A little follow up ...
After speaking with Terry at Northern Photo he said I'd be able to do it if I was mechanically inclined, so I thought I'd give it a try.
First of all it is not possible to remove the shaft on which the wheel rotates. The only way is to disconnect the spring from the carriage.
With the whole head assembly at the top of the column, this is very important, I took the head off the carriage and put it aside, I then removed the column from the baseboard by removing the four bolts on the front of the bracket which holds the column. Now, I'm not talking about the five bolts which attach at the bottom of the baseboard. So, with the four bolts and plate removed you can take the column away from the bracket and lay it on the floor.
At the back of the carriage, I then removed the two screws which hold the spring assembly. While doing this take care because the spring will want to further coil toward the top of the column where the two are attached. So hold the back of the spring assembly firmly holding it to the column shaft. Unscrew the two screws a bit at a time so you can control the spring body.
When neither screw are holding the spring body the whole thing will want to move to the top of the column. Be careful !
You can now slide the whole carriage to the bottom of the column and it will come right off the column. You can now access and replace the rollers as required they just slide off their shafts.
So putting everything back should be the reverse process, you may need a second pair of hands, one pair to hold the spring, the second to put in the screws and tighten up !
I need to wait for the replacement nylon wheel before I can reassemble everything ...
Hope this helps others.
Ron
