Pretty sure I have a bad crank seal...

[speedfrk]

Got the bike all back together and it runs very well. All stock 84 with 4K miles. Rode it gently over to my friends house and noticed a lot of smoke but it did have pre-mix and the oil injection working at the same time but on the way home, crazy amount of smoke that then suddenly ceased smoking and the rt side pipe was hot enough to burn off the new paint where the converter is. Checked the gearbox oil and it is super low so it must have been burning it. Bike still ran fine but I hope I didn't screw up that piston... Time to take it all apart again I guess.

[Yamavarna]

I would perform a leak down or pressure test. The kits aren’t that expensive

[JonW]

OEM seal?

[MK]

That's pretty clearly the right hand crank seal.
Usually damaged by a failed bearing.

Diagnosis is easy. Get off the RH cover and the primary gear on the crank. Pull you the gear and closely inspect the area between crank seal and bearing.
Usually there's some debris from the bearing cage and the seal lip spring.

[Darrell]

And just as an aside, it's a bad idea to run premix AND oil injection.

[speedfrk]

Sorry, I wasn't clear- the engine has never been apart, the bike was for cleaning. It's a 4K mile bike and I was "hoping" it would be OK because it is so pristine. But I pretty much expected what happened. I rolled the dice and lost, lol.

[tacky1]

Id say the seal is gone especially if it hasn't been apart, The seals fail with age, They are 40 year old seals in there, plus the newer fuels seem to eat them...

[JonW]

yep, old seals = dead seals.

Time for a refurb.

[JanBros]

And just as an aside, it's a bad idea to run premix AND oil injection.

why ?
no engine has ever been hurt from more oil. as opposed to less oil.

[Darrell]

You're actually leaning out your air-fuel mixture when you put in too much oil. That probably won't matter much if you're running rich anyway, but if you're right on the edge of running lean it could. Your plugs will foul more quickly, too, with twice as much oil as the bike needs. Stick your finger in the outlet of the exhaust stinger of a bike running the recommended amount of oil and you'll come away with a black, oily finger. That oil eventually clogs the silencer which restricts your exhaust. You might imagine that if you're running twice the recommended oil that the amount of oil that passes unburned goes up. Your YPVS valves get gummy and need to be cleaned even when you run high-quality synthetic two-stroke oil. Putting twice as much through the system will gum them up faster. And some of that unburned oil is going to end up as carbon deposits on the top of your pistons. Those deposits can get hot and cause detonation in some cases.

Back when I started racing two strokes... WAY back.... we used Castor bean oil and it left a lot of deposits behind. (But I still love the smell of burning Castor oil!) Modern synthetics are way, way better, which allows us to use less. More isn't always better.

[JanBros]

You're actually leaning out your air-fuel mixture when you put in too much oil. That probably won't matter much if you're running rich anyway, but if you're right on the edge of running lean it could. Your plugs will foul more quickly, too, with twice as much oil as the bike needs. Stick your finger in the outlet of the exhaust stinger of a bike running the recommended amount of oil and you'll come away with a black, oily finger. That oil eventually clogs the silencer which restricts your exhaust. You might imagine that if you're running twice the recommended oil that the amount of oil that passes unburned goes up. Your YPVS valves get gummy and need to be cleaned even when you run high-quality synthetic two-stroke oil. Putting twice as much through the system will gum them up faster. And some of that unburned oil is going to end up as carbon deposits on the top of your pistons. Those deposits can get hot and cause detonation in some cases.

Back when I started racing two strokes... WAY back.... we used Castor bean oil and it left a lot of deposits behind. (But I still love the smell of burning Castor oil!) Modern synthetics are way, way better, which allows us to use less. More isn't always better.

agree with all this, but that means more oil is bad ONLY if you do not adjust your mixture, AND it depends on your riding style. On my KR1S my oilpump is richer than original AND I use top quality oil. never had a seizure since I'm running like this in 15 years. Before (original settings oilpump and just good oil) I've had a couple of engine failures. But I use my bike the way Kawa developped it : it barely runs outside the powerband going "slow" (with/without more oil) means your engine never get's hot enough to burn the oil.
I do Moped-MX-endurance (up to 10 or even 24hour races) and have a KDX250 use 4% top quality oil. never had an engine failure. People ask me why so much oil when 2% is ok with top oils today and my only answer is : have you ever seen one of my engines fail ? also tests have shown more oil is better for performance. burning the oil gives hardly less power than burning fuel, but the extra oil gives better sealing between piston and cylinder and gives more power.

Cruising arround on a 2-stroke will always lead to too much unburnt oill (unless you lower the amount of oil, but than you risk your engine if you do open the throttle)
and yes you might have to clean your engine more often with more oil, but cleaning is still much much cheaper than repairing a broken engine. with or without more oil.

so as always, just saying "it's bad" is very oversimplifying things and certainly not as bad as you made it sound with your original simple message, and it CAN BE better for the engine.

[speedfrk]

I was only running both during first start and until I had the lines bled out. Anyways, it's apart and you can see how much gearbox oil is on the crank. The seal seems to be very soft and pliable with no obvious damage but you can see a brown residue on the inside lip of the seal which almost looks like rust except it was a very oily engine. But it definitely got hot looking at the exhaust. Pistons look fine.

[MK]

That brown "rust" is the Teflon sealing lip that sometimes comes loose, especially in very old engines.

Astonishingly I see no obvious damage, so the oil may has come a different path?
The second possibility is the oil pump seal. I'd replace that in any case as you already opened the engine.
(But this would have yielded in an empty two-stroke oil tank and overfilled gearbox oil)

[speedfrk]

Thanks, Martin... Yeah, the seal looks perfect and the oil tank was still full. I did replace the gasket where the oil pump mounts to the clutch cover but not the shaft seal. It was also in remarkably good condition and very soft and supple like the crank seal. The oil that was covering the crank and in the bottom of the case is clear like motor oil and not bluish like the injection oil. Plus, the gearbox oil was definitely lower than when I filled it. So, not sure exactly what is going on but maybe the spring around the seal lip is just very weak and allowing oil/air to be sucked in. And, the rt exhaust got very hot- enough to burn off the paint.

[MK]

I'm still not convinced that it was the right hand crank seal.
I've seen lots of damages here and ALL of them were pretty obvious like disintegrated bearing or the "rust" lip fallen off.
There is no such thing as a weak spring.

In my last case I could even diagnose it very well without opening the engine.
Bike ran well without suspicious noise, but mirror showed excessive smoke. Rode calmly to avoid further damage - smoke got "normal", but gearbox oil level was low.
Leaning bike to the right brought back the smoke immediately.
Opening the engine showed damage bearing cage that damaged the seal.

In your case, as the engine is already out, I'd open the case fully.
When assembling with a set of new Yamaha OEM seals, apply the correct sealing compound to the mating surfaces.
That eliminates all possible sources for gearbox oil entering the crankcase.