1936 BMW Schneekrad snowmobile.
https://diqn32j8nouaz.cloudfront.net...e_fullsize.jpg
Previously:
https://www.homemadetools.net/forum/...900#post183629
https://www.homemadetools.net/forum/...084#post184290
https://www.homemadetools.net/forum/...854#post171294
https://www.homemadetools.net/forum/...699#post159493
https://www.homemadetools.net/forum/...025#post145080
