Yamaha RD1200 V6
He’s back on with this amazing project – probably the ultimate two-stroke build seen in the UK.
Iam building what I hope will be the ultimate two-stroke, a 1200cc V6, based on one and a half RD500 engines using Yamaha Banshee race barrels and heads. A good customer of mine, Ian Buxton has commissioned me to build it and he intends to have a bike built based on CMM’S Retro Reboot Yamaha RD500. In January 2015’s CMM (issue 327) I covered the initial cutting and welding the crankcases and in the following issue I covered machining and welding the barrels to suit the different stud spacing of the Banshee barrels and the RD500 cases. This month’s missive continues with the project, so let’s get on, shall we? One thing that I have to think of when building this engine is that it must still be rideable on the road: i.e. the Banshee barrels don’t have powervalves. With this in mind I am using 8mm longer con rods on the cranks – this will give more torque. The stroke of the RD500 is 50mm but the stroke of the Banshee is 54mm so the cranks were modified to 54mm to get the port-timing right and also the longer stroke will give more torque. To achieve the longer stroke was tricky: the crank-pins that the big-ends run on are part of the flywheel webs on the RD500 cranks. If the crank-pins were bored out to fit offset pins the holes from boring them out would be too close to the hole through the centre of the flywheels. The crank-pins had to be ground off and the flywheels bored 2mm further out to take the new pins (it is 2mm, because to get a 4mm longer stroke, the piston will have to travel 2mm further up and 2mm further down).