1968 Yamaha YCS1C

Got the switch sorted out thanks to help from the guys over at 2strokeworld. It was like unraveling a sweater though -- the wiring for starter, signals and lights had all been clipped off and electical taped into the harness in random places. I would pull at one spot to try and find a wire and end up unwrapping 3 feet of gooey, oily electrical tape to find the correct wire that had been cut off years ago.

It looks like a huge rats nest right now and I have wires going every which way -- but -- they all are now color correct and have bulleted connectors on them. And more good news: the engine turns over with the starter and I have spark to both plugs!

Also took a few minutes to draw a color wiring diagram:

colorycswiring1-2.png


My gauge is not the YCS one so I am working on figuring out the wiring for that. It has far less wires than the stock gauge does. I also appear to be completely missing the wiring to the neutral safety switch. Since it's plausible that my girlfriend may end up riding this bike, I'm going to try route this and hook up the gauges and idiot lights correctly. Slow but steady progress today!
 
Hey guys -- I'm back and working on this bike again!!

At some point last summer I started to try and get it to run and was worried that the RH cylinder seemed to have low compression. I got super frustrated with the carbs and intake boot and instead of burning down the garage, I decided to just move on to other projects.

I started thinking/planning out what I wanted and it kept coming back to stripping this down and making it simpler. Here's what I've decided to do:

- Remove the trouble-some airbox and snorkel. Run the uni foam pod-filters. My research looks like as long as they are all foam, I should be OK but it's a bit uncharted if I need to go up a jet size or not. I'll stick with stock for now and see what it looks like.
- Bypass the oil pump. The oil pump works fine but I don't have a good looking tank or side cover for the other side. Since I'm going to run pod filters, I need to try and open up the middle of the bike for that groovy "cafe" look. Battery will be relocated under the seat w/ a voltage regulator and whatever other electronics I'll need.

First step? Check compression. I finally bought a compression tester and I'm confused with what I'm finding. The LH cylinder is reading 90psi -- the RH one is 0. Doesn't even move the needle. Is this even possible?

Regardless -- I'm going to start tearing into it and see what I find. I found new head and base gaskets on eBay and pistons are readily available. Should be easy to have this bored out .025 if needed. I'll try and take photos and report back what I find.
 
Glad to see you back sir.

I worry about 0 because that might mean the piston wasn't moving at all....although I truly have never seen a "0" so someone else might be able to chime in!?

Either way, you gotta pull her apart, take some pics and let us know how she goes.
 
Hey Bruno! Glad to see you're still here. Love your mono-shock build!!

Pulled the motor and took the heads off and found the problem pretty quickly. RH cylinder only had 1 ring, and that ring was split in half!

20130530_191637_zpsf7a16575.jpg


So where did the other ring go? Looks like it was punched into dust by the top of the piston.

20130530_191718_zpse5c125ed.jpg


Here's the weird thing.... the RH cylinder itself looks good. No idea how the piston can be damaged, the ring can be destroyed and the cylinder itself can still be OK?

20130530_191934_zpse4564964.jpg


As you can see -- the LH cylinder isn't nearly as clean!

20130530_191947_zpsc6dd71fc.jpg


20130530_191914_zps21983a40.jpg


Here's my question. Do I get this bored over and get over-sized pistons? Or do I hone it and put standard pistons back in?

The other question -- Do I need to replace this head? Looks like the ring was beat into the bottom of the spark plug over and over and over again until it quit. Since this is a piston port engine, does this even make a difference?

20130530_192138_zps3851ec35.jpg


Here's the LH head for reference -- just carbon, no damage.

20130530_192149_zps544dae58.jpg


20130530_192155_zpsf8a534ed.jpg
 
Yup. Still here! The mono-shock is coming right along now...haha.

I'll leave the engine questions to Teazer and the gang, they know far more about that than I would. I'm still a relative new guy to 2 stroke engine work. This will be a cool ride though when done.
 
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