Oh dear, I just did 2 hours of typing and when I went to post the info, I lost it all from the breakdown of the site. Oh well, thems the breaks. I simply must copy all the info before I post it. Here is about 25% of it that I have retyped. (My wife is so thankful for my patience)

When I worked as an Instructor in a machine shop in the USA, it was my job to install and service a new Surface Grinder. This is a high precision machine that produces a near perfect flat surface. Before the grinder can be used, the grinding wheel must be perfectly (!) balanced. This was done by mounting the wheel on a special mandrel (a precision bar) and placing across two knife-edges. These knife-edges were leveled with a precision spirit level built into the base of the knife-edge frame. The wheel with the mandrel was placed in-between the edges and alowed to rotate. This enabled the wheel to be perfectly balanced and ready for use. These wheels were only 175mm dia x 15mm thick.
To balance your L/Y wheels, try this.
Get two lengths of 20mm dia. cold rolled bar about 800mm long. Check the required length to suit your wheels. Place these bars on the kitchen table spaced about 125mm apart. they must overhang the table edge by at least 3/4's of the dia. of your wheels. Clamp the ends down on the table with whatever your wife will alow. Now level the table with a good (?) spirit level. Check the level of the overhanging bars as well and especialy across the bars. Ajust the table legs with suitable packing until the bars are as level as you can get. It will help enormously if you polish the bars with a fine grade of "wet & dry" paper. Now get another suitable bar that fits perfectly thru the wheel bearings. It should be about 100mm longer than the width of the wheel and long enough to sit across the two bars clamped to the table with at least 25mm overhang. This bar should also be polished the same as the other two bars but only polish the ends that will sit over the two bars. The polishing cuts out all the friction in the set up. Slip the bar thru the wheel bearings and place across the two bars on the overhang from the table. The wheel will revolve and respond to the most minute imbalance. Cut some lead strips or flatten a fishing sinker and tape them onto the top of the wheel, ajusting the weight as needed. When the wheel is balanced, fasten the weights permanently. You might want to cut the weight in half and fasten each piece to each side of the wheel. This is to keep the wheels dynamicly balanced, ie, so that one side is not heavier than the other. How you fasten them is your problem but they must be secured so they wont fly off. This technique works and is very sensitive because of the infinitely small contact area between the bars. The wheel is perfectly balanced when it will stay in any position without starting to revolve. I think you will be amazed at just how accurate and sensitve this is. Let me know (let us all know) how you get on using this technique.

Kody

Well this worked very well. I used Kody's method and balaced the wheels with normal car wheel weights that my local garage gave me. The worst wheel needed almost 40g to balance it and the best needed 15g. Now I just need some wind to test them