RD1200 V6 part 4
The ultimate two-stroke He’s not been idle has our Stan, but building the best, by the best, takes time.
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his is the latest instalment of the designing and making of what I hope will be the ultimate two-stroke engine, it’s a 1200cc V6. Those of you with long memories will recall that the project started when I built a 750cc version of the RD500LC engine using 350 YPVS barrels and long stroke cranks. I wrote about the building of the engine in CMM and when I finished the project and wrote the final article on the RD750 V4, at the end of the article I put “now for the 1200cc V6”. It was meant as a little joke but a customer, Ian Buxton, persuaded me to build one for him. With the lovely Retro Reboot on the RD shown in CMM in January 2014, I think he now wants to go with that as a home for the bike, too. The shot here is the lesser-seen Kenny Roberts replica, but if you want to check out the work done so far, then the previous CMM articles on the project have been issue 327, issue 328 and issue 333. With the crankcases welded and machined and the cranks built, the barrel 86 / classic motorcycle mechanics
spacer plates made and the barrels welded and modified, it was time to do a dry build to make sure it had all turned out as I had expected/hoped. Thankfully, there were no unexpected problems. Up to this point everything was planned and were variations of what I had learned with the RD750LC engine build. The next part of the project was the inlet manifolds. On the standard RD500LC the inlet rubbers have a right-angled bend in them so that the carbs come out two
Here we have the crankcase inlets blanked off.
on each side. Also the inlets on the front cylinders go straight into the crankcase and the rears go into the barrels. However I was using six Yamaha Banshee barrels which have all the inlet reed blocks and manifold rubbers in the barrels. As I had found with the RD750LC project there is no way that you could fit all four carbs into the V between the cylinders. It would have been possible to use the angled RD500 manifolds but the customer was building a YZR Grand Prix replica so he insisted that all the carbs were in the V. I tried many different ways but it was impossible, Ian (the customer) and I made a compromise and I made two inlet manifolds each which fed two cylinders, each with one big carb. They were a nightmare to design and make and here I was looking at making manifolds for a six cylinder! The RD750 V4 manifolds took a long time to make and I wasn't that happy with them. I think it is important when taking on a project to know when it is time to admit that a certain part of the job requires farming out to someone who would make a better job of it. The six