Just spent a week getting my old '71 CT-1 running, and on the second trip around the block it started smoking and running badly. I concluded that I probably have bad crankshaft seals, so I just took it apart. I found quite a bit of 2-stroke oil in the clutch/gearbox area. The seal is intact, but I guess this confirms that the seal is leaking, correct? If it can leak one way, it can leak the other way. I haven't pulled the Magneto yet, but it looks pretty clean in there. I already ordered a set of seals from Rusty Riders, I hope those will work as well as factory, or should I order factory? It doesn't show up much in the pictures, but that you can see the color of the 2-stroke oil in it in person very well. 

your primary side crankshaft seal is leaking and it was drawing in transmission oil and causing it to smoke more heavily and run bad. I would replace both crankshaft seals. might want to check the crankshaft main bearings and make sure there is no play or roughness when the engine is kicked through. it will make a rumble type of noise if the bearings are bad.

when the engine sits, two stroke oil is getting past the seal and entering the transmission.

if you can get them, I would get factory seals.

I had been advised on the forum to use genuine Yamaha crank seals and upgrade the magneto seal to the one from an IT175

Be careful you don't lose that shim that is against the white plastic gear. It is just sitting there and mine fell off as I was handling the engine. Took awhile for me to figure out where it went.....

I ordered all of my seals from my local Yamaha shop. Also ordered front and rear brakes. The total came to $153.70 and I ordered them on Feb 19th. I'm still waiting....

 

Yes, Yamaha seals from 77-79 IT175 are best...  dual lip on both.  (Clutch side seal is the same part on CT and IT)

I'd consider changing the oil pump shaft seal in the clutch cover.  That's probably the most likely source for visible two stroke oil in transmission?

Yep I found those white shims and have them safely stored. Also the little spring and ball bearing that came out of the injector pump outlet, and I realize where that goes. When I took off the autolube pump, I think that was where a lot of the leak was coming from, the shaft for the worm gear.

I got all the screws for the clutch taken off with a impact driver, and I used a large strap wrench to hold the clutch, and also to hold the primary gear when I took its nut off with an impact wrench. But I had a problem on the stator plate. I have a very old craftsman impact driver, and the bits for a didn't really fit that well into the screws. I finally just drilled off the head of one of the screws. Underneath the stator plate I found one screw loose. It's on the left of this picture. I think that's what was causing a rattling noise I could hear it idle. I snugged itback up, and a couple of the others were slightly loose.

I think seal kit I ordered has all of the seals in it, I may end up using that, we'll see. But I'll check around to see if I can dig up some Yamaha seals. There's also a few other parts and washers that fell out, but I figured out where they all go.

 

Well this made my week!. I drilled a tiny hole in the center of the remaining part of the stator screw,, then stuck a flat head prrecision screwdriver in it, and it easily twisted right out! No damage to the threads at all. Just have to find a couple new screws.

By the way, when that flywheel pops off, it's a pretty violent POP! So at this point I'm just going to wait until the seals I ordered arrive in a couple days, and see what they look like, and if they don't look kosher I'll look around for the Yamaha seals.

 

How did you determin twostroke oil is getting into the trans oil. was it an obvious color change separating them out. Or did the level rise a lot on the dipstick. Or--more likely i misunderstood what you described. Broken screws are a pain. Good you saved the day. Crank seals dont usualy leak but 'do' get blown out of the case although yours isn't. Is it likely the muffler was just getting hot & smouldering internaly & had fouled a plug or a lump of loose carboin had blocked the spark arrestor. Ok i'm a bugger for going for unlikely options so look forward to hearing it runs well after a crank seal & oil pump seal.

Initially it was running great, and the smoke looked normal, but then on my second trip around the block to smoke turned into sort of a whitish grey and smelled like transmission oil. I have seen numerous threads on many forums talking about those old crankshaft seals, that's why I decided to take it apart.

Actually I had noticed that the transmission oil was going down, but when I opened it up, that's when I noticed the blue-green color of the 2-stroke oil inside the gearbox. As someone else said, it was probably sleeping in there after I shut it down. One thing I'm glad about, is I found that loose case screw behind the stator.

I just got back from Ace Hardware, and found screws that are an exact replacement. They are M6 x 1.0 thread.

I don't know, it's possible the exhaust is plugged up or something I'm not really sure how to check that.

 

You say a case screw behind the stator but show a stator screw. So i guess you mean't stator plate screw. Only i was just thinking--if ya meant case screw --as in crankcase--behing the stator, that could [slightly possibly] be your smoking issue getting sucked in from the trans through the center case joint. I'll guess i'm mis interpreting things at this stage though. Hope for good new in the end.