14 Page – PDF Download – Complete Series – Yamaha RD400 Engine Stripdown

“Yamaha ‘RD’ Twins

The 400cc version of the immensely popular air-cooled Yamaha two strokes seems to have survived the 1970s breakers’ yards more successfully than its 350 and 250 predecessors. This engine strip by Chris Dell can be used to work on all three models.

The engine looked at here is a 1976 RD400. As far as stripdown procedure is concerned, many of the RD engines are much the same.

Effectively this strip applies (with a few minor differences) to A and B models of RD250 and 350, C and D models of RD250 and 400 as well as the YR5 and YDS7.

The later RD250 and 400 (the E and F) are much the same except for having electronic ignition and a different generator. The design shown here has the rotor inside the stator, which allows the crank to be removed without removing the rotor. The E and F have the rotor outside the stator and on these, it is necessary to remove the rotor before the engine can be stripped.

The liquid-cooled RD250LC and RD350LC share their basic layout with the earlier air-cooled models. They use the same type of generator as the E and F, with electronic ignition, but obviously there are changes (including a water pump) to suit the use of water cooling.

Pre-RD models (the YR5 and YDS7) are much the same as the 400 shown here apart from lacking reed valves and the 400’s extra sixth gear. There are various other minor differences between different years and models, the clutch, for example.

These are all easy motors to work on. There are no peculiar design features at all. This is just as well as the 400, in particular, is not very reliable. Problems include crank failure and gearbox trouble – as well as a predilection for rebores at depressingly short intervals…”

14 Page – PDF Download – Complete Series – Yamaha RD400 Engine Stripdown

engine stripdown

Yamaha RD400 Engine Stripdown – PDF Download