Topic: help.... gearbox problems!

[daniel son]

having trouble with my 79 cb650z,  went out today for a ride and whilst giving it some in fifth the whole bike jerked like the clutch slipped and then caught again about 2-3 times so i backed off adn slowed down. i dropped into fourth and everything was fine so i changed up again but it done the same thing!!

basically, anyone have any idea what it could be??
i have replaced the clutch last year and the springs and all is well in 1st-4th gears. the problem is just in 5th.

anyone?

[mystic_1]

Are you sure that 5th is engaging fully?  I'm not familiar with the 650 but I know that early 750's do strange things sometimes if you end up "between gears".  Did anything feel odd about the shift action?

mystic_1

[daniel son]

nope, its shifts up as normal and everything feels ok and will cruise ok at about 1/8th throttle but anymore and it will jerk and jump but doesnt jump out of gear!

[mystic_1]

Hmm that sounds like a slipping clutch, but why it would do so only in 5th gear 

mystic_1

[daniel son]

i know, it will rev straight right round to the redline in 4th from about 40mph if you just open the thottle all the way. i will see if its any better when cold if not, its split the casings!
can you just remove the lower half of the casings and leave everything up to in place?

[kghost]

5th gear is the highest gear.

Thats usually where the slipping starts...high gear

[mystic_1]

<smacks head>

'doh, right, that whole "mechanical advantage" thing.

Friction plates are worn out.

mystic_1

[daniel son]

i think i will check the clutch first. when i replaced the clutch plates i didnt change the metal ones, so i will try them and check the friction plates as well. is it likely to be a gearbox problem ?
i have just changed the oil as well.

[shoemanII]

how many miles on the new clutch?  i figure it's kinda hard to wear one out that fast.  you didn't happen to change oil brand/type recently?  sure the adjustment is ok?  no offense, just wondering about other possible causes.
bobp   

[kghost]

I couldn't bring myself to ask the O question....

[eurban]

OK, I will . . .Are you using an automotive type oil with energy conserving friction modifiers?  There is a good amount of evidence that at least in some cases this causes clutch slip issues.  Also, before you pull the clutch apart make sure that you have a free moving and properly adjusted clutch cable.  Make the proper adjustments first at the set screw underneath the engine cover and then at the free play adjustment nuts on the cable.  Make sure that you have the return spring installed underneath the engine cover as well.

[daniel son]

i have just changed the oil last week, and im using automotive type oil but as far as i know it doesnt have any friction modifiers in it. i asked for minerl based oil and its 15w40.i did change the oil brand after the top end rebuild, buthave done 500 miles on this oil with no probs, i just changed it again after running in coz i  put new rings on, with the same oil.


i have only done around 3000 miles on the new clutch surely thats not enough to wear one out?

the clutch cable is ok, to test to see if its the gear at fault i was going to try riding in fifth but keeping my foot pushed up on the lever to stop it jumping out if that is the problem, do you think that will work?

[daniel son]

i checked the clutch adjustment on the bike again today and tried riding when the bike was cold, but it still does the same thing.

i tried holding the gearlever up in fifth but it didnt help

i do think it is gearbox related not clutch though, as when it slipps if you rev it, it will rev out like clutch slip but you can hear metal on metal slipping. sort of like when you dont push the clutch fully down and try to shift on a car....

any suggestions?
anyone had bad problems with a honda g/box?

[hapsh]

i have just changed the oil last week, and im using automotive type oil but as far as i know it doesnt have any friction modifiers in it. i asked for minerl based oil and its 15w40.

From what I know almost all the newer automotive oils have the Friction Modifiers in them.  You have to specifically get one that does NOT have the modifiers in them, IE Motorcycle Oil.  Post the brand and type up here and we should be able to confirm.

[turboguzzi]

honestly, cant see why a clutch problem will happen only in 5th. fully gassing it in 4th, maybe uphill, should yield the same simptom if its the clutch. Another quick test would be trying to do a short burn up, if it spins the tire you can be pretty much sure your clutch is fine. jerking and catching up again is usually more related to worn engagement dogs / bent shift fork. While doing my 500 motor this winter I found some serious wear in the 4/5th  gears dogs, resolved by sending for undercutting. the 500 & 650 g/box are pretty similar (save for the separate middle shift fork)

Test your clutch again though before heading for the big job of opening the cases.

And yes, you could leave the top end alone, turn over the motor and just open the bottom case. 
TG

[daniel son]

rite thanks for the info, turboguzzi. i will try burning the rear up. im sure its not the clutch.
with regards to splitting the cases, i was looking at the bike yesterday wondering whether or not i would have to even take the engine out at all, i reckon i can remove the bottom casing with it in place! but i will be working against gravity with the insides!

its funny how the top gears wore on yours turboguzzi, i would have though the first couple wouyld have been the ones to go first. if it is the dogs on 5th, how do i fix this, replace 5th gear or can it be saved?

[turboguzzi]

forget about doing it with the engine in the frame, no way. You need to split the cases, not just take the sump cover off.

I sent for undercutting since I am racing, but it could be also a solution insted of changing the gears. depends on how far they are gone. another option could be hard welding and reshaping the dogs. not sure it will be cheaper than new parts.

Also check the shift fork for wear/bent

dont get offended, but seriously evaluate your skill level as splitting the cases and more so, closing them so they are oil tight is pretty advanced stuff. lots of room for things to go wrong. you will want to do all your seals while you are there.

TG

[daniel son]

it was just a thought, im always trying to find a n easy way!

i will find some prices for new gears, i think i saw them on david silvers for a round £30.
i will check the fork for wear, do i just chek the ends of the selector for wear or am i looking for somthing else as well?

oh, no offence taken, im glad for the warning. my day job is an auto mechanic and im starting a new job going onto bikes in the next couple of weeks so there will be help if i need it!

i will do the seals while im there

nice
dan

[kslrr]

It sounds like a worn 5th gear shifting fork.  The dogs are not engaging completely.

[daniel son]

i will have a look at the fshifting mechanism and selctor drum, thanks to Hondaman tomorrow, i just hope its something easy to fix!
i will keep you updated