Hello Jens,
The number is a bit funny, but crankcases could be 1976 RD350. As the clutch is wet, it has not straight-cut primary gears and as such the gearbox will also be standard I think. But it will be difficult to find a TZ gearbox, sidecover, dry clutch and primary gears.
TZ250 pistons are also hard to find so better make a list of what you want to do with this motor. Then I can give you advice of what to do !
Kind regards,
Ludy Beumer

Tack sĺ mycket Ludy-San! (keepig it a bit Swedish as well as Japanese)
Maybe you remembered my complete rolling TZ350F-chassi.
I was hoping to build two motors for it eventually. One for the swedish formulaLC (250lc _base_d engine ) and another for a faster forgotten class where tz350s runs (think I will use a rd350LCYPVS motor). In the formulaLC it´s possible to run TZ-top ends/clutch/gearbox on RDLC-cases. Was not going to (regarding the costs of buying and replacing TZ-stuff) but now this bottom end, cylinders and top showed up with new pistons...
And with them a third class emerged. It would be possible to run the aircooled rd-cases/TZ-top end amongst TZ250s in the "little forgotten class" in Sweden.
Compared to a tuned rd250lc top end would I benefit something running a TZ-top end ( in terms of power?
(I´m thinking peaky, expensive engine with rd-gearbox - problems keepin it in the powerband)
What would you go for if you where me? ( I have 2 or 3 RD350LC engines, 1 complete, tuned 350YPVS engine, Swarbricks, Mikuni 34s + 1 bottom-end. No TZ-engine parts or air-cooled rd stuff)
/Jens

You will benefit something like you said, Jens ! But in all fairness: a real TZ is a very quick bike indeed, half a TZ (or 75% TZ) is not much faster than a very good tuned RDLC. You do know that from the guys in England I think. And crankcases from RD250/350LC models are different from the TZ's. I would try to purchase a complete TZ engine somewhere.
But if this "mix" is cheap, it is nice to have for an experiment and see what you can do with it. Thata is all I will say. The rest is to other Forum members, please!

I will do that. If I get it I´ll give t a try it. If it´s not possible to run it with rd-gearbox I´ll try source more tz-stuff or pass it on to the pure tz-guys.
/Jens