Technical Bulletins


For more service bulletins and parts book updates go to :-  

many thanks to Vernon Blair.

These are the interesting pages on major changes which effect compatibility between models in relation to gearbox components and camshaft sprockets and chains. I have also included an interesting paper on battery care and where to look for the matching numbers on the crankcases and the head and rocker box.

This is important if you wish to Use Mikes XS higher ratio fifth gear

17/34 ratio crank and cam sprockets on 256 motors and 18/36 ratio crank and cam sprockets on 447 motors.

Count the teeth on your crank and cam sprockets before you assemble your motor if you get it wrong it will never run.

You must get the correct cam chain to suit your crank/cam ratio too as the pitch is different for each.

Matching numbers

It is also important to make sure your crankcases match as well as your rocker cover and head. Here is where you will need to look to find out is your bits match.

Here on the crankcases behind the clutch

And on some engines at the rear engine mount

Here on the rocker box and head where the oil feed pipe goes up the front of the engine.

Bulletin on new type oil seals

Crankshaft data table for all Yamahas 1980/81