Cool! I was an active member of a couple antique engine and tractor clubs all thru the 90's, until I just didn't have time and space for the hobby anymore. Used to see some real creative homebuilt engines. One guy had scratch built a 2-cylinder engine with 4" diameter flywheels. I think the bores were something like 6" or 7". The thing ran great, and was smooth too.
No, these things serve no practical purpose. But they are a lot of fun if your into mechanical "stuff", and show a lot of ability and talent.

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past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)