Terrier Forks (T15 model)
Tiger Cub Forks
The first Tiger Cub T20 models (1954-1956) carried on using the grease-filled forks fitted to the Terrier, but for the 1957 model year a new hydraulically damped front fork assembly was fitted.
Be aware: the early grease-filled stanchions are not interchangeable with the hydraulic fork ones. The early stanchions are 0.010 inch larger in diameter.
Basically three types of hydraulic front forks were fitted to the Tiger Cub depending on the model - lightweight, lightweight (Bantam Cub) and heavyweight (from the 350/500 twin-cylinder Triumph models but with shorter stanchions and lighter springs).
The T20C (1957-59), T20CA (1958-59) used lightweight forks fitted with 1 inch longer stanchions tapered to fit into reinforced yokes.
From 1965, selected off-road orientated models were fitted with heavyweight forks which had the springs outside of the stanchions.
Note: the heavyweight forks fitted with external springs take an extra 50cc of oil each leg - 200cc rather than the 150cc of the internally sprung type.
Lightweight forks (Cub and Bantam) - 75cc per leg.
Oil change notes
by Roy Shilling
To change the fork oil on lightweight forks the drain plug is also the 'boomerang' mudguard stay bolt/stud into the bottom side of the slider. Take the nut off the outside and remove the stay, then remove the stud to drain the oil out. Discard the fibre washer.
Undo the top nut, (on T20 Nacelle equipped bikes, there is a filler hole in the stanchion behind the headlight) one side at a time if you don't want to take the wheel out and gently work the suspension up and down to push out the oil. I say gently because if you don't, any oil in there will be forced out like a jet......
Once all the oil is expelled, put the drain stud back in temporarily and put some brake cleaning solvent into the stanchion from the top. Re fit the top nut and work the suspension up and down a few times to 'swill' the fork leg and dislodge and crud, and there will be some!
Remove the drain stud and allow to drain taking the top nut off and working up and down gently to expel all the contents.
Once complete and the solvent has evaporated, refit the drain stud and a new fibre washer - Do not over tighten.
Put in 75cc (1/8 pint) of SAE30 oil and refit the top nut, boomerang stay and that's the first side done. Repeat for second leg.