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Your  RD and LC racer tips

Racing a converted LC or RD Yamaha is a hell of a lot of fun. They respond well to "hotting up" and can be quite competitive with the TZ's etc. if done right.

This is a collection point for race tips from contributors. Why not write down what you've done to your bike  (that you find works for you) and email it to the webmaster for inclusion here?


Contributors:


Rob Bunyan from South Africa writes:

"Over here we run LC's in vintage Superbike against anything and everything of the era (Ducati Pantah, Suzuki Katanas, etc. and are allowed to do anything we want to the motor. Some things I have done which you may or may not want to include:

 If capacity increases are allowed- use IT200 pistons which have lovely big windows, take it out to about 375, are much cheaper but are shorter from pin to crown, so you need to machine the bottom of the barrel. We took 1mm less than required off the bottom and the rest from the top to effectively move the transfers up a little. Another alternative is to use 2mm o/s Banshee quad pistons which drop straight in with no machining except the obvious rebore. Dropping the barrels may cause clearance issues when trying to fit the exhausts but a little grinding on the flanges sorts it out.

We use Pro-X pistons in this bike and in our race 50s. My 16000rpm 160km/h 50 (RZ50 motor in RG50 chassis) has done two  6 hour endurance races and a season of sprints without the head being lifted.

Crank: We used a power valve crank with banshee big end bearings for more reliabiliity. A local machine shop buys up bearings similar to the mains with the groove in the outer race, and spark erodes a hole and inserts the pin to copy the Yamaha main bearing design for a fraction of the cost.

Ignition: My engine builder is also an electronics guru, and he also tunes 50cc racers. He fits MX ignitions to the 50s, therefore he has a large box of 50 ignitions going nowhere. He machines up a backing plate to fit a Honda MBX50 baseplate- the smaller diameter flywheel fits straight onto the LC crank, and being a 4 magnet flywheel it is very easy for someone with his skills to build a CDI to fire a twin. The result is a pickup like a MX bike and no heavy retardation at 10000rpm that you get with the stock system. We also suspect that the crank pin problems that LCs sometimes have on the left pin are the same as we see on high revving 50s with stock flywheels- the inertia twists the crank out of alignment and the pin snaps.
He also includes an electronic rev counter pickup in the box to allow a modern rev counter.

Brakes: I fitted an RZ50 master cylinder which has a smaller diameter- more power, more feel, more lever travel. It feels spongy even with the braided hoses, but when you're rolling it's fantastic. Also using power valve calipers which bolt straight on but may not be allowed under some rules.

Other stuff: We have modded a stock airbox but it is as yet untested. If we get good results, I will describe what we have done. We also dropped the inlet port quite a bit. The bike is brand new, built for this year's racing season, and is currently being tidied up, painted, tuned, etc. I will keep you posted and send in a photo when it looks like something.


Cheers,  Rob Bunyan,

Capetown, South Africa "


 

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03/23/08 10:32 AM +1000    

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