as previously mentioned my '72 six day is motor is froze up from rain dripping down the throttle cable into the carb then the lower end(the piston was at tdc) there is a 6b motor on ebay, mine is a 6a, what is the difference? are they interchangable? i'm not a numbers matching kinda guy,,, i just want to ride my penton. is there a number breakdown somewhere? i have seen a 5a motor also. i'm guessing "125"cc "1"cyl "6"spd "a"version ?
Any of the 1251 Sachs engines with aluminum cylinder will work for you, but the B engine is a more current version than the A engine.
Donny Smith
I can add a little to what Donny said. The A engine has larger diameter crank wheels than the B engine. Normally in stock form a B engine will rev faster and make more HP while an A will have a broader powerband and more low end. If you use the search feature at the top of the page you can find a lot more discussion of the differences.
Dennis Jones