Well, I did it now. Kicked over my RT1 and it fired up but the kick starter stayed down. That never happened before, so I was thinking maybe I broke the spring. Before I could do anything, the kick starter snapped back up with a loud bang (and yes, hit me in the leg, ouch!). Pulled the side cover and the spring was fine, but the stop on the starter had broke the tab that's molded into the case, and actually cracked the case between the 2 bolts there. I think the case is toast. Been looking for another right case and haven't been able to find one. Looks like the part #275-15121-01 is for a '70 or '71. There is another part number for '72 and '73 that starts with #291.

My question is, are these cases interchangeable? It looks like they might be, but it also says that it fits a DT1/2. I know that the studs sticking up from the case for the barrel are different from the 250 to the 360, but it seems like they have the same part numbers. Can anyone clarify this for me and point me in the right direction? Also, does anyone have, or know where I can get a right case? They don't seem to be anywhere.

Thanks,
Steve

250 case will not fit 360!  You are seeing an artifact of the "shared part list" migration to digital that has been discussed here ad nauseam. 

Part number prefix is critical.  In general, the prefix for a 360 case half needs to be a 360 "model code" which in this case is "275" 

("291" is a 250 prefix and should fit the 250 from 68-73.)

Just something to be very aware of--is--the early cases didn't have the hole cast for the selector shaft for the 4th 5th selector.
That's because 'that selector' wraps around the drum so no shaft required. Look at the link below!!
In saying 'that'--now i wake up--i guess it doesn't matter if a later case was used except the empty hole would transfer oil faster at oil changes to level it out.
I'll study the parts pics incase there's things i've not thought of.
I'm guessing yours has 'that early' selector system if original.
www.partzilla.com/catalog/yamaha/motorcycle/1970/rt1/shifter-1
Sorry, see next post.
Partzilla's giving me a headache & not always correct or easy to follow even though i can build these motors with eyes shut, mix & matching parts from different years.

Ok i think i'm wrong & only the 250 has that selector system!!.
It shows the 250 type in the small pic within the big pic.
Sorry about that chief.
Me Mr Know-it-all Not haha.

Try searching ebay item # 285984788915. Looks like a match for your part, plus you get the L side too.

RT3 Cases

This is a note about interchangability
www.partsfish.com/oemparts/a/yam/5241b6e...crankcase-notes-only

Wow, thankyou very much rsteve56, that's great searching & info to have.
& i'd forgotten the drive axle bearing on the right where the kick intermediate gear runs, had changed to a thicker outer shell bearing.

Thanks for all the input. PABDT, I did see those cases on ebay, but they have the part number starting with 291. They look similar, but I'm not sure if they will fit my '70. Does anyone know if they will fit my '70 RT1???

Thanks,
Steve
'70 RT1, '70 AT1, '70 CT1, '85 RZ350, '85 RZV500R, '70 Honda CT70H (part of the posse)

Didn't mean to mislead you.   I noted the partzilla (ha ha thats never wrong) parts crossover showed the case the same as the RT3. lots of smoke and mirrors out there on ebay to get a sale.  

 

Quote: "............PABDT, I did see those cases on ebay, but they have the part number starting with 291............"

This is probably going to sound harsh but my choice is either this or say nothing.  So don't read further if you are easily offended. 

On what are you basing your claim, stated as fact, that those cases have a part number starting with 291?  

291 is a DT prefix, not an RT prefix.  Ebay seller claims they are RT3 360 cases.  Part number listed in the auction listing starts with 275.  VIN stamped into cases identify them as RT cases!

(Don't buy them if you KNOW they are 291 cases.  But my guess is you either didn't read or pay attention to my post about the dangers of "shared parts lists" and are just incorrectly identifying the case part numbers because of a personal assumption you're making based on bad information you looked up someplace?)

Also pay attention to the post about interchangeability as the later cases will be the improved "-01" variants and may need to follow the instructions about the new parts you'll need to use the newer cases on your older RT.

P.S. PABDT, you didn't mislead anyone.