Re: 1936 aluminum heads dome/no dome
frnkeore...The "40" prefix head came out in 1933 as an aluminum head with 18mm spark plug threads. In 1934, "A" was added to the part number as a suffix to distinguish the aluminum head from the cast iron "B" head. In July 1935 a new designed "A-2" head was introduced necessitating that the original "A" head suffix be changed to "A1". Both "A-1" and "A-2" heads were used thru the end of 1936 production.
Here are some photos showing differences between the "A-1" and "A-2" heads as well as the domed "48" head.
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