I thought you might be interested to see the crank & internal parts of the magnesium Yamaha YX24 / RR250 engine.

The engine is (unbelievably) like new inside. It does not look as is if it has ever been taken apart before.  In fact it was probably the easiest to strip down "early" Yamaha engine I've ever done. All the screws came straight out and the crankcases pulled apart very easily.

For those of you who are familiar with the Yamaha YDS series you will agree that Richard's early 1960's engine internals are really brand new.

As you can see the crank is in very good condition, but take a look at the conrods!

They have been knife edged ground and polished - although they are still the (CM21 stamped) YDS1 rods with the bronze bushed small ends. This must have been done from new as there are no marks that show the crank has been apart, and there is no way they could have been ground once installed onto the crank (without damaging the crank wheels).

The bare crankcases are at least 1/2 the weight of standard alloy ones, if not lighter.

Anyhow the cases are now going off for glass bead blasting and chromate coating.

The gearbox is the late type YDS1 with YDS2 ratio's, primary reduction is still YDS1.

So far we had no reactions about this engine, hopefully someone knows more!