When you get it sorted please be sure to fully tighten the mag flywheel because if it shears off the crank key then this sort of thing can happen with kickback or even worse if it starts & runs backward then you accidentaly touch the kick lever & running backwards just drive the kick stop where it can't go & splits the cases. Sorry if that's laying it on thick but have seen it happen.

imgur.com/a/PO621l0

ok..so we have a bent shaft then
off to the parts catalouge again then

also anyone here able to advise if any if any of these can remain in pace before splitting the cases pls?
imgur.com/a/NzDdbzJ

only to save tme and possible burring of screw heads
have an impact driver though

You will need to remove the oil seal retainer plate to change the seal, and might need to loosen the gear indexing pin, if the gear indexing needs to be adjusted. The pressed steel plate on the end of the selector drum can remain, but you will need to remove the detent wheel.

Its well worth making a wooden cradle to rest the motor on while you are working on it. A case separator tool is a good idea, but cases can be split without one. Very good idea to find the reason why the output shaft is bent, and carefully check the cases arent cracked. 

What generally happens when there are kickstart gear issues, is the spur gear on the back of the clutch drum gets damaged. Never seen one with the shaft destroyed before? 

Don't mess with the eccentric screw at bottom center.  Does not need to be removed. And almost never needs to be adjusted.  It can be a PITA to get correct. 

Shift drum can stay as-is too...  you do need to remove the three screw cover, retainer, and shim on the other side of the engine.

Seal retainer does not need to be removed to split case but obviously does to replace crank seal so might as well do it now. 

Do yourself a favor and use a two bolt puller to press on ignition side of crank when splitting case.  There are two 8mm threaded holes in case under stator plate for this.  Center bolt on puller presses on end of crank.  Many auto parts stores rent a two bolt steering wheel puller or equivalent for free. 

It's very easy to adjust the gear indexing screw, with a very simple checking tool made of an aluminium welding rod. When a motor has destroyed the output shaft, and this has to be replaced, the whole gearbox must be carefully checked and any damaged parts replaced. Indexing, being out of adjustment, can cause issues, so it's always worth checking if any major work has been carried out.

To check the gearbox, the cases can be split without the case splitting tool. Remove all the crankcase screws from the LH side of the motor. Then place the motor flywheel face down, on a rectangular wooden cradle.

A few light taps on the drive side end of the crank, while supporting the RH crankcase half, will almost always mean the RH case will come off easily. The gearbox remains in the LH case.

The cranks are a much tighter fit in the LH case, and if the crank bearing is being changed, will need to be removed with a press, or case separator tool.

Gently heating the bearing inner race, is one way of putting the crankshaft back into the LH main bearing, but making a tool along the same lines as the factory one, makes the job easier, and is well worth doing if there is any intention to rebuild more engines.

I made one out of a piece of aluminium scaffold tube, an old flywheel nut, and a 10 mm threaded rod. With different adapters, it works on pretty much all single cylinder 2T motors, and is a useful thing to have. You can probably buy them, but might be quite costly?

imgur.com/a/HpRCusW
finding the shift drum wont budge unforutnately so will leave in situe?
couple of stubborn crank screws also causing me worry,hope dont need to drill out they are getting close to not having any purchase left for my impact driver
have made a crank case splitter with some uni strut 2 x 8mm bolts and using the flyweheel nut to ease it off
have left it for tonight as was getting flustered

If you have a MIG welder, put blobs of weld on the stuck case screws, and turn them out with vice grips, when the weld is still red hot.

It's not possible to remove the shift drum with splitting the cases first.  Take the RH case off the LH case, leaving the crank and gearbox in the LH side.

It is possible to take the LH case off of the RH one, but there is no advantage to that, as you are simply making things more difficult for no real reason.

got lucky with the shaft at least
£20
NOS (apparently)
imgur.com/a/YFWqbTy

Wrong shaft i'm sure without researching. Thats the main shaft the clutch sits on. I'll link the parts page.