4t jammed gearbox

[thall1]

So casings split… nothing obvious that’s broken or damaged. 
Using an Allen wrench on the gear change drum on the clutch side I can get 1st, neutral and 2nd… and there it stops?

always had a problem when going 2nd-3rd it felt like 2nd hadn’t fully disengaged but cleared if I went back to 2nd the up into 3rd… 

lovely & clean inside.. no debris or any sort to be found which in some respects is very good but was hopping to see something obvious and maybe something sat in the bottom of the casing!

any thoughts would be greatly appreciated!

 

[lineaway]

Did you have a shift shaft problem first?

[lineaway]

You do know that you have to spin the shafts to get them to shift.

[thall1]

Yes, I did snap the paw from the gear selector shaft. I welded it back together, making sure it was exactly the same position from when it snapped, also made a new paw slide pin as mine had quite a bit of wear, you could move the lever quite a few degrees before it actually started to turn the gear cam. Gear change was brilliant after… I could select every gear with ease, even found neutral with the engine running!  ( I can’t upload a photo atm… file to big-don’t know why?… perhaps I’ve exceeded my allowance?)

everything was great until the bike went down on its left side onto rocks. After that I had a lever that didn’t really do anything but unlike when I snapped the paw assembly off the shaft and the shaft would just move excessively up

or down as far as the bash plate, it didn’t seem to have full movement… after quite a few tries I got 2nd and left it there…. At first I assumed I’d snapped the shaft again or something related to it …There were no strange noises or anything to suspect gears were eating themselves.. and no signs of that now it’s apart… my son rode the bike for a while and he too couldn’t find anything bar 2nd. He got neutral a few times.

and yes I’m spinning the shafts while trying to change gear using  the indent cam.

im at a loss now!?

[thall1]

Just to add… the gear selector drum is virtually unmarked… and the pin the locates it in relation the the ident cam is also unmarked.

[lineaway]

 

The shift shaft would break loose at the weld. You did check that?

[thall1]

Yes that was my first thought that it had snapped again but it’s fine hence why I’ve now stripped the gearbox

[lemur]

Check the shift forks for slight bends or wear on the tips or binding on the shaft.  

[thall1]

4 hours ago, lemur said:

Check the shift forks for slight bends or wear on the tips or binding on the shaft.  

That’s my next plan… the shafts are fine and they don’t bind on them.. I was going to put the shafts into vee blocks and check the squareness of the selector forks. Initial inspection shows nothing up.. 

[lineaway]

I had just assembled a brand new 1995 Fantic section that would not shift at all. After a couple of days of checking the easy stuff I split the motor. I found nothing wrong at all but a blued shift fork from forcing the shift. (Side note, it was assembled without a base gasket from the factory. Plus for the tear down.) Replaced all the shift forks and reassembled. That bike never, ever had another mechanical problem. Just goes to show not all issues are clearly evident. 

 You might fake putting the cases together to get that motor to shift through the gears before the final re - assembly. Good luck.

[lemur]

Logic I apply is that the shifter forks are the softest and most malleable parts in the transmission.

... and because I experienced the problem first hand on my 360VA

Edited 18 hours ago by lemur

[thall1]

Thanks guys…. I’ll take another good look at it all tomorrow with fresh eyes!