Rotax egines

[Slakewell]

Did Rotax make an open class engine before 75?

[Brian Watson]

In a snowmobile maybe..

[djr]

Could be wrong, but I think they only had the 175 + 250 disc valve engines in 1975

[supermoto.mc]

No but you could fit the long stroke Conrod maybe and go to 280 your bore should be 74 !

[pokey]

It reads kind of obscure but FWIW

Canned ham

In 1974, an attempt is made to enter the 500cc Motocross class. The Type 406 is introduced via the intermediate step of the Type 366 in 1978, with an output of approximately 48 HP at 6,700 rpm.

I read that as they started with a probable prototype(maybe type 366) in 74 but didnt get there till 78 with the type 406

https://www.rotax.com/en/100-years/history-of-motor-sport.html

[sleepy]

No but you could fit the long stroke Conrod maybe and go to 280 your bore should be 74 !

Length of conrod doesn't change the stroke only pushes the piston further up the bore. Would be possible to weld and re-machine bigend hole further out to increase stroke and make and fit a larger sleeve/piston to get one into open class but gets expensive.

[pokey]

Ummmm yes longer rod doesnt change cc but it does change the speed of the piston;)

[Slakewell]

Thanks for the info guys so the short answer is NO