My two stroke runaway experience happened yesterday late in the afternoon. I pushed the bike in  the garage for the next day. After things warmed up this morning, I head out to the garage. I noticed a fresh oil leak under the left side, of a fairly non leaking motor. That settles any doubt, of the problem. I pulled the magneto off, there sits the  seal popped out of the case. When I installed new seals years ago I used red RTV. This was probably not the best sealer. The seal was still soft. I reinstalled it. I used red Loctite. It says it is ok with rubber. I remember seeing an aftermarket seal retainer. It must sit between the mag plate and the seal keeping it from pushing out. Anyone ever seen this? Stan

Well spotted. If ya mag cover was oil tight you might still be kicking or looking. Did it runaway just before you parked it, or do you think it happened as it stopped.

Great job!! 

Yamaha made seal retainers as an option on the mag side for some of the early smaller bikes...  I don't remember them for the 250/360...  I might not have been paying attention though. 

I think eventually what they did on the mag side was design the stator plate to sit tighter to the seal to hold it in place.

 

Yamaha did make a spacer to retain the left seal on the 68 DT1 ,
later redesigning the stator plate , to do the same job .
The spacer is detailed in Parts bulletin  #241 . Unfortunately I don't have a copy ,
as my bulletins start at # 242 ( Murphy's Law ) .
There may be a copy in the Tech Section .

Yep I acquired the seal retainer for my 68 DT1 build. I thought it was strange but from 68DT1’s description I will install it. Yes goes between stator plate and seal. Thanks again for the heads up!

Here’s Service Bulletin #241

** It appears that site I has reached its maximum capacity and can no longer accept images. I sent as PM for now. 

I can’t seem to attach image to a Message also… so here’s the part # and they seem to be readily available.

NOS Yamaha 1968 DT1 Crankcase Retainer Seal PART# 214-15317-09