Great post Enduronut. Fingers crossed it all hangs together for msavitt.
By memory they're quite a long piston with no holes of course being piston port & probably small ports.
So hopefully things in its favour--or favor depending where you live. Computer underlines so much of my spelling lol.

Hi enduronut - 

I am glad you commented, you actually did me a favor by answering the question I posed.  I asked the question because it seemed too easy.  I decided to go for it because  nobody said “stupid idea”!  

If after all this work I blow up the motor then I would be stupid to not take an alternative approach.  I spent next to nothing on the 2nd oversize piston set so I am going to pivot.

I am going to PM you to follow up on this. 

thanks for your commentary , it’s sincerely appreciated!

based on Enduronut's advice I put the brakes on my backwards piston idea, new pistons and rings ID'ed with his help, we will see what arrives in the mail!  Bit progress on rebuilding the chassis after stripping down and now putting back together.  Big lucky break - all the cables were in good shape so I was able to get all of them in nice working order with an overdose of BBQ lighter fluid, WD40 and light machine oil.  Once I get the pistons I can get the bores done.  Once I get the crank back with new un-bent rod back I can hopefully get this cute little motor back together and this little beauty out on the road.  I told my wife that its "too small for me so I will sell it on" as a way to get #6, but I got a feeling that I may fall in love with this one.

share.icloud.com/photos/0f42ZgIj8axv9s1O_Vk5HtqFA

Wise decision my best friend dad bought him a new one  I remember him putting a knobby tire on it to ride the trails with us. I really like the cigar tank as we called it. You have a marantz receiver cool and a Vw. 

And Bose 301 speakers!

my LS2 had a knobby on the rear, maybe it was yours!  Mine had only 2000 miles on odo but had the crap beat out of it. 

Interesting I remember him getting stuck in a mud water rut and the exhaust was underwater and blowing bubbles but he did keep it clean and serviced

My blue one i made a two into one high pipe going into an original DT2MX tail muffler & my brother rode it in a slippery hair scramble with muddy patches. Had mx tires on but it was terrible haha. Made no power i realized later because of not using the original pipes & mufflers which were tuned to make the most of the little cylinders. Motor sounded sweet like that--& ran nice--albeit gutless.

My DS7 runs sweeter than my R5C.  Maybe my little 100 will be even smoother 

Hello Msavitt,
 There is one of these little bikes in the shed here that needs similar attention. It appeared to have been sheltered most of its life but then previous owner removed carbs and stored it outside so engine filled with rain and seized up. 
  Perhaps there is something about this model that makes owners abuse them .
  My plan has been to accumulate parts needed as they show up and one day restore it .  As you mentioned they might be a smooth running engine with the iron cylinders and tiny pistons. 
  The cable guide on front fender seemed very similar to the enduro ones. Suppose Yamaha could have used one already available. 
 Interesting story you’ve got going on here as it is more challenging restoring the more rare models. First start up will be rewarding !! I’ve got the 100 cc single cylinder street bike and that one does run and it’s a hoot to drive.