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Cylinder Head Porting, Antique and Hi-Performance American Motorcycles


Back "in the day" automotive valves were typically shortened for use as oversize Knuckle intakes. While period correct, they have a few drawbacks. Shortening the valves require the use of a lash cap on the valve tip to prevent premature wear, which can throw off rocker geometry. Often automotive valves have a lot of "tulip" which requires the bottom of the already short Knuck guide to be further shortened. They also tend to be very heavy, which does nothing for performance. These 5/16 stem valves address all of those problems.

A Lee's Speed Shop Exclusive!

 Knucklehead intake valves with a 2.060” head diameter and with .310" stem diameter to go along with our 5/16" bore Knuckle valve guides. Head diameter is 2.060" (approximately 5/16" larger than the stock  1-3/4") w/ 23 degree tulip. These valves may be used as a performance upgrade for all knuckles 1936 to 1947 when converted to 5/16 bore guides.  This is the largest valve size that can normally be used with stock (74") bore Knuckles.

Overall length on these valves is 3.675 which is .110" longer than stock. The extra length means you will not have to "sink" the valves so deep to maintain proper valve stem protrusion. As with any oversize valve, you should check valve to valve and valve to piston clearances.

These valves are manufactured by Kibblewhite Precision Machining exclusively for Lee's Speed Shop, to our specifications

Lee’s Speed Shop 2.060 Knuckle intakes are the proper diameter to "do it old school" by removing the existing seat insert and grinding the new seat directly on the head. By blending the material from the bowl into the I.D. where the old valve seat was, you will wind up with a "choke" of 90% which is just about right for good flow on a Knuckle head. Oversize valve seats could also be installed if preferred, and may be necessary if using these valves with S&S Knucklehead castings.

LSS Knuck valve 009

All Lee’s Speed Shop parts can be purchased securely online by following this link to our eBay store.

Lee’s Speed Shop on eBay