Firstly, you need to download the free PDF Yamaha R1 ‘99’ workshop manual from the internet. Also i have noticed that on various blogs there seems to be confusion as to what the correct engine oil to be used is and as you will see, any good 20W50 multigrade motoroil is what Yamaha have specified. I’ve had a few Yamaha R1 '99' bikes and i am a professional engine builder specializing in BMW V8 engine reconditioning. I have also built a few of these engines, one of the most wicked carburreted motors around.
The problem I have on my present ‘99’ engine, is when I top up with oil, adding lets say 100ml or so or when doing a completely new oil and filter change, the clutch assy slips for at least 150-200 km's and then subsides, as they all seem to do.
I have now come to the conclusion that the ‘old engine oil’ that gets imbedded into the friction plates is slowly replaced with the new blend of oil i.e. 'The 100ml of top-up oil or by the completely new oil added when doing the oil and filter replacement. This alters the state of the oil viscosity and forms a kind of barrier.
I usually change the oil every 3 to 4000 Km’s, so I am very familiar with the symptoms on this particular bikes engine. The clutch plates only begin slipping from about 9000 RPM, or when I hammer the clutch to get the front wheel airborne, especially when it's very cold out in Johannesburg.
There is no substitute for a stiffer pressure plate that I know of. I was told that a Yamaha FJ 1200 pressure plate would do the trick so I ordered one. They both looked identical when inspected before fitting and it made no difference at all to the slippage. My first '99' R1 never had this problem and I made x2 new Yamaha OEM clutch changes on that bike, also just for interest sake, I usually clocked up about 10,000 Km's on a new clutch before changing again. The only assumption I can make is that the clutch baskets coil springs weaken? Presently I am building an engine which has only 8000 Km's on the clock, so we will see how that clutch assy performs.
Lastly, I heard that there is a clutch that is slightly thicker and apparantly what the guys do is fit two of these slightly thicker clutch and/or friction plates in the middle of the stack. The PDF workshop manual stipulates the min and max thickness of the entire clutch plate stack. To me this sounds like an option that should work. Surely someone has the answer to the problem, or is Yamaha selling us superseded kits that have actually been designed and tested for later model R1 engines?