Topic: Replacing the countershaft

[MetalHead550]

Finally found a set of transmission gears to replace the bad countershaft in my 78 550k.  The engine is upside down and Im ready to split the cases.  All components have been removed: points plate/advancer, alternator, clutch, shifter linkage.  All bolts that can be pulled on the bottom end have been removed including the one hidden in the gear box and the ones that bolt from the top.  Pretty sure I got em all.  My Clymer manual does not detail a bottom end tear down, at least not starting from the bottom end.  Does the primary chain have to be removed to split the cases?  If so, can I do it from the bottom and how?

[bryanj]

Remove the plate partialy hidden behind the clutch holding the primary shaft bearing; Remove the oil pump and tap out the shaft whilst levering behind the primary gear with a tyre iron or big screwdriver BE CAREFULL YOU DONT DAMAGE THE GASKET SURFACE. Check all the oilways carefully for damage caused by the primary chain as there is no tensioner and the chain can eat the casings. Only cure is new chain and to do that the crank has to come out.
PS how or what is wrong with the coountershaft, these trans are normally bulletproof

[MetalHead550]

Gotcha.  Thanks guys!  Learning as I go, and its been great seeing a understanding how everthing operates.  I plan to know these bikes from the inside out one of these days...with the help of this forum of course! 

Bryanj:  Yes these motors are bullet proof but not fool proof as I suspect it was an unskilled rider that caused the problem.  The dogs on countershaft 4th gear have been busted off, all of them.  So as the fork pulls 4th gear into countershaft 3rd, there are no dogs to to grab it so mainshaft 3rd just spins countershaft 3rd as though you were in neutral.  Im guessing someone either downshifted to 3rd at way to high rpm or tried a clutchless shift?  Perhaps a combination?  Anyway the motor is solid and everthing else in the gearbox looks great but Ill check the oilways ect. when I pull the primary as you suggested. 

BTW This is my low budget, rat-cafe project that is going slowly but surely.  Forks, carbs, and breaks have been gone through.  Fenders have been cut.   Engine and frame will be painted once the motors back together.  Getting bars, tires (tyres), and a cafe seat made this winter. Then the tank and side covers will get paint in early spring...should be cool.  Of course youll see pics...eventually.

[bryanj]

There were acouple of mods on one of the gears and i think it may have been that one!  Be very carefull on assembly as the tooth profile and root diameter changed so its best to change gears as running pairs if possible. EG 500 dont fit and 650 look similar but only fit as pairs!

[MetalHead550]

Well the doner gears are out of a 75 550.  Counter shaft and main shaft with all gears intact.  Theres no difference between the 78 and 75 gears is there?  Will I still need to change them as set?

[bryanj]

Cant remember at momenr and cant get at parts books to check just now. If you have complete shafts and gears just drop the lot in It'l be easier.