Thanks Mark

Finally I've split the crankcase, a couple of resistant screws needed telling. 

Attached are some initial images, I'll remove the gears to check out the shafts closer.
 interesting that the bearings came out also. And no shims evident on shaft ends.

Thanks for your help

 

Something unusual going on there if its an RT2 as i can see the early selector drum with selector wrapped around the drum. Also don't loose the small roller things that sit on selector pins--i see pin with one missing. If its an early trans it should have coarse teeth, or was that just DT1--i used to mix n match everything. Watch out for the thin shim when you pull the big bearing as it holds the two half circles from falling off the shaft.

Thanks Mark, yes my same thoughts its an RT1 gearbox in there. I have the pins. Once I have removed the bearings etc and have all the componants freely to hand - what wear am I looking to assess and where am I looking?

Surprisingly from looking at the pics the dogs look good & not round edged & selectors don't look bad either. Back to school for me..

Another update for anyone still following this saga :-) I've been splitting my time between the workshop and computer. I've found (possibly) that it actual has DT1 selector forks and a RT cam shift......

That's strange--what i wrote in post #25 is still sitting in the message box, like not posted, a day later. But is posted. Not important.

Anyway--RT1 never had the wrap around 4th-5th selector & drum setup. So in my opinion you have a full early DT1 trans. Sort of thing i used to do but the 360 used to blow 3rd gear wheel into pieces motocrossing. Loved the ratio spacing despite weakness. Blew it on my DT1 too, & came out the bottom--uhh, bugger. If i'm right then you have the coarse tooth DT1 trans complete, in which case there will be an empty selector shaft hole in you RT2 case where the 4th-5th selector shaft ran in a full RT2 trans. Also RT2 had the fine tooth stronger gears right from the start. Think DT1 upgraded to that in "70, maybe "71 but all academic as you have what you have!!. Sure it a 360 motor? & not a DT1 250--Had to ask & sorry for being smart arse.

Hiya. I think you are right, I've had a close look and DT1 seems to be the flavour of gearbox within the RT2 cases. 
I'm no closer to working out what the problem could have been though. 
I wonder if the kick idler gear going awol could have been floating on the shaft and jamming. It obviously took some severe force to shesr the shaft at some point, 

But if so, I wonder why it showed in 3rd only....


But yes defo a 360 - I have RT2 and RT2 MX cylinders & heads.....

And nope, not a smartass - v helpful - thanks 

OK, so I've had a forensic look at the gearing, counting teeth etc and this thing seems all over the place. Its not a full set of DT1, RT2 or MX gears.
On the main shaft (to clutch) there is even what looks like to be a pinion and wheel the wrong way around order wise....

SO we might have the problem nailed.

Can anyone provide a totally reliable guide for what should be in there, DT1 wise
I have a diagram via CMSNL which I'd like to double check against.

Many thanks

Probably no help but just for info--on those first coarse tooth dt1 trans there's two sets of gears identical on both shafts. So when the dogs gets rounded off & trying to get out of gear, we used to swap them over on the shafts to get the relatively undamaged side of the dogs & dog slots working & all good again-till next time, then ya realy in trouble.