jon next time your online please could you adress my post you seem to be the cluie one thanks im in oz im a pom too please help cheers orangutan.
Gday mite !
Thanks for your request - hope I can help.
Ok- I cant see the bike myself (Oz?- I wish!)so i'll try and describe the problem first, but if its a different prob, just mail back and correct me -
- There is 100% no drive at the wheel, i.e. you run the engine put it in any gear (not just 1st gear) and let the clutch out and you can stop the back wheel with the brake without stalling the engine.
(dont do it too much- you'll make the damage worse!)
I assume you were riding it one day and it just went?(could be a different reason if it was rebuilt then it didn't work)
OK - look at the countershaft sprocket first just in case (I'm sure you already did this)- Is it worn round and smooth? Take it off - are the splines on the sprocket and output shaft in good order?
So - delve deeper - There are quite a few posibilities (list at end), but my first instinct is the primary drive gear on the RHS of the crankshaft. Its held on with a woodruff key (a little half moon bit of metal). If the nut holding it on loosens a bit, it can move around enough to shear the key (especially on a 125 where you feather the clutch a lot to drive out of turns). The engine would run perfectly but transmit no drive to the gearbox.
So - take the full LHS casing off (OK engine in frame)and take off the nut that holds the gear onto the crankshaft.
Its tight so I normally use a wedge of pine between the primary gear (on the crank) and the clutch ring gear, but that wont work if its sheared so if its still tight you might have to take the barrel and piston off, make a nice flat block of wood that fits over the crankcase mouth (leave a gasket on it to avoid damage), and put other blocks either side of the con rod running front to rear that the gudgeon pin can bear on when you turn the nut - sounds complicated but is really easy.
Take the nut and gear off - if its the woodruff key it will be obvious - chopped and smeared. Clean the keyway up - if its not damaged (widened and uneven) count your lucky stars, chuck in a new key, tension the nut up correctly and you're back in business. If its burred, you can put a new crank in or have it built back up with weld but do not be tempted to weld the key in, or the gear to the shaft - it wont last two minutes and then you wont be able to get the crank out of the casing !
Anyway - I spent a lot of words on that - if its not that, check the rivets that hold the clutch gear to the back of the clutch basket, and also that there are enough clutch plates in. Also check that its really going into gear - if one of the pins that hold the selector forks snaps, it will click up and down but not really go into gear.
Good luck - let me know what it was when you find it.