Hi all
unsure exactly whats going on here  but to try to summarise an issue i am having with my DT175 76 twinshock if i can
basically it started but wouldnt drive, no power, just about ran but died easily
did idle & start ok however
chenged the plug cleaned carb and it got me home
then started kicking back on kickstart quite nasty
which resulted in the whole kick start siezing, wouldnt budge, took head off no damage to piston, rings or reeds, gave it a boot with head off and it freed up,
so far have changed LH crank seal, (was blown out completely well destroyed really and had to pull out bit by bit) new crank seal, new woodruff key (it has now sheared two but likley my fault not torquing stator up properly) drained oil checked kickstart and damage to idle gear teeth, i think it kicked back vilolently and damaged it, put it back together for now with old kickstart ide gear just to see if a new ignition coil would help (not the issue) since then the kickstart wont engage now, engine feels really stiff with plug in (not with it out though) and another woodruff key sheared
what could be causing the sudden timing issues and kickback? condenser perhaps? the kickstart i can sort with a replacement idle gear if i can find one just need to get it running right on timing and try to understnd why the sudden timing issues , have a point checker and diial guage on way to set points
any advice greatly appreciated D

You will need to remove the clutch cover. The kickstart stop has probably moved on the kickstart shaft. On TY175s, that results in a hole through the clutch cover, and sometimes damage to the kickstart gear on the back of the clutch.

If the oil seal is badly damaged, the main bearing might have broken up. Take the cover off and check.

thanks got it apart again and reseated the kick seems to be ok for now, once i realized the spring goes into the recess,  i will look at it again once i can fathom the timing issue shame i cant post photos currenty as not sure whats going on with the LH crank seal as i looked as if seal was still there as it was black but when i went to stck a screw in it so as to pull it out it was screwing into metal so deduced the seal had completely gone couldnt see  way of getting to the bearing or removing the bearing plate to see behind but the crank isnt moving so no play at all so hopefully bearing is ok until i can rebuild it over the winter, just trying to get the rest of the summer out of it before then hopefully 

Seal is metal coated with rubber. 

Most likely is key sheared first causing kickback.  The only other things I can think of is the timing advance mechanism under the flywheel came apart and points cam has moved out of normal range or someone adjusted the points which can advance the timing. 

You can post photos using Imgur or other hosting site (free) and linking them here.

Oh, and there isn't normally anything behind the seal that would prevent you from seeing most of the crankshaft ball bearing.  Not sure what you mean by "bearing plate"?  It's possible someone has done something "incorrect" like installing a sealed or shielded bearing?

Only you can see what you're looking at, we can't. 

imgur.com/a/PpbsEDL

ok so pictures seems an ache,not sure this will work but essentially when i came to change the crank LH seal i usually do this by srewing in a screw to the face of the seal to be able to get purchase on it however when i tried to do this it was like it was metal this time, so if seal has a metalbase its likely part of the seal face remains on the crank?
i will have to look again tomorrow as have another seal i can try if i can get the old one out
 

Has the main bearing cage broken up & destroyed the seal. If the cage broke & balls got confused [say no more] then cage bits could get under the flywheel & more. Ok that's stretching the imagination a bit. I'll go read the story now.
I guess the broken key started all the kick back problem & damage. Does it have a built in advancer in your flywheel as that's another point of interest.

imgur.com/a/kZxAbYA

yeah has timing advance govenor in flywheel
i have new woodruff key, tdc dial and points checker on way so can set points once back togrether
i think you have to hold the advance open through the hole to do it though?
the seal is odd as it totally looks like hthe whole seal has gone and am looking at the seal seat but understand should be ableto see the bearings under it?
 

Yep gotta hold it advanced.
Actualy there might be a small hole to insert a pin that locates the arm to hold it up.
Yamaha would make it easy wouldn't they--but maybe not.
Here's a similar flywheel og the net that shows a hole so i bet it lines up with a hgole in the flywheel.
If so then whatever you use you might have to toggle it to get the last bit of advance unless its a perfect fit & there's no wear in the moving bits right back to the cam where arm engages.
Of course i could be totaly wrong.
photos.app.goo.gl/xHeYWxwQAkDqVkgu8

Was the first photo taken before you replaced the seal?
The seal in that photo looks like it melted in the inner lip where it meets the crank or there is some type of sealant oozing out.
Crank taper and flywheel look quite dirty in the photos.
I would remove the woodruff key and lap the flywheel to the crank.
Make sure you clean it up afterwards removing all the lapping paste, it wont grip well if there's any dirt on the tapers.