Hi.
For those who want to know how to disassemble the gearbox, the pinion must be heated to about 200ºc.

Now I'm going to change the bearings.
They are references of Gasgas.
MT280236158
MT280232043

Cheers.

Edited August 28, 20187 yr by papapitufo

17 hours ago, papapitufo said:

Hi.
For those who want to know how to disassemble the gearbox, the pinion must be heated to about 200ºc.

Now I'm going to change the bearings.
They are references of Gasgas.
MT280236158
MT280232043

Cheers.

Looks like you need about £200 worth of clamps and pullers as well as a good heat source?

oh dear.

Please keep us up to date with your gearbox work.Controlling the input from the resident troll is as easy as clicking the "report post" button.

3 minutes ago, ric h said:

Please keep us up to date with your gearbox work.Controlling the input from the resident troll is as easy as clicking the "report post" button.

Please re-read what was stated. We all have ways and means to carry out difficult tasks and my observations if you feel they were out of kilter then feel free to “report post”. As for resident Troll I feel that was totally uncalled for. And as papapitofu posted some very useful photos and it’s their post let them decide about your suggestion??

2 hours ago, section swept said:

Please re-read what was stated. We all have ways and means to carry out difficult tasks and my observations if you feel they were out of kilter then feel free to “report post”. As for resident Troll I feel that was totally uncalled for. And as papapitofu posted some very useful photos and it’s their post let them decide about your suggestion??

Hi.
It does not say it for your comment, it is for another user.
Pleased to show you the repair process.
Greetings.

@ric h I am not trolling. Clearly any kind of post about Ossa gearboxes should come with a health warning, or at least some kind of justification of why you would even post this without any kind of reason or purpose?

Edited August 31, 20187 yr by nigel dabster

Hola papapitufo, creo que fue muy amable de su parte el tomarse el tiempo para mostrar como se desmonta el eje primario Ossa, gracias. Lo siento si mi espanol gramatica es un poco malo. En ingles....The pinion at the end of the shaft is a very tight interference fit, and pretty good for about 3-4 disassemblies. With a bit of heat, you can use a standard Toldeo type bearing puller, I don't have anything as hefty (fuerte) as the puller you are using. We made a few modifications to improve the oiling around the gearbox, particularly to prevent the kickstart idler gear sleeve bush (casquillo de pinion intermedio) from premature wear. We drilled an extra oil feed hole through the inner gearbox plate, directly into the bearing. I experimented with different bearing materials, there was not a lot of options, for this bush, and ended up making a Delrin sleeve to replace the teflon lined bush. When the standard bush wears, it allows the secondary shaft to have a lot of axial play, which was accentuated when in second gear (the gear farthest away from the bush). This play was the cause of the whining gear noise when in second gear, as the bush wore out. If I can find a spare gearbox inner plate with the mod, I can post a photo of this mod, if interested. Saludos, Peter B.

This is great information, papapitufo! Thank you! I have a question and an observation.

How do you remove the secondary shaft (where the drive sprocket attaches) to get to the point shown in the first photo? I see two inaccessible snap rings, and that's all.

I believe there is an error in the second bearing part number. MT280232043 appears to be a Torrington bearing for the “clutch pump piston” (OSSA equivalent 173002RA). I think we actually want to also replace two MT280432039 (30x33x10) bearings while everything is apart. These are the bearings on which the clutch basket turns.

Edited December 3, 20187 yr by konrad
transposed two words

Hi.
You have to remove the circlip with two fine-tipped screwdrivers. It's a bit difficult but it comes out, then you slide the pinion down, and it would all come out.
Greetings.

I now see 3 circlip locations, but none look like they would allow any gears to then be removed. 

Much more information here: https://www.ossa-efi.com/home/engine/gearbox

Edited January 4, 20233 yr by konrad

You need to remove number 2 by sliding it along a bit at a time (poco a poco) which allows the secondary shaft to wriggle out as you fiddle with the primary shaft, moving the primary shaft gears to allow the secondary shaft to be removed. With the secondary shaft removed, you then have access to the kickstart idler gear stub shaft, held in by a circlip and a shim behind that. With careful manipulation of the primary shaft (you don't need to remove it to get the stub shaft off) you can gain enough clearance to remove the stub shaft. Even when new, the primary shaft clutch basket was pretty sloppy. Bye, Peter B.

Peter, that was hugely helpful! Thanks a million!  I never would have "guessed" that solution.  Here's a pic for the next poor ******* who has to tackle this problem.

The grey screwdrivers eventually worked.  The red and green were too small.  It helps to have the gearbox held rigidly (I lightly clamped it in a vise) when first moving the circlip.  I had to progressively move the circlip along the shaft as more and more wiggle room became available.  Eventually, everything just fell apart.

I tried the pallet knife shown between the circlip and the adjacent gear, but it was not helpful.  I removed the circlip completely as I did not want it stretched while I wait for bearings to arrive.

Edited December 7, 20187 yr by konrad

Looking at your photo, the first gear on the left is 1st gear. On the early bikes, this can cause a problem as there was insufficient oil feed to the bearing surface that only became a problem when belting along in 6th gear. The 1st gear is being rotated on the shaft when 6th is engaged, or driving, so you can understand that it is rotating pretty fast when you are in 6th and getting a move on. Due to a lack of oil, heat would build up and ultimately the 1st gear could seize. While there is a small oil hole on the shaft bearing surface, there is only the clearance between the gear and shaft to allow oil to access this area. We modified this by machining a spiral type groove across the shaft bearing surface to allow for an oil feed path, which worked. Later models, had a spiral machined into the first gear which did the trick, and had a larger oil hole in the shaft. Bye, Peter B.

Does anyone have any pictures of where PeterB is referring to? I figured since my gearbox is out to be repaired I may as will do the mods to help increase the life of the bike. 

 

Thank you