Aluminum cylinder heads were a dealer option on 1937–'39 U-Series sidevalve flathead big twin models. They were standard on 1940–'41, 80" engines and optional on 1940–'48, 74" models. These nine-bolt aluminum cylinder heads can be used as replacement for stock aluminum or cast iron heads on all U-Series side-valve big twin flathead engines from 1937–'48. They will also fit 1936 V-Series side-valve big twins with nine-bolt cylinders.
Flathead Power® cylinder heads for UL engines are available in four compression ratios, 5.5:1, 6:1, 6.25:1 and 7:1. Heads are also available machined for either 14mm or 18mm spark plugs. The compression ratios listed are equivalent to the available stock heads in the 1940s. The 126cc combustion chamber of the 5.5:1 heads is equivalent to the standard low compression heads. If higher compression is desired at a later date, heads with 5.5:1 compression may be milled up to .070" which will make them equivalent to stock high compression heads.
Kit contains front and rear cylinder heads and copper head gaskets. Head bolts are not included.
This is a direct replacement for Harley-Davidson® part number 16671-36.
Note: All reference to H-D® part numbers is for identification purposes only. We in no way are implying that any of S&S Cycle's products are original equipment parts or that they are equivalent to the corresponding H-D® part number shown.