the thread and loose on the rubbers, then just do those not the metal bits.

I managed to get the top trunnion of it's thread in about 15 minutes the other week using Chris' advice to jack the car up on the wishbone? in order to take any weight off the damper arm... if you need to just do the rubbers this would be the easiest way, it's all in a post somewhere...

When I replaced all my front rubbers and eyebolts with poly bushes, I noticed that one of my lower trunnion rubbers was in awful condition so I just replaced the trunnion as it was fine on the threads but the rubber was like mush so I assumed it was a fair age inspite of no wear in the thread and replaced it as a matter of course.
If you are doing the upper trunnion only you dont need to take the lower suspension arm off.