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Cylinders for 1941–'47 OHV Big Twins

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These cylinders for knuckles and KN-Series engines are made of the same engineering-grade grey cast iron that we have used for years in our cylinders for shovel engines. As a result, these cylinders have very high tensile strength and excellent wear resistance. Cylinders are available unfinished and with a durable black powdercoat finish. Available in 3 7/16" and 3 5/8" bore. Different length cylinders are also available. Fits 1941–'47, 74" knuckle engines and Flathead Power KN-Series engines.


  • 3 7/16" or 3 5/8" bore size
  • Available in sets or single front or rear cylinders
  • Available fit with your choice of S&S pistons

These cylinders are now "configured to order," which allows customers to order a set of cylinders only, a front or rear cylinder, or a set of cylinders fit with a set of S&S pistons of their choice. In addition, S&S offers machine shop services through the S&S remanufacturing program. New pistons can be fit to your existing cylinders for a reasonable charge.




Typical Cylinder Dimensions for 1936–’47 OHV Engines  & Flathead Power® KN-Series Engines 
Model Year   Displacement   Cylinder Bore   Cylinder Length   Notes 
1941-’47   74"   3 7⁄16"   5.530"   No Fire Ring  
KN-Series   93"   3 5⁄8"   5.625"   No Fire Ring  
Special     3 7⁄16" or
3 5⁄8"
Specify   You Tell Us!  
*Cylinders for 61" knuckle engines are not available from Flathead Power®. Cylinders for stock 74" knuckle engines and Flathead Power KN-Series engines do not have a fire ring  on the head end of the cylinder.  


NOTES: Flathead Power cylinder heads for 1940–'47 OHV big twins are machined for 7/16-20 head bolts and are not compatible with stock 7/16-16 head bolts. If using FHP heads with 3 7/16" bore cylinders, stock style hex head bolts for 1948–'65 big twins, part #106-4523 may be used. Flathead Power 3 5/8" bore cylinders require the use of FHP 1966–'84 style 12 point head bolts part #93-3024, due to clearance issues.
Stock 1930–'78 hex style base nut kit is available in cadmium plate, part #106-4522, for 3 7/16" bore cylinders only. Stainless raised hex base nuts, part #93-3063-S, are required for 3 5/8" bore cylinders.

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