The workshop factory manual and or service bulletins cover this topic quite well and well illustrated and clear instructions.
(early models use a collection of service sheets for both twins and singles, later models are covered in a factory manual. Much of the fork parts are similar or the same in a Unit type twin such as A65).
This all assumes the parts come apart easily, and near 50-70 years on they can be challenging to take apart. The fork seal holder, shroud assy on a BSA can be really challenging. Much use of expletives, heat, penetrating oils and leverage. Sometimes several days of heat and oil can be the case. The special tool for the shroud/oil seal holder is a MUST have and a good quality one is critical. You can make your own, but the small tabs have to well done and heat treated.
Torch and oil to heat treat them. It is not unheard of to destroy the shroud/oil seal holder on a old set of forks and thus replacement required. (Been there-done that) In building up project bikes or restorations I have had some terminal cases where it took several fork assys to make one good one. I have one now for my 52 BSA B33-Goldstar bitsa that I suspect is too rusty to save much. (much penetrating oil and expletives will be applied this week)
Early BSA forks tended to be not plated chrome (its a hard industrial type chrome, not to be confused with decorative chrome) and often were plain steel. some people paint them or chem treat them to prevent corrosion but at the sealing surface they have to be smooth and clean to function (no layers of paint). later style can have the surface treatment wear thru and some will still run them, others replace.
But the forks, once in the triple trees can become quite locked into place. Again, each model differs but many have a pinch bolt and I use some steel wedges into the slot to open that opening up to free the leg, but on a tapered top tree or no pinch arrangement you have to break it free. (Heat-oil-leverage) metal strap wrenches, Plumbers pipe wrenches and channel locks carefully used are the next step.
Here is some pix of the tools that you need or will need to order. 2 styles of fork draw tools (mostly installs) and the seal holder tool. I actually have several styles of these for different models (Triumph for example) This one is a spitfire brand and seems well regarded. I either bought it off FeeBay or Walridge motors in Canada. Walridge has an excellent selection of tools and I often refer people to them. Nice people too. Many other vendors carry this stuff. You COULD make these tools as well..
Oil seals: Haha! thats funny! (have you heard the penguin joke about this?) So, Oil seals and British bikes is kind of an oxymoron in many ways. later model bikes have traditional oil seals with a rubber or viton type construction tensioned with spring type material. Time change items that require replacement sooner or later. Early types such as pre 1959 Triumphs dont use a seal per se... its a piece of cloth felt material, and in some cases on some vintage machines its leather! I use to keep a sample fork oil seal holder on the work bench for a mid fiftys triumph as well as thumb tabs on some parts book to illustrate this. On the Triumph forks I suggested that you have better luck at oil retention by using a ladies sanitary napkin or Kotex tampon.
Some of my shop customers needed a great deal of education about what IS and what is NOT possible regarding their machines.. Early primarys for example.
If you dont have factory literature, it can be downloaded off the internet on multiple websites Some material is more challenging to locate than others, but most is availible for free downloads. If you like, PM me with your exact year and model and perhaps I have it already in digital format and can email the files. You can then take to any printer and make copies. I recomend placing the copies in plastic page protectors and a 3 ring binder. Shop materials tend to get soiled easily.
Last picture is my grotty forks for my Goldie bitsa, pray for me!
