Gear shifting is extremely violent

[TheStigsIndianCousin]

Hi everyone,

So we're using a Honda CBR 600 RR engine, and we've been testing our car for about two weeks now.

We've noticed that whenever we shift gears (regardless of it being an upshift or downshift), we get an extremely violent reaction from the engine. To the point that the chain actually gets lifted off of the sprockets and hits the scatter shield. Also, the whole car lurches forward a couple of inches every time we shift in standstill.

The engine was purchased used (~5000 miles), but we've also had that problem on our spare engine.

Is it because of the crash-box type gearbox that the engine has? I haven't had any experience with this engine to speak of, so I'm completely clueless as to whether this is normal or something to be concerned about.

PS: another thing that I was unsure off was how you people determine how tight the chain should be? We've had our chain face severe elongation even after just a couple of shifts. Maybe we've got it too tight?

Any help, ideas, advice would be greatly appreciated.

Viren Bhanot
Drivetrain Head
Formula Manipal

[TheStigsIndianCousin]

Hi everyone,

So we're using a Honda CBR 600 RR engine, and we've been testing our car for about two weeks now.

We've noticed that whenever we shift gears (regardless of it being an upshift or downshift), we get an extremely violent reaction from the engine. To the point that the chain actually gets lifted off of the sprockets and hits the scatter shield. Also, the whole car lurches forward a couple of inches every time we shift in standstill.

The engine was purchased used (~5000 miles), but we've also had that problem on our spare engine.

Is it because of the crash-box type gearbox that the engine has? I haven't had any experience with this engine to speak of, so I'm completely clueless as to whether this is normal or something to be concerned about.

PS: another thing that I was unsure off was how you people determine how tight the chain should be? We've had our chain face severe elongation even after just a couple of shifts. Maybe we've got it too tight?

Any help, ideas, advice would be greatly appreciated.

Viren Bhanot
Drivetrain Head
Formula Manipal

[Adambomb]

Assuming you guys are shifting it right...

First thing I would guess is there's a lot of compliance between the rear sprocket and the engine, causing enough movement to make the chain skip. With a solid final drive mounting and good driver, it should shift very smoothly.

As for the car lurching forward a couple inches when putting it in gear, that's normal, most bikes will do that to some extent.

As for chain tension, seeing as how you don't have to deal with swing arm rotation, you can get away with having them pretty tight. 1/4-3/8" is what I usually shoot for. Any time you replace it there's typically a break-in period where you'll have to adjust it frequently for the first little bit. Although if it's skipping teeth that will make things worse.

[Auerbach]

Be sure the clutch is adjusted properly such that it fully disengages. I've found that bike clutches can be tricky to get in the right range because the plates usually do have some contact even with the clutch pulled (or pressed or squeezed or actuated, whatever your system). Also if the idle is higher than normal, it will exacerbate the problem.
Since you said this happens on your spare engine also, the lurching may be normal as Adambomb said, and you're just not used to it.

For chain tension, push down in the middle of the span of chain with your finger and it should deflect 1/4-3/8" as Adambomb said. Then go wash the chain lube off your hands.