Transmission

 

1. Better Gear Ratio in the upper 3 Gears

 

For the performance characteristics of a race engine, the gear ratios of engine types 351/352 in the upper three gears are not close enough together. Since engine type 521/522 the upper 3 gears are in closer steps. Gear shafts of 351, 352, 521, 522 are interchangeable.


Transmission gradiation

gear 351/352 521/522/1A2/31k/1WW
1  2,57 2,57
2 1,78 1,78
3 1,32 1,32
4 1,04 1,08
5 0,89 0,96
6 0,79 0,89

1.2 The primary transmission ratio of the RD 350 and the RD 250 aircooled are different

Primary transmission gradiation  RD250: 21:68
Primary transmission gradiation  RD350: 23:66

 

Oil pump transmission RD250         21:22
Oil pump transmission RD350/400: 23:21

 

 

To convert a RD 250 engine to the primary transmission ratio of a RD 350 the following parts needs to be changed:

  • Plastic wheel oil pump (21 teeth RD350 - Part Number 278-13178-00 RD250 22 teeth )
  • Plastic wheel tachometer drive (20 teeth RD350 - Part Number 278-17851-00, (RD250, 18 teeth )
  • For 350cc cylinder you need longer studs Part Number 248-11361-00 or tinker as described here