T140 D (1982) Bought For Restoration.

@Ian Champ Yes mate i would say its the gearbox but get that old rusty chain out of the way. Try to select a gear remove the plugs and try the kickstart if it turns all good if not its gearbox.

 

@Ian Champ That's better news. The old chain plenty of wd or even diesel or fine oil for a few days if you can break it as close to the sprocket as possible. Engine turning freely could just be the clutch slipping so don't worry to much yet.

 

You could use valve stem lash caps 71-3748B to fix this, this will alter the angle at which the rocker meets the valve stem but seems to work well. The tappets will presumably also be worn, if replacing them I prefer the mushroom type.

Have you checked the valve stems and seating surfaces, these may also be worn? I recently replaced my valves as the exhaust ones were heavily pitted and grinding them was not making much difference, I picked up some NOS inlet valves really cheaply and LF Harris exhaust ones for a good price.

 

The kickstart turns the engine via the gearbox and clutch so a seized clutch will still allow the engine to turn when using the kickstart. It is more than likely that the clutch plates are glued together with old oil - you need a puller to remove the clutch which will also give you access to the drive sprocket.

Under normal operating conditions the clutch plates on these bikes can stick when the engine is not running. The starting routine involves pulling in the clutch and kicking it over until the kickstart moves freely with next to no resistance which indicates the clutch plates are free and no longer turning the engine. The bike can then be started after releasing the clutch.

Some drive sprockets have two threaded holes which allow you to use a two bolt puller to remove them, although they may also just pull out when the retaining nut is released. The problem here is the huge box spanner (not cheap) required to remove the drive sprocket nut and the high torque values required for the nut.

A word of caution, the gearbox output shaft is a common leakage point and the seals are difficult to access unless the clutch and drive sprocket are removed so it is worth taking great care on re-assembly to ensure that the seals are not damaged and the sprocket splines are sealed.

 

Have you tried applying heat?

 

Plus gas and heat.

 

Are you using a 12 point ring spanner? There are purpose made ones specifically for those type of nuts and the limited access. I appreciate that the correct size will be difficult to fit due to the build up of crud you mentioned unless you are successful in removing the crud first.

 

I sometimes use a short length of bowden cable in an electric drill to clean crud out of difficult to reach bits, including threaded holes.

I keep the cable as short as possible (too long makes it difficult to control) and wrap some gaffer tape around it, leaving approximately 1/2" unwrapped at the free end. The unwrapped free end of the cable splays out and acts like a mini wire brush and gets into places a conventional rotary wire brush can't reach.

 

@Ian Champ You know with all the peeps chipping in here with fantastic idea's it must make your pain much more bearable and you will be a winner.