Only 5th and 6th work

[Jaberwaki]

Last night on highway riding at 70 in 6th gear I give her a little more gas to pass and bike shudders a little. I was just riding to ride so I figure better safe then sorry better turn homeward and check chain to insure not slipping.. Found a safe place to turn around and start downshifting. Into 5th fine, gofor 4th._. Nothing. Try again and again but wont downshift thinking the clutch may have gone i try up shift 6th no problem downshift to 5th again no problem go for 4th._. Nothing no click try again 6th fine, 5th fine nothing below that. I learn again what a great engine builder i had juice up my bike because there are 5 lights on my way hom and i caught all of them on red but she had no issue pulling from the lights in 5th gear . Is there a known issue causing this? Something i can check at home before spend the cash at a shop to fix?

 

[Kiwi Rider]

First thing to look at is the engine oil and magnetic drain bung.
Drain the oil and see if you have pieces of metal attached to the magnet, or falling into your drain pan.
If none, take off the RH clutch cover and check that the shifter spring etc are all as they should be.
If all that looks ok time to remove the engine and open her up. Damn.

 

[bigoltool]

Shift linkage all tight?

 

[Kiwi Rider]

Shift linkage all tight?

Good point, basics MUST be checked first! Check the pinch bolt on the gear shift lever and the splines are not stripped at all.

 

[bigoltool]

Good point, basics MUST be checked first! Check the pinch bolt on the gear shift lever and the splines are not stripped at all.

I actually had this happen once after I re-adjusted the height of my shifter to work with my Buell pegs. Didn't have everything tight and got to an intersection and found myself struggling to get the bike into gear. If that's what is wrong its an easy fix.

 

[Kiwi Rider]

It's the same old story... ALWAYS start by checking the basics, then move on to the more complex stuff

 

[Jaberwaki]

Thank you for the replies so far shift linkage is tight as i said two of the gears work fine, double checked just to be sure.Kiwi it sounds like you turn wrenches alot on your ride. I can break a car motor down to the block and put it back with no problem but i have very limited exp working on my bike. The pinch bolt and splines is it possible for those to cause losing 4th and below but 5th and 6th to be fine?

 

[Kiwi Rider]

Thank you for the replies so far shift linkage is tight as i said two of the gears work fine, double checked just to be sure.Kiwi it sounds like you turn wrenches alot on your ride. I can break a car motor down to the block and put it back with no problem but i have very limited exp working on my bike. The pinch bolt and splines is it possible for those to cause losing 4th and below but 5th and 6th to be fine?

Yeah man, I've done a lot of work on bikes, and I'm a automotive engineer by trade, have been working on cars (mostly) as my job/profession for 40 years, seen it all.
If the splines are worn to the point where they slip, it is possible for that particular symptom to rear it's ugly head. Hey, ya just gotta check every part and condition of said part and leave no stone unturned to be sure.
Let us know what the outcome is mate. Keen to know.

 

[Jaberwaki]

Thanks alot man, are the splines part of the clutch assembly or the transmission? Sorry for the noob questions but as i said Im new to motorcycle repair

 

[Jaberwaki]

Anyone ?

 

[sixpack577]

Anyone ?

The only splines in the clutch are on the shaft that the clutch basket slides on to.
It can't be that, because if those splines were stripped, you would have other problems.
I've never heard of clutch basket splines stripping in any bike engine. I'm not saying it couldn't happen, but the basket teeth are what get damaged from abusing a clutch.
The plates cut ridges in the teeth and cause bad chatter on engagement.

It sounds more like a shift fork is bent or broken, and therefore the transmission cannot engage those gears.

 

[Jaberwaki]

Thank you for the reply. So each gear has its own shift fork? If so perhaps only 4th is bent stopping me from getting any lower than 4th ? How tough are the to get to and replace?

 

[sixpack577]

Thank you for the reply. So each gear has its own shift fork? If so perhaps only 4th is bent stopping me from getting any lower than 4th ? How tough are the to get to and replace?

No, not one fork per gear.
I haven't opened a busa transmission, but I think there are 3, which is pretty standard on a 5-6 speed engine.
The cases need split to access the transmission.

 

[Jaberwaki]

Got it.I dont trust myself that far with my baby.. Looks like its time to see a pro.Dammit

 

[sixpack577]

If you work on cars, you can work on bikes.
The service manual is here, as well as alot of knowlegdable folks.
The money you spend on a few speciality tools will be less than labor, even buying stands.
I've split many an engine case(just not a Busa), and they are all designed about the same. It is not difficult, aside from any mechanical fun, like stripped threads, or seized fasteners.

 

[Kiwi Rider]

Thanks alot man, are the splines part of the clutch assembly or the transmission? Sorry for the noob questions but as i said Im new to motorcycle repair

The splines I am referring to are the splines on the gear lever shaft, NOT the clutch.

 

[mabupa]

I don’t have much to contribute here, so I’ll let the experts do that, but I’m curious to see what you find to be the smoking gun on this one, so keep us posted.