See also in the REF section of the Sportsterpedia:

• Breather Valves (1957-Up) (list of breather valve changes)
• Breather Venting / Relocation
• Evo Crankcase Ventilation (1986-Up)
  

L1984-1990 umbrella valve (26856-82).
1991-2003 umbrella valve (26856-89).

Dims: ¹⁾
Outside diameter:
L1984 - 1.25“
1991 - 1.0”
Edge thickness (1/8“ in average):
L1984 - 0.036”
1991 - 0.041“

• The pic below shows the left side (filter side) that faces into the cam box.
  • It's center inside diameter is slightly larger than the 1.25” OD (-82) umbrella valve.
  • The two 'C' shaped slots that do the breathing have an OD of 1“.
  • As a result, the 91-03 umbrella valve with its diameter of 1” may not perform correctly in L84-90 models since there is likely to be leakage.

Umbrella (check) Valves L - (26856-82), R - (26856-89) 2)	Breather Baffle Tube (26917-84) 3)