What's causing GSX-R1000 gearbox issue?

Q. I have a problem with my GSX-R1000 K5 selecting neutral when the engine is warmed over 75°C. All the gears work OK, it’s just when clicking into neutral that it won't come out of gear, without some coaxing back and forth between first and second.

I've been running the same fully synthetic oil for years and am at a loss as to what the problem could be. When it’s cold it’s fine. Any ideas?
hansie, MCN forums
 
A. It sounds very much like clutch drag. If you put your bike on a paddock stand, start it up and click into first gear with the clutch lever still held in, if it’s cold you will be able to stop any rear wheel rotation with your hand, but once the clutch plates have warmed up you won’t be able to stop it.

What’s happened is that some or all of the clutch plates have distorted. There’s a mix of friction plates and plain steel plates and the first step is to get the plates out and check for some twist in the steels using a flat surface like a pane of glass.

The friction plate checks are different, here you are looking for evidence of wear, overheating or slippage. If the friction material looks like it’s been smeared across its surface by slippage, it’s time to change them, especially if they smell burnt.

You might think you’ve been giving your bike a nice ‘present’ with fully synthetic oil, but unless it’s a JASO recommended 10/30 or 10/40w oil, it could have impregnated the friction plates, contributing to your problems.

Use a good quality semi-synthetic instead, and make sure you soak the friction plates in the new oil for a few hours before fitting.